[PATCH 1/2] Documentation: move all DMA documentations into Documentaion/dma
From: hongbo.zhang
Date: Thu Jan 16 2014 - 05:39:17 EST
From: Hongbo Zhang <hongbo.zhang@xxxxxxxxxxxxx>
Since there are already seven DMA documentations under the top Documentation/,
it is better to create one dedicated directory for them.
Signed-off-by: Hongbo Zhang <hongbo.zhang@xxxxxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxx>
Cc: Richard Henderson <rth@xxxxxxxxxx>
Cc: Jakub Jelinek <jakub@xxxxxxxxxx>
Cc: James E.J. Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Arthur Kepner <akepner@xxxxxxx>
Cc: sumit.semwal@xxxxxxxxxx
Cc: Vinod Koul <vinod.koul@xxxxxxxxx>
Cc: Pierre Ossman <drzeus@xxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
---
Documentation/DMA-API-HOWTO.txt | 915 ---------------------------------
Documentation/DMA-API.txt | 700 -------------------------
Documentation/DMA-ISA-LPC.txt | 151 ------
Documentation/DMA-attributes.txt | 102 ----
Documentation/dma-buf-sharing.txt | 462 -----------------
Documentation/dma/DMA-API-HOWTO.txt | 915 +++++++++++++++++++++++++++++++++
Documentation/dma/DMA-API.txt | 700 +++++++++++++++++++++++++
Documentation/dma/DMA-ISA-LPC.txt | 151 ++++++
Documentation/dma/DMA-attributes.txt | 102 ++++
Documentation/dma/dma-buf-sharing.txt | 462 +++++++++++++++++
Documentation/dma/dmaengine.txt | 198 +++++++
Documentation/dma/dmatest.txt | 92 ++++
Documentation/dmaengine.txt | 198 -------
Documentation/dmatest.txt | 92 ----
14 files changed, 2620 insertions(+), 2620 deletions(-)
delete mode 100644 Documentation/DMA-API-HOWTO.txt
delete mode 100644 Documentation/DMA-API.txt
delete mode 100644 Documentation/DMA-ISA-LPC.txt
delete mode 100644 Documentation/DMA-attributes.txt
delete mode 100644 Documentation/dma-buf-sharing.txt
create mode 100644 Documentation/dma/DMA-API-HOWTO.txt
create mode 100644 Documentation/dma/DMA-API.txt
create mode 100644 Documentation/dma/DMA-ISA-LPC.txt
create mode 100644 Documentation/dma/DMA-attributes.txt
create mode 100644 Documentation/dma/dma-buf-sharing.txt
create mode 100644 Documentation/dma/dmaengine.txt
create mode 100644 Documentation/dma/dmatest.txt
delete mode 100644 Documentation/dmaengine.txt
delete mode 100644 Documentation/dmatest.txt
diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt
deleted file mode 100644
index 5e98303..0000000
--- a/Documentation/DMA-API-HOWTO.txt
+++ /dev/null
@@ -1,915 +0,0 @@
- Dynamic DMA mapping Guide
- =========================
-
- David S. Miller <davem@xxxxxxxxxx>
- Richard Henderson <rth@xxxxxxxxxx>
- Jakub Jelinek <jakub@xxxxxxxxxx>
-
-This is a guide to device driver writers on how to use the DMA API
-with example pseudo-code. For a concise description of the API, see
-DMA-API.txt.
-
-Most of the 64bit platforms have special hardware that translates bus
-addresses (DMA addresses) into physical addresses. This is similar to
-how page tables and/or a TLB translates virtual addresses to physical
-addresses on a CPU. This is needed so that e.g. PCI devices can
-access with a Single Address Cycle (32bit DMA address) any page in the
-64bit physical address space. Previously in Linux those 64bit
-platforms had to set artificial limits on the maximum RAM size in the
-system, so that the virt_to_bus() static scheme works (the DMA address
-translation tables were simply filled on bootup to map each bus
-address to the physical page __pa(bus_to_virt())).
-
-So that Linux can use the dynamic DMA mapping, it needs some help from the
-drivers, namely it has to take into account that DMA addresses should be
-mapped only for the time they are actually used and unmapped after the DMA
-transfer.
-
-The following API will work of course even on platforms where no such
-hardware exists.
-
-Note that the DMA API works with any bus independent of the underlying
-microprocessor architecture. You should use the DMA API rather than
-the bus specific DMA API (e.g. pci_dma_*).
-
-First of all, you should make sure
-
-#include <linux/dma-mapping.h>
-
-is in your driver. This file will obtain for you the definition of the
-dma_addr_t (which can hold any valid DMA address for the platform)
-type which should be used everywhere you hold a DMA (bus) address
-returned from the DMA mapping functions.
-
- What memory is DMA'able?
-
-The first piece of information you must know is what kernel memory can
-be used with the DMA mapping facilities. There has been an unwritten
-set of rules regarding this, and this text is an attempt to finally
-write them down.
-
-If you acquired your memory via the page allocator
-(i.e. __get_free_page*()) or the generic memory allocators
-(i.e. kmalloc() or kmem_cache_alloc()) then you may DMA to/from
-that memory using the addresses returned from those routines.
-
-This means specifically that you may _not_ use the memory/addresses
-returned from vmalloc() for DMA. It is possible to DMA to the
-_underlying_ memory mapped into a vmalloc() area, but this requires
-walking page tables to get the physical addresses, and then
-translating each of those pages back to a kernel address using
-something like __va(). [ EDIT: Update this when we integrate
-Gerd Knorr's generic code which does this. ]
-
-This rule also means that you may use neither kernel image addresses
-(items in data/text/bss segments), nor module image addresses, nor
-stack addresses for DMA. These could all be mapped somewhere entirely
-different than the rest of physical memory. Even if those classes of
-memory could physically work with DMA, you'd need to ensure the I/O
-buffers were cacheline-aligned. Without that, you'd see cacheline
-sharing problems (data corruption) on CPUs with DMA-incoherent caches.
-(The CPU could write to one word, DMA would write to a different one
-in the same cache line, and one of them could be overwritten.)
-
-Also, this means that you cannot take the return of a kmap()
-call and DMA to/from that. This is similar to vmalloc().
-
-What about block I/O and networking buffers? The block I/O and
-networking subsystems make sure that the buffers they use are valid
-for you to DMA from/to.
-
- DMA addressing limitations
-
-Does your device have any DMA addressing limitations? For example, is
-your device only capable of driving the low order 24-bits of address?
-If so, you need to inform the kernel of this fact.
-
-By default, the kernel assumes that your device can address the full
-32-bits. For a 64-bit capable device, this needs to be increased.
-And for a device with limitations, as discussed in the previous
-paragraph, it needs to be decreased.
-
-Special note about PCI: PCI-X specification requires PCI-X devices to
-support 64-bit addressing (DAC) for all transactions. And at least
-one platform (SGI SN2) requires 64-bit consistent allocations to
-operate correctly when the IO bus is in PCI-X mode.
-
-For correct operation, you must interrogate the kernel in your device
-probe routine to see if the DMA controller on the machine can properly
-support the DMA addressing limitation your device has. It is good
-style to do this even if your device holds the default setting,
-because this shows that you did think about these issues wrt. your
-device.
-
-The query is performed via a call to dma_set_mask_and_coherent():
-
- int dma_set_mask_and_coherent(struct device *dev, u64 mask);
-
-which will query the mask for both streaming and coherent APIs together.
-If you have some special requirements, then the following two separate
-queries can be used instead:
-
- The query for streaming mappings is performed via a call to
- dma_set_mask():
-
- int dma_set_mask(struct device *dev, u64 mask);
-
- The query for consistent allocations is performed via a call
- to dma_set_coherent_mask():
-
- int dma_set_coherent_mask(struct device *dev, u64 mask);
-
-Here, dev is a pointer to the device struct of your device, and mask
-is a bit mask describing which bits of an address your device
-supports. It returns zero if your card can perform DMA properly on
-the machine given the address mask you provided. In general, the
-device struct of your device is embedded in the bus specific device
-struct of your device. For example, a pointer to the device struct of
-your PCI device is pdev->dev (pdev is a pointer to the PCI device
-struct of your device).
-
-If it returns non-zero, your device cannot perform DMA properly on
-this platform, and attempting to do so will result in undefined
-behavior. You must either use a different mask, or not use DMA.
-
-This means that in the failure case, you have three options:
-
-1) Use another DMA mask, if possible (see below).
-2) Use some non-DMA mode for data transfer, if possible.
-3) Ignore this device and do not initialize it.
-
-It is recommended that your driver print a kernel KERN_WARNING message
-when you end up performing either #2 or #3. In this manner, if a user
-of your driver reports that performance is bad or that the device is not
-even detected, you can ask them for the kernel messages to find out
-exactly why.
-
-The standard 32-bit addressing device would do something like this:
-
- if (dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32))) {
- printk(KERN_WARNING
- "mydev: No suitable DMA available.\n");
- goto ignore_this_device;
- }
-
-Another common scenario is a 64-bit capable device. The approach here
-is to try for 64-bit addressing, but back down to a 32-bit mask that
-should not fail. The kernel may fail the 64-bit mask not because the
-platform is not capable of 64-bit addressing. Rather, it may fail in
-this case simply because 32-bit addressing is done more efficiently
-than 64-bit addressing. For example, Sparc64 PCI SAC addressing is
-more efficient than DAC addressing.
-
-Here is how you would handle a 64-bit capable device which can drive
-all 64-bits when accessing streaming DMA:
-
- int using_dac;
-
- if (!dma_set_mask(dev, DMA_BIT_MASK(64))) {
- using_dac = 1;
- } else if (!dma_set_mask(dev, DMA_BIT_MASK(32))) {
- using_dac = 0;
- } else {
- printk(KERN_WARNING
- "mydev: No suitable DMA available.\n");
- goto ignore_this_device;
- }
-
-If a card is capable of using 64-bit consistent allocations as well,
-the case would look like this:
-
- int using_dac, consistent_using_dac;
-
- if (!dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64))) {
- using_dac = 1;
- consistent_using_dac = 1;
- } else if (!dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32))) {
- using_dac = 0;
- consistent_using_dac = 0;
- } else {
- printk(KERN_WARNING
- "mydev: No suitable DMA available.\n");
- goto ignore_this_device;
- }
-
-The coherent coherent mask will always be able to set the same or a
-smaller mask as the streaming mask. However for the rare case that a
-device driver only uses consistent allocations, one would have to
-check the return value from dma_set_coherent_mask().
-
-Finally, if your device can only drive the low 24-bits of
-address you might do something like:
-
- if (dma_set_mask(dev, DMA_BIT_MASK(24))) {
- printk(KERN_WARNING
- "mydev: 24-bit DMA addressing not available.\n");
- goto ignore_this_device;
- }
-
-When dma_set_mask() or dma_set_mask_and_coherent() is successful, and
-returns zero, the kernel saves away this mask you have provided. The
-kernel will use this information later when you make DMA mappings.
-
-There is a case which we are aware of at this time, which is worth
-mentioning in this documentation. If your device supports multiple
-functions (for example a sound card provides playback and record
-functions) and the various different functions have _different_
-DMA addressing limitations, you may wish to probe each mask and
-only provide the functionality which the machine can handle. It
-is important that the last call to dma_set_mask() be for the
-most specific mask.
-
-Here is pseudo-code showing how this might be done:
-
- #define PLAYBACK_ADDRESS_BITS DMA_BIT_MASK(32)
- #define RECORD_ADDRESS_BITS DMA_BIT_MASK(24)
-
- struct my_sound_card *card;
- struct device *dev;
-
- ...
- if (!dma_set_mask(dev, PLAYBACK_ADDRESS_BITS)) {
- card->playback_enabled = 1;
- } else {
- card->playback_enabled = 0;
- printk(KERN_WARNING "%s: Playback disabled due to DMA limitations.\n",
- card->name);
- }
- if (!dma_set_mask(dev, RECORD_ADDRESS_BITS)) {
- card->record_enabled = 1;
- } else {
- card->record_enabled = 0;
- printk(KERN_WARNING "%s: Record disabled due to DMA limitations.\n",
- card->name);
- }
-
-A sound card was used as an example here because this genre of PCI
-devices seems to be littered with ISA chips given a PCI front end,
-and thus retaining the 16MB DMA addressing limitations of ISA.
-
- Types of DMA mappings
-
-There are two types of DMA mappings:
-
-- Consistent DMA mappings which are usually mapped at driver
- initialization, unmapped at the end and for which the hardware should
- guarantee that the device and the CPU can access the data
- in parallel and will see updates made by each other without any
- explicit software flushing.
-
- Think of "consistent" as "synchronous" or "coherent".
-
- The current default is to return consistent memory in the low 32
- bits of the bus space. However, for future compatibility you should
- set the consistent mask even if this default is fine for your
- driver.
-
- Good examples of what to use consistent mappings for are:
-
- - Network card DMA ring descriptors.
- - SCSI adapter mailbox command data structures.
- - Device firmware microcode executed out of
- main memory.
-
- The invariant these examples all require is that any CPU store
- to memory is immediately visible to the device, and vice
- versa. Consistent mappings guarantee this.
-
- IMPORTANT: Consistent DMA memory does not preclude the usage of
- proper memory barriers. The CPU may reorder stores to
- consistent memory just as it may normal memory. Example:
- if it is important for the device to see the first word
- of a descriptor updated before the second, you must do
- something like:
-
- desc->word0 = address;
- wmb();
- desc->word1 = DESC_VALID;
-
- in order to get correct behavior on all platforms.
-
- Also, on some platforms your driver may need to flush CPU write
- buffers in much the same way as it needs to flush write buffers
- found in PCI bridges (such as by reading a register's value
- after writing it).
-
-- Streaming DMA mappings which are usually mapped for one DMA
- transfer, unmapped right after it (unless you use dma_sync_* below)
- and for which hardware can optimize for sequential accesses.
-
- This of "streaming" as "asynchronous" or "outside the coherency
- domain".
-
- Good examples of what to use streaming mappings for are:
-
- - Networking buffers transmitted/received by a device.
- - Filesystem buffers written/read by a SCSI device.
-
- The interfaces for using this type of mapping were designed in
- such a way that an implementation can make whatever performance
- optimizations the hardware allows. To this end, when using
- such mappings you must be explicit about what you want to happen.
-
-Neither type of DMA mapping has alignment restrictions that come from
-the underlying bus, although some devices may have such restrictions.
-Also, systems with caches that aren't DMA-coherent will work better
-when the underlying buffers don't share cache lines with other data.
-
-
- Using Consistent DMA mappings.
-
-To allocate and map large (PAGE_SIZE or so) consistent DMA regions,
-you should do:
-
- dma_addr_t dma_handle;
-
- cpu_addr = dma_alloc_coherent(dev, size, &dma_handle, gfp);
-
-where device is a struct device *. This may be called in interrupt
-context with the GFP_ATOMIC flag.
-
-Size is the length of the region you want to allocate, in bytes.
-
-This routine will allocate RAM for that region, so it acts similarly to
-__get_free_pages (but takes size instead of a page order). If your
-driver needs regions sized smaller than a page, you may prefer using
-the dma_pool interface, described below.
-
-The consistent DMA mapping interfaces, for non-NULL dev, will by
-default return a DMA address which is 32-bit addressable. Even if the
-device indicates (via DMA mask) that it may address the upper 32-bits,
-consistent allocation will only return > 32-bit addresses for DMA if
-the consistent DMA mask has been explicitly changed via
-dma_set_coherent_mask(). This is true of the dma_pool interface as
-well.
-
-dma_alloc_coherent returns two values: the virtual address which you
-can use to access it from the CPU and dma_handle which you pass to the
-card.
-
-The cpu return address and the DMA bus master address are both
-guaranteed to be aligned to the smallest PAGE_SIZE order which
-is greater than or equal to the requested size. This invariant
-exists (for example) to guarantee that if you allocate a chunk
-which is smaller than or equal to 64 kilobytes, the extent of the
-buffer you receive will not cross a 64K boundary.
-
-To unmap and free such a DMA region, you call:
-
- dma_free_coherent(dev, size, cpu_addr, dma_handle);
-
-where dev, size are the same as in the above call and cpu_addr and
-dma_handle are the values dma_alloc_coherent returned to you.
-This function may not be called in interrupt context.
-
-If your driver needs lots of smaller memory regions, you can write
-custom code to subdivide pages returned by dma_alloc_coherent,
-or you can use the dma_pool API to do that. A dma_pool is like
-a kmem_cache, but it uses dma_alloc_coherent not __get_free_pages.
-Also, it understands common hardware constraints for alignment,
-like queue heads needing to be aligned on N byte boundaries.
-
-Create a dma_pool like this:
-
- struct dma_pool *pool;
-
- pool = dma_pool_create(name, dev, size, align, alloc);
-
-The "name" is for diagnostics (like a kmem_cache name); dev and size
-are as above. The device's hardware alignment requirement for this
-type of data is "align" (which is expressed in bytes, and must be a
-power of two). If your device has no boundary crossing restrictions,
-pass 0 for alloc; passing 4096 says memory allocated from this pool
-must not cross 4KByte boundaries (but at that time it may be better to
-go for dma_alloc_coherent directly instead).
-
-Allocate memory from a dma pool like this:
-
- cpu_addr = dma_pool_alloc(pool, flags, &dma_handle);
-
-flags are SLAB_KERNEL if blocking is permitted (not in_interrupt nor
-holding SMP locks), SLAB_ATOMIC otherwise. Like dma_alloc_coherent,
-this returns two values, cpu_addr and dma_handle.
-
-Free memory that was allocated from a dma_pool like this:
-
- dma_pool_free(pool, cpu_addr, dma_handle);
-
-where pool is what you passed to dma_pool_alloc, and cpu_addr and
-dma_handle are the values dma_pool_alloc returned. This function
-may be called in interrupt context.
-
-Destroy a dma_pool by calling:
-
- dma_pool_destroy(pool);
-
-Make sure you've called dma_pool_free for all memory allocated
-from a pool before you destroy the pool. This function may not
-be called in interrupt context.
-
- DMA Direction
-
-The interfaces described in subsequent portions of this document
-take a DMA direction argument, which is an integer and takes on
-one of the following values:
-
- DMA_BIDIRECTIONAL
- DMA_TO_DEVICE
- DMA_FROM_DEVICE
- DMA_NONE
-
-One should provide the exact DMA direction if you know it.
-
-DMA_TO_DEVICE means "from main memory to the device"
-DMA_FROM_DEVICE means "from the device to main memory"
-It is the direction in which the data moves during the DMA
-transfer.
-
-You are _strongly_ encouraged to specify this as precisely
-as you possibly can.
-
-If you absolutely cannot know the direction of the DMA transfer,
-specify DMA_BIDIRECTIONAL. It means that the DMA can go in
-either direction. The platform guarantees that you may legally
-specify this, and that it will work, but this may be at the
-cost of performance for example.
-
-The value DMA_NONE is to be used for debugging. One can
-hold this in a data structure before you come to know the
-precise direction, and this will help catch cases where your
-direction tracking logic has failed to set things up properly.
-
-Another advantage of specifying this value precisely (outside of
-potential platform-specific optimizations of such) is for debugging.
-Some platforms actually have a write permission boolean which DMA
-mappings can be marked with, much like page protections in the user
-program address space. Such platforms can and do report errors in the
-kernel logs when the DMA controller hardware detects violation of the
-permission setting.
-
-Only streaming mappings specify a direction, consistent mappings
-implicitly have a direction attribute setting of
-DMA_BIDIRECTIONAL.
-
-The SCSI subsystem tells you the direction to use in the
-'sc_data_direction' member of the SCSI command your driver is
-working on.
-
-For Networking drivers, it's a rather simple affair. For transmit
-packets, map/unmap them with the DMA_TO_DEVICE direction
-specifier. For receive packets, just the opposite, map/unmap them
-with the DMA_FROM_DEVICE direction specifier.
-
- Using Streaming DMA mappings
-
-The streaming DMA mapping routines can be called from interrupt
-context. There are two versions of each map/unmap, one which will
-map/unmap a single memory region, and one which will map/unmap a
-scatterlist.
-
-To map a single region, you do:
-
- struct device *dev = &my_dev->dev;
- dma_addr_t dma_handle;
- void *addr = buffer->ptr;
- size_t size = buffer->len;
-
- dma_handle = dma_map_single(dev, addr, size, direction);
- if (dma_mapping_error(dma_handle)) {
- /*
- * reduce current DMA mapping usage,
- * delay and try again later or
- * reset driver.
- */
- goto map_error_handling;
- }
-
-and to unmap it:
-
- dma_unmap_single(dev, dma_handle, size, direction);
-
-You should call dma_mapping_error() as dma_map_single() could fail and return
-error. Not all dma implementations support dma_mapping_error() interface.
-However, it is a good practice to call dma_mapping_error() interface, which
-will invoke the generic mapping error check interface. Doing so will ensure
-that the mapping code will work correctly on all dma implementations without
-any dependency on the specifics of the underlying implementation. Using the
-returned address without checking for errors could result in failures ranging
-from panics to silent data corruption. A couple of examples of incorrect ways
-to check for errors that make assumptions about the underlying dma
-implementation are as follows and these are applicable to dma_map_page() as
-well.
-
-Incorrect example 1:
- dma_addr_t dma_handle;
-
- dma_handle = dma_map_single(dev, addr, size, direction);
- if ((dma_handle & 0xffff != 0) || (dma_handle >= 0x1000000)) {
- goto map_error;
- }
-
-Incorrect example 2:
- dma_addr_t dma_handle;
-
- dma_handle = dma_map_single(dev, addr, size, direction);
- if (dma_handle == DMA_ERROR_CODE) {
- goto map_error;
- }
-
-You should call dma_unmap_single when the DMA activity is finished, e.g.
-from the interrupt which told you that the DMA transfer is done.
-
-Using cpu pointers like this for single mappings has a disadvantage,
-you cannot reference HIGHMEM memory in this way. Thus, there is a
-map/unmap interface pair akin to dma_{map,unmap}_single. These
-interfaces deal with page/offset pairs instead of cpu pointers.
-Specifically:
-
- struct device *dev = &my_dev->dev;
- dma_addr_t dma_handle;
- struct page *page = buffer->page;
- unsigned long offset = buffer->offset;
- size_t size = buffer->len;
-
- dma_handle = dma_map_page(dev, page, offset, size, direction);
- if (dma_mapping_error(dma_handle)) {
- /*
- * reduce current DMA mapping usage,
- * delay and try again later or
- * reset driver.
- */
- goto map_error_handling;
- }
-
- ...
-
- dma_unmap_page(dev, dma_handle, size, direction);
-
-Here, "offset" means byte offset within the given page.
-
-You should call dma_mapping_error() as dma_map_page() could fail and return
-error as outlined under the dma_map_single() discussion.
-
-You should call dma_unmap_page when the DMA activity is finished, e.g.
-from the interrupt which told you that the DMA transfer is done.
-
-With scatterlists, you map a region gathered from several regions by:
-
- int i, count = dma_map_sg(dev, sglist, nents, direction);
- struct scatterlist *sg;
-
- for_each_sg(sglist, sg, count, i) {
- hw_address[i] = sg_dma_address(sg);
- hw_len[i] = sg_dma_len(sg);
- }
-
-where nents is the number of entries in the sglist.
-
-The implementation is free to merge several consecutive sglist entries
-into one (e.g. if DMA mapping is done with PAGE_SIZE granularity, any
-consecutive sglist entries can be merged into one provided the first one
-ends and the second one starts on a page boundary - in fact this is a huge
-advantage for cards which either cannot do scatter-gather or have very
-limited number of scatter-gather entries) and returns the actual number
-of sg entries it mapped them to. On failure 0 is returned.
-
-Then you should loop count times (note: this can be less than nents times)
-and use sg_dma_address() and sg_dma_len() macros where you previously
-accessed sg->address and sg->length as shown above.
-
-To unmap a scatterlist, just call:
-
- dma_unmap_sg(dev, sglist, nents, direction);
-
-Again, make sure DMA activity has already finished.
-
-PLEASE NOTE: The 'nents' argument to the dma_unmap_sg call must be
- the _same_ one you passed into the dma_map_sg call,
- it should _NOT_ be the 'count' value _returned_ from the
- dma_map_sg call.
-
-Every dma_map_{single,sg} call should have its dma_unmap_{single,sg}
-counterpart, because the bus address space is a shared resource (although
-in some ports the mapping is per each BUS so less devices contend for the
-same bus address space) and you could render the machine unusable by eating
-all bus addresses.
-
-If you need to use the same streaming DMA region multiple times and touch
-the data in between the DMA transfers, the buffer needs to be synced
-properly in order for the cpu and device to see the most uptodate and
-correct copy of the DMA buffer.
-
-So, firstly, just map it with dma_map_{single,sg}, and after each DMA
-transfer call either:
-
- dma_sync_single_for_cpu(dev, dma_handle, size, direction);
-
-or:
-
- dma_sync_sg_for_cpu(dev, sglist, nents, direction);
-
-as appropriate.
-
-Then, if you wish to let the device get at the DMA area again,
-finish accessing the data with the cpu, and then before actually
-giving the buffer to the hardware call either:
-
- dma_sync_single_for_device(dev, dma_handle, size, direction);
-
-or:
-
- dma_sync_sg_for_device(dev, sglist, nents, direction);
-
-as appropriate.
-
-After the last DMA transfer call one of the DMA unmap routines
-dma_unmap_{single,sg}. If you don't touch the data from the first dma_map_*
-call till dma_unmap_*, then you don't have to call the dma_sync_*
-routines at all.
-
-Here is pseudo code which shows a situation in which you would need
-to use the dma_sync_*() interfaces.
-
- my_card_setup_receive_buffer(struct my_card *cp, char *buffer, int len)
- {
- dma_addr_t mapping;
-
- mapping = dma_map_single(cp->dev, buffer, len, DMA_FROM_DEVICE);
- if (dma_mapping_error(dma_handle)) {
- /*
- * reduce current DMA mapping usage,
- * delay and try again later or
- * reset driver.
- */
- goto map_error_handling;
- }
-
- cp->rx_buf = buffer;
- cp->rx_len = len;
- cp->rx_dma = mapping;
-
- give_rx_buf_to_card(cp);
- }
-
- ...
-
- my_card_interrupt_handler(int irq, void *devid, struct pt_regs *regs)
- {
- struct my_card *cp = devid;
-
- ...
- if (read_card_status(cp) == RX_BUF_TRANSFERRED) {
- struct my_card_header *hp;
-
- /* Examine the header to see if we wish
- * to accept the data. But synchronize
- * the DMA transfer with the CPU first
- * so that we see updated contents.
- */
- dma_sync_single_for_cpu(&cp->dev, cp->rx_dma,
- cp->rx_len,
- DMA_FROM_DEVICE);
-
- /* Now it is safe to examine the buffer. */
- hp = (struct my_card_header *) cp->rx_buf;
- if (header_is_ok(hp)) {
- dma_unmap_single(&cp->dev, cp->rx_dma, cp->rx_len,
- DMA_FROM_DEVICE);
- pass_to_upper_layers(cp->rx_buf);
- make_and_setup_new_rx_buf(cp);
- } else {
- /* CPU should not write to
- * DMA_FROM_DEVICE-mapped area,
- * so dma_sync_single_for_device() is
- * not needed here. It would be required
- * for DMA_BIDIRECTIONAL mapping if
- * the memory was modified.
- */
- give_rx_buf_to_card(cp);
- }
- }
- }
-
-Drivers converted fully to this interface should not use virt_to_bus any
-longer, nor should they use bus_to_virt. Some drivers have to be changed a
-little bit, because there is no longer an equivalent to bus_to_virt in the
-dynamic DMA mapping scheme - you have to always store the DMA addresses
-returned by the dma_alloc_coherent, dma_pool_alloc, and dma_map_single
-calls (dma_map_sg stores them in the scatterlist itself if the platform
-supports dynamic DMA mapping in hardware) in your driver structures and/or
-in the card registers.
-
-All drivers should be using these interfaces with no exceptions. It
-is planned to completely remove virt_to_bus() and bus_to_virt() as
-they are entirely deprecated. Some ports already do not provide these
-as it is impossible to correctly support them.
-
- Handling Errors
-
-DMA address space is limited on some architectures and an allocation
-failure can be determined by:
-
-- checking if dma_alloc_coherent returns NULL or dma_map_sg returns 0
-
-- checking the returned dma_addr_t of dma_map_single and dma_map_page
- by using dma_mapping_error():
-
- dma_addr_t dma_handle;
-
- dma_handle = dma_map_single(dev, addr, size, direction);
- if (dma_mapping_error(dev, dma_handle)) {
- /*
- * reduce current DMA mapping usage,
- * delay and try again later or
- * reset driver.
- */
- goto map_error_handling;
- }
-
-- unmap pages that are already mapped, when mapping error occurs in the middle
- of a multiple page mapping attempt. These example are applicable to
- dma_map_page() as well.
-
-Example 1:
- dma_addr_t dma_handle1;
- dma_addr_t dma_handle2;
-
- dma_handle1 = dma_map_single(dev, addr, size, direction);
- if (dma_mapping_error(dev, dma_handle1)) {
- /*
- * reduce current DMA mapping usage,
- * delay and try again later or
- * reset driver.
- */
- goto map_error_handling1;
- }
- dma_handle2 = dma_map_single(dev, addr, size, direction);
- if (dma_mapping_error(dev, dma_handle2)) {
- /*
- * reduce current DMA mapping usage,
- * delay and try again later or
- * reset driver.
- */
- goto map_error_handling2;
- }
-
- ...
-
- map_error_handling2:
- dma_unmap_single(dma_handle1);
- map_error_handling1:
-
-Example 2: (if buffers are allocated in a loop, unmap all mapped buffers when
- mapping error is detected in the middle)
-
- dma_addr_t dma_addr;
- dma_addr_t array[DMA_BUFFERS];
- int save_index = 0;
-
- for (i = 0; i < DMA_BUFFERS; i++) {
-
- ...
-
- dma_addr = dma_map_single(dev, addr, size, direction);
- if (dma_mapping_error(dev, dma_addr)) {
- /*
- * reduce current DMA mapping usage,
- * delay and try again later or
- * reset driver.
- */
- goto map_error_handling;
- }
- array[i].dma_addr = dma_addr;
- save_index++;
- }
-
- ...
-
- map_error_handling:
-
- for (i = 0; i < save_index; i++) {
-
- ...
-
- dma_unmap_single(array[i].dma_addr);
- }
-
-Networking drivers must call dev_kfree_skb to free the socket buffer
-and return NETDEV_TX_OK if the DMA mapping fails on the transmit hook
-(ndo_start_xmit). This means that the socket buffer is just dropped in
-the failure case.
-
-SCSI drivers must return SCSI_MLQUEUE_HOST_BUSY if the DMA mapping
-fails in the queuecommand hook. This means that the SCSI subsystem
-passes the command to the driver again later.
-
- Optimizing Unmap State Space Consumption
-
-On many platforms, dma_unmap_{single,page}() is simply a nop.
-Therefore, keeping track of the mapping address and length is a waste
-of space. Instead of filling your drivers up with ifdefs and the like
-to "work around" this (which would defeat the whole purpose of a
-portable API) the following facilities are provided.
-
-Actually, instead of describing the macros one by one, we'll
-transform some example code.
-
-1) Use DEFINE_DMA_UNMAP_{ADDR,LEN} in state saving structures.
- Example, before:
-
- struct ring_state {
- struct sk_buff *skb;
- dma_addr_t mapping;
- __u32 len;
- };
-
- after:
-
- struct ring_state {
- struct sk_buff *skb;
- DEFINE_DMA_UNMAP_ADDR(mapping);
- DEFINE_DMA_UNMAP_LEN(len);
- };
-
-2) Use dma_unmap_{addr,len}_set to set these values.
- Example, before:
-
- ringp->mapping = FOO;
- ringp->len = BAR;
-
- after:
-
- dma_unmap_addr_set(ringp, mapping, FOO);
- dma_unmap_len_set(ringp, len, BAR);
-
-3) Use dma_unmap_{addr,len} to access these values.
- Example, before:
-
- dma_unmap_single(dev, ringp->mapping, ringp->len,
- DMA_FROM_DEVICE);
-
- after:
-
- dma_unmap_single(dev,
- dma_unmap_addr(ringp, mapping),
- dma_unmap_len(ringp, len),
- DMA_FROM_DEVICE);
-
-It really should be self-explanatory. We treat the ADDR and LEN
-separately, because it is possible for an implementation to only
-need the address in order to perform the unmap operation.
-
- Platform Issues
-
-If you are just writing drivers for Linux and do not maintain
-an architecture port for the kernel, you can safely skip down
-to "Closing".
-
-1) Struct scatterlist requirements.
-
- Don't invent the architecture specific struct scatterlist; just use
- <asm-generic/scatterlist.h>. You need to enable
- CONFIG_NEED_SG_DMA_LENGTH if the architecture supports IOMMUs
- (including software IOMMU).
-
-2) ARCH_DMA_MINALIGN
-
- Architectures must ensure that kmalloc'ed buffer is
- DMA-safe. Drivers and subsystems depend on it. If an architecture
- isn't fully DMA-coherent (i.e. hardware doesn't ensure that data in
- the CPU cache is identical to data in main memory),
- ARCH_DMA_MINALIGN must be set so that the memory allocator
- makes sure that kmalloc'ed buffer doesn't share a cache line with
- the others. See arch/arm/include/asm/cache.h as an example.
-
- Note that ARCH_DMA_MINALIGN is about DMA memory alignment
- constraints. You don't need to worry about the architecture data
- alignment constraints (e.g. the alignment constraints about 64-bit
- objects).
-
-3) Supporting multiple types of IOMMUs
-
- If your architecture needs to support multiple types of IOMMUs, you
- can use include/linux/asm-generic/dma-mapping-common.h. It's a
- library to support the DMA API with multiple types of IOMMUs. Lots
- of architectures (x86, powerpc, sh, alpha, ia64, microblaze and
- sparc) use it. Choose one to see how it can be used. If you need to
- support multiple types of IOMMUs in a single system, the example of
- x86 or powerpc helps.
-
- Closing
-
-This document, and the API itself, would not be in its current
-form without the feedback and suggestions from numerous individuals.
-We would like to specifically mention, in no particular order, the
-following people:
-
- Russell King <rmk@xxxxxxxxxxxxxxxx>
- Leo Dagum <dagum@xxxxxxxxxxxxxxxxxxx>
- Ralf Baechle <ralf@xxxxxxxxxxx>
- Grant Grundler <grundler@xxxxxxxxxx>
- Jay Estabrook <Jay.Estabrook@xxxxxxxxxx>
- Thomas Sailer <sailer@xxxxxxxxxxxxxx>
- Andrea Arcangeli <andrea@xxxxxxx>
- Jens Axboe <jens.axboe@xxxxxxxxxx>
- David Mosberger-Tang <davidm@xxxxxxxxxx>
diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
deleted file mode 100644
index e865279..0000000
--- a/Documentation/DMA-API.txt
+++ /dev/null
@@ -1,700 +0,0 @@
- Dynamic DMA mapping using the generic device
- ============================================
-
- James E.J. Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
-
-This document describes the DMA API. For a more gentle introduction
-of the API (and actual examples) see
-Documentation/DMA-API-HOWTO.txt.
-
-This API is split into two pieces. Part I describes the API. Part II
-describes the extensions to the API for supporting non-consistent
-memory machines. Unless you know that your driver absolutely has to
-support non-consistent platforms (this is usually only legacy
-platforms) you should only use the API described in part I.
-
-Part I - dma_ API
--------------------------------------
-
-To get the dma_ API, you must #include <linux/dma-mapping.h>
-
-
-Part Ia - Using large dma-coherent buffers
-------------------------------------------
-
-void *
-dma_alloc_coherent(struct device *dev, size_t size,
- dma_addr_t *dma_handle, gfp_t flag)
-
-Consistent memory is memory for which a write by either the device or
-the processor can immediately be read by the processor or device
-without having to worry about caching effects. (You may however need
-to make sure to flush the processor's write buffers before telling
-devices to read that memory.)
-
-This routine allocates a region of <size> bytes of consistent memory.
-It also returns a <dma_handle> which may be cast to an unsigned
-integer the same width as the bus and used as the physical address
-base of the region.
-
-Returns: a pointer to the allocated region (in the processor's virtual
-address space) or NULL if the allocation failed.
-
-Note: consistent memory can be expensive on some platforms, and the
-minimum allocation length may be as big as a page, so you should
-consolidate your requests for consistent memory as much as possible.
-The simplest way to do that is to use the dma_pool calls (see below).
-
-The flag parameter (dma_alloc_coherent only) allows the caller to
-specify the GFP_ flags (see kmalloc) for the allocation (the
-implementation may choose to ignore flags that affect the location of
-the returned memory, like GFP_DMA).
-
-void *
-dma_zalloc_coherent(struct device *dev, size_t size,
- dma_addr_t *dma_handle, gfp_t flag)
-
-Wraps dma_alloc_coherent() and also zeroes the returned memory if the
-allocation attempt succeeded.
-
-void
-dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
- dma_addr_t dma_handle)
-
-Free the region of consistent memory you previously allocated. dev,
-size and dma_handle must all be the same as those passed into the
-consistent allocate. cpu_addr must be the virtual address returned by
-the consistent allocate.
-
-Note that unlike their sibling allocation calls, these routines
-may only be called with IRQs enabled.
-
-
-Part Ib - Using small dma-coherent buffers
-------------------------------------------
-
-To get this part of the dma_ API, you must #include <linux/dmapool.h>
-
-Many drivers need lots of small dma-coherent memory regions for DMA
-descriptors or I/O buffers. Rather than allocating in units of a page
-or more using dma_alloc_coherent(), you can use DMA pools. These work
-much like a struct kmem_cache, except that they use the dma-coherent allocator,
-not __get_free_pages(). Also, they understand common hardware constraints
-for alignment, like queue heads needing to be aligned on N-byte boundaries.
-
-
- struct dma_pool *
- dma_pool_create(const char *name, struct device *dev,
- size_t size, size_t align, size_t alloc);
-
-The pool create() routines initialize a pool of dma-coherent buffers
-for use with a given device. It must be called in a context which
-can sleep.
-
-The "name" is for diagnostics (like a struct kmem_cache name); dev and size
-are like what you'd pass to dma_alloc_coherent(). The device's hardware
-alignment requirement for this type of data is "align" (which is expressed
-in bytes, and must be a power of two). If your device has no boundary
-crossing restrictions, pass 0 for alloc; passing 4096 says memory allocated
-from this pool must not cross 4KByte boundaries.
-
-
- void *dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags,
- dma_addr_t *dma_handle);
-
-This allocates memory from the pool; the returned memory will meet the size
-and alignment requirements specified at creation time. Pass GFP_ATOMIC to
-prevent blocking, or if it's permitted (not in_interrupt, not holding SMP locks),
-pass GFP_KERNEL to allow blocking. Like dma_alloc_coherent(), this returns
-two values: an address usable by the cpu, and the dma address usable by the
-pool's device.
-
-
- void dma_pool_free(struct dma_pool *pool, void *vaddr,
- dma_addr_t addr);
-
-This puts memory back into the pool. The pool is what was passed to
-the pool allocation routine; the cpu (vaddr) and dma addresses are what
-were returned when that routine allocated the memory being freed.
-
-
- void dma_pool_destroy(struct dma_pool *pool);
-
-The pool destroy() routines free the resources of the pool. They must be
-called in a context which can sleep. Make sure you've freed all allocated
-memory back to the pool before you destroy it.
-
-
-Part Ic - DMA addressing limitations
-------------------------------------
-
-int
-dma_supported(struct device *dev, u64 mask)
-
-Checks to see if the device can support DMA to the memory described by
-mask.
-
-Returns: 1 if it can and 0 if it can't.
-
-Notes: This routine merely tests to see if the mask is possible. It
-won't change the current mask settings. It is more intended as an
-internal API for use by the platform than an external API for use by
-driver writers.
-
-int
-dma_set_mask_and_coherent(struct device *dev, u64 mask)
-
-Checks to see if the mask is possible and updates the device
-streaming and coherent DMA mask parameters if it is.
-
-Returns: 0 if successful and a negative error if not.
-
-int
-dma_set_mask(struct device *dev, u64 mask)
-
-Checks to see if the mask is possible and updates the device
-parameters if it is.
-
-Returns: 0 if successful and a negative error if not.
-
-int
-dma_set_coherent_mask(struct device *dev, u64 mask)
-
-Checks to see if the mask is possible and updates the device
-parameters if it is.
-
-Returns: 0 if successful and a negative error if not.
-
-u64
-dma_get_required_mask(struct device *dev)
-
-This API returns the mask that the platform requires to
-operate efficiently. Usually this means the returned mask
-is the minimum required to cover all of memory. Examining the
-required mask gives drivers with variable descriptor sizes the
-opportunity to use smaller descriptors as necessary.
-
-Requesting the required mask does not alter the current mask. If you
-wish to take advantage of it, you should issue a dma_set_mask()
-call to set the mask to the value returned.
-
-
-Part Id - Streaming DMA mappings
---------------------------------
-
-dma_addr_t
-dma_map_single(struct device *dev, void *cpu_addr, size_t size,
- enum dma_data_direction direction)
-
-Maps a piece of processor virtual memory so it can be accessed by the
-device and returns the physical handle of the memory.
-
-The direction for both api's may be converted freely by casting.
-However the dma_ API uses a strongly typed enumerator for its
-direction:
-
-DMA_NONE no direction (used for debugging)
-DMA_TO_DEVICE data is going from the memory to the device
-DMA_FROM_DEVICE data is coming from the device to the memory
-DMA_BIDIRECTIONAL direction isn't known
-
-Notes: Not all memory regions in a machine can be mapped by this
-API. Further, regions that appear to be physically contiguous in
-kernel virtual space may not be contiguous as physical memory. Since
-this API does not provide any scatter/gather capability, it will fail
-if the user tries to map a non-physically contiguous piece of memory.
-For this reason, it is recommended that memory mapped by this API be
-obtained only from sources which guarantee it to be physically contiguous
-(like kmalloc).
-
-Further, the physical address of the memory must be within the
-dma_mask of the device (the dma_mask represents a bit mask of the
-addressable region for the device. I.e., if the physical address of
-the memory anded with the dma_mask is still equal to the physical
-address, then the device can perform DMA to the memory). In order to
-ensure that the memory allocated by kmalloc is within the dma_mask,
-the driver may specify various platform-dependent flags to restrict
-the physical memory range of the allocation (e.g. on x86, GFP_DMA
-guarantees to be within the first 16Mb of available physical memory,
-as required by ISA devices).
-
-Note also that the above constraints on physical contiguity and
-dma_mask may not apply if the platform has an IOMMU (a device which
-supplies a physical to virtual mapping between the I/O memory bus and
-the device). However, to be portable, device driver writers may *not*
-assume that such an IOMMU exists.
-
-Warnings: Memory coherency operates at a granularity called the cache
-line width. In order for memory mapped by this API to operate
-correctly, the mapped region must begin exactly on a cache line
-boundary and end exactly on one (to prevent two separately mapped
-regions from sharing a single cache line). Since the cache line size
-may not be known at compile time, the API will not enforce this
-requirement. Therefore, it is recommended that driver writers who
-don't take special care to determine the cache line size at run time
-only map virtual regions that begin and end on page boundaries (which
-are guaranteed also to be cache line boundaries).
-
-DMA_TO_DEVICE synchronisation must be done after the last modification
-of the memory region by the software and before it is handed off to
-the driver. Once this primitive is used, memory covered by this
-primitive should be treated as read-only by the device. If the device
-may write to it at any point, it should be DMA_BIDIRECTIONAL (see
-below).
-
-DMA_FROM_DEVICE synchronisation must be done before the driver
-accesses data that may be changed by the device. This memory should
-be treated as read-only by the driver. If the driver needs to write
-to it at any point, it should be DMA_BIDIRECTIONAL (see below).
-
-DMA_BIDIRECTIONAL requires special handling: it means that the driver
-isn't sure if the memory was modified before being handed off to the
-device and also isn't sure if the device will also modify it. Thus,
-you must always sync bidirectional memory twice: once before the
-memory is handed off to the device (to make sure all memory changes
-are flushed from the processor) and once before the data may be
-accessed after being used by the device (to make sure any processor
-cache lines are updated with data that the device may have changed).
-
-void
-dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
- enum dma_data_direction direction)
-
-Unmaps the region previously mapped. All the parameters passed in
-must be identical to those passed in (and returned) by the mapping
-API.
-
-dma_addr_t
-dma_map_page(struct device *dev, struct page *page,
- unsigned long offset, size_t size,
- enum dma_data_direction direction)
-void
-dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
- enum dma_data_direction direction)
-
-API for mapping and unmapping for pages. All the notes and warnings
-for the other mapping APIs apply here. Also, although the <offset>
-and <size> parameters are provided to do partial page mapping, it is
-recommended that you never use these unless you really know what the
-cache width is.
-
-int
-dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
-
-In some circumstances dma_map_single and dma_map_page will fail to create
-a mapping. A driver can check for these errors by testing the returned
-dma address with dma_mapping_error(). A non-zero return value means the mapping
-could not be created and the driver should take appropriate action (e.g.
-reduce current DMA mapping usage or delay and try again later).
-
- int
- dma_map_sg(struct device *dev, struct scatterlist *sg,
- int nents, enum dma_data_direction direction)
-
-Returns: the number of physical segments mapped (this may be shorter
-than <nents> passed in if some elements of the scatter/gather list are
-physically or virtually adjacent and an IOMMU maps them with a single
-entry).
-
-Please note that the sg cannot be mapped again if it has been mapped once.
-The mapping process is allowed to destroy information in the sg.
-
-As with the other mapping interfaces, dma_map_sg can fail. When it
-does, 0 is returned and a driver must take appropriate action. It is
-critical that the driver do something, in the case of a block driver
-aborting the request or even oopsing is better than doing nothing and
-corrupting the filesystem.
-
-With scatterlists, you use the resulting mapping like this:
-
- int i, count = dma_map_sg(dev, sglist, nents, direction);
- struct scatterlist *sg;
-
- for_each_sg(sglist, sg, count, i) {
- hw_address[i] = sg_dma_address(sg);
- hw_len[i] = sg_dma_len(sg);
- }
-
-where nents is the number of entries in the sglist.
-
-The implementation is free to merge several consecutive sglist entries
-into one (e.g. with an IOMMU, or if several pages just happen to be
-physically contiguous) and returns the actual number of sg entries it
-mapped them to. On failure 0, is returned.
-
-Then you should loop count times (note: this can be less than nents times)
-and use sg_dma_address() and sg_dma_len() macros where you previously
-accessed sg->address and sg->length as shown above.
-
- void
- dma_unmap_sg(struct device *dev, struct scatterlist *sg,
- int nhwentries, enum dma_data_direction direction)
-
-Unmap the previously mapped scatter/gather list. All the parameters
-must be the same as those and passed in to the scatter/gather mapping
-API.
-
-Note: <nents> must be the number you passed in, *not* the number of
-physical entries returned.
-
-void
-dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
- enum dma_data_direction direction)
-void
-dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, size_t size,
- enum dma_data_direction direction)
-void
-dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems,
- enum dma_data_direction direction)
-void
-dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nelems,
- enum dma_data_direction direction)
-
-Synchronise a single contiguous or scatter/gather mapping for the cpu
-and device. With the sync_sg API, all the parameters must be the same
-as those passed into the single mapping API. With the sync_single API,
-you can use dma_handle and size parameters that aren't identical to
-those passed into the single mapping API to do a partial sync.
-
-Notes: You must do this:
-
-- Before reading values that have been written by DMA from the device
- (use the DMA_FROM_DEVICE direction)
-- After writing values that will be written to the device using DMA
- (use the DMA_TO_DEVICE) direction
-- before *and* after handing memory to the device if the memory is
- DMA_BIDIRECTIONAL
-
-See also dma_map_single().
-
-dma_addr_t
-dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size,
- enum dma_data_direction dir,
- struct dma_attrs *attrs)
-
-void
-dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr,
- size_t size, enum dma_data_direction dir,
- struct dma_attrs *attrs)
-
-int
-dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
- int nents, enum dma_data_direction dir,
- struct dma_attrs *attrs)
-
-void
-dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl,
- int nents, enum dma_data_direction dir,
- struct dma_attrs *attrs)
-
-The four functions above are just like the counterpart functions
-without the _attrs suffixes, except that they pass an optional
-struct dma_attrs*.
-
-struct dma_attrs encapsulates a set of "dma attributes". For the
-definition of struct dma_attrs see linux/dma-attrs.h.
-
-The interpretation of dma attributes is architecture-specific, and
-each attribute should be documented in Documentation/DMA-attributes.txt.
-
-If struct dma_attrs* is NULL, the semantics of each of these
-functions is identical to those of the corresponding function
-without the _attrs suffix. As a result dma_map_single_attrs()
-can generally replace dma_map_single(), etc.
-
-As an example of the use of the *_attrs functions, here's how
-you could pass an attribute DMA_ATTR_FOO when mapping memory
-for DMA:
-
-#include <linux/dma-attrs.h>
-/* DMA_ATTR_FOO should be defined in linux/dma-attrs.h and
- * documented in Documentation/DMA-attributes.txt */
-...
-
- DEFINE_DMA_ATTRS(attrs);
- dma_set_attr(DMA_ATTR_FOO, &attrs);
- ....
- n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, &attr);
- ....
-
-Architectures that care about DMA_ATTR_FOO would check for its
-presence in their implementations of the mapping and unmapping
-routines, e.g.:
-
-void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr,
- size_t size, enum dma_data_direction dir,
- struct dma_attrs *attrs)
-{
- ....
- int foo = dma_get_attr(DMA_ATTR_FOO, attrs);
- ....
- if (foo)
- /* twizzle the frobnozzle */
- ....
-
-
-Part II - Advanced dma_ usage
------------------------------
-
-Warning: These pieces of the DMA API should not be used in the
-majority of cases, since they cater for unlikely corner cases that
-don't belong in usual drivers.
-
-If you don't understand how cache line coherency works between a
-processor and an I/O device, you should not be using this part of the
-API at all.
-
-void *
-dma_alloc_noncoherent(struct device *dev, size_t size,
- dma_addr_t *dma_handle, gfp_t flag)
-
-Identical to dma_alloc_coherent() except that the platform will
-choose to return either consistent or non-consistent memory as it sees
-fit. By using this API, you are guaranteeing to the platform that you
-have all the correct and necessary sync points for this memory in the
-driver should it choose to return non-consistent memory.
-
-Note: where the platform can return consistent memory, it will
-guarantee that the sync points become nops.
-
-Warning: Handling non-consistent memory is a real pain. You should
-only ever use this API if you positively know your driver will be
-required to work on one of the rare (usually non-PCI) architectures
-that simply cannot make consistent memory.
-
-void
-dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr,
- dma_addr_t dma_handle)
-
-Free memory allocated by the nonconsistent API. All parameters must
-be identical to those passed in (and returned by
-dma_alloc_noncoherent()).
-
-int
-dma_get_cache_alignment(void)
-
-Returns the processor cache alignment. This is the absolute minimum
-alignment *and* width that you must observe when either mapping
-memory or doing partial flushes.
-
-Notes: This API may return a number *larger* than the actual cache
-line, but it will guarantee that one or more cache lines fit exactly
-into the width returned by this call. It will also always be a power
-of two for easy alignment.
-
-void
-dma_cache_sync(struct device *dev, void *vaddr, size_t size,
- enum dma_data_direction direction)
-
-Do a partial sync of memory that was allocated by
-dma_alloc_noncoherent(), starting at virtual address vaddr and
-continuing on for size. Again, you *must* observe the cache line
-boundaries when doing this.
-
-int
-dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr,
- dma_addr_t device_addr, size_t size, int
- flags)
-
-Declare region of memory to be handed out by dma_alloc_coherent when
-it's asked for coherent memory for this device.
-
-bus_addr is the physical address to which the memory is currently
-assigned in the bus responding region (this will be used by the
-platform to perform the mapping).
-
-device_addr is the physical address the device needs to be programmed
-with actually to address this memory (this will be handed out as the
-dma_addr_t in dma_alloc_coherent()).
-
-size is the size of the area (must be multiples of PAGE_SIZE).
-
-flags can be or'd together and are:
-
-DMA_MEMORY_MAP - request that the memory returned from
-dma_alloc_coherent() be directly writable.
-
-DMA_MEMORY_IO - request that the memory returned from
-dma_alloc_coherent() be addressable using read/write/memcpy_toio etc.
-
-One or both of these flags must be present.
-
-DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by
-dma_alloc_coherent of any child devices of this one (for memory residing
-on a bridge).
-
-DMA_MEMORY_EXCLUSIVE - only allocate memory from the declared regions.
-Do not allow dma_alloc_coherent() to fall back to system memory when
-it's out of memory in the declared region.
-
-The return value will be either DMA_MEMORY_MAP or DMA_MEMORY_IO and
-must correspond to a passed in flag (i.e. no returning DMA_MEMORY_IO
-if only DMA_MEMORY_MAP were passed in) for success or zero for
-failure.
-
-Note, for DMA_MEMORY_IO returns, all subsequent memory returned by
-dma_alloc_coherent() may no longer be accessed directly, but instead
-must be accessed using the correct bus functions. If your driver
-isn't prepared to handle this contingency, it should not specify
-DMA_MEMORY_IO in the input flags.
-
-As a simplification for the platforms, only *one* such region of
-memory may be declared per device.
-
-For reasons of efficiency, most platforms choose to track the declared
-region only at the granularity of a page. For smaller allocations,
-you should use the dma_pool() API.
-
-void
-dma_release_declared_memory(struct device *dev)
-
-Remove the memory region previously declared from the system. This
-API performs *no* in-use checking for this region and will return
-unconditionally having removed all the required structures. It is the
-driver's job to ensure that no parts of this memory region are
-currently in use.
-
-void *
-dma_mark_declared_memory_occupied(struct device *dev,
- dma_addr_t device_addr, size_t size)
-
-This is used to occupy specific regions of the declared space
-(dma_alloc_coherent() will hand out the first free region it finds).
-
-device_addr is the *device* address of the region requested.
-
-size is the size (and should be a page-sized multiple).
-
-The return value will be either a pointer to the processor virtual
-address of the memory, or an error (via PTR_ERR()) if any part of the
-region is occupied.
-
-Part III - Debug drivers use of the DMA-API
--------------------------------------------
-
-The DMA-API as described above as some constraints. DMA addresses must be
-released with the corresponding function with the same size for example. With
-the advent of hardware IOMMUs it becomes more and more important that drivers
-do not violate those constraints. In the worst case such a violation can
-result in data corruption up to destroyed filesystems.
-
-To debug drivers and find bugs in the usage of the DMA-API checking code can
-be compiled into the kernel which will tell the developer about those
-violations. If your architecture supports it you can select the "Enable
-debugging of DMA-API usage" option in your kernel configuration. Enabling this
-option has a performance impact. Do not enable it in production kernels.
-
-If you boot the resulting kernel will contain code which does some bookkeeping
-about what DMA memory was allocated for which device. If this code detects an
-error it prints a warning message with some details into your kernel log. An
-example warning message may look like this:
-
-------------[ cut here ]------------
-WARNING: at /data2/repos/linux-2.6-iommu/lib/dma-debug.c:448
- check_unmap+0x203/0x490()
-Hardware name:
-forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong
- function [device address=0x00000000640444be] [size=66 bytes] [mapped as
-single] [unmapped as page]
-Modules linked in: nfsd exportfs bridge stp llc r8169
-Pid: 0, comm: swapper Tainted: G W 2.6.28-dmatest-09289-g8bb99c0 #1
-Call Trace:
- <IRQ> [<ffffffff80240b22>] warn_slowpath+0xf2/0x130
- [<ffffffff80647b70>] _spin_unlock+0x10/0x30
- [<ffffffff80537e75>] usb_hcd_link_urb_to_ep+0x75/0xc0
- [<ffffffff80647c22>] _spin_unlock_irqrestore+0x12/0x40
- [<ffffffff8055347f>] ohci_urb_enqueue+0x19f/0x7c0
- [<ffffffff80252f96>] queue_work+0x56/0x60
- [<ffffffff80237e10>] enqueue_task_fair+0x20/0x50
- [<ffffffff80539279>] usb_hcd_submit_urb+0x379/0xbc0
- [<ffffffff803b78c3>] cpumask_next_and+0x23/0x40
- [<ffffffff80235177>] find_busiest_group+0x207/0x8a0
- [<ffffffff8064784f>] _spin_lock_irqsave+0x1f/0x50
- [<ffffffff803c7ea3>] check_unmap+0x203/0x490
- [<ffffffff803c8259>] debug_dma_unmap_page+0x49/0x50
- [<ffffffff80485f26>] nv_tx_done_optimized+0xc6/0x2c0
- [<ffffffff80486c13>] nv_nic_irq_optimized+0x73/0x2b0
- [<ffffffff8026df84>] handle_IRQ_event+0x34/0x70
- [<ffffffff8026ffe9>] handle_edge_irq+0xc9/0x150
- [<ffffffff8020e3ab>] do_IRQ+0xcb/0x1c0
- [<ffffffff8020c093>] ret_from_intr+0x0/0xa
- <EOI> <4>---[ end trace f6435a98e2a38c0e ]---
-
-The driver developer can find the driver and the device including a stacktrace
-of the DMA-API call which caused this warning.
-
-Per default only the first error will result in a warning message. All other
-errors will only silently counted. This limitation exist to prevent the code
-from flooding your kernel log. To support debugging a device driver this can
-be disabled via debugfs. See the debugfs interface documentation below for
-details.
-
-The debugfs directory for the DMA-API debugging code is called dma-api/. In
-this directory the following files can currently be found:
-
- dma-api/all_errors This file contains a numeric value. If this
- value is not equal to zero the debugging code
- will print a warning for every error it finds
- into the kernel log. Be careful with this
- option, as it can easily flood your logs.
-
- dma-api/disabled This read-only file contains the character 'Y'
- if the debugging code is disabled. This can
- happen when it runs out of memory or if it was
- disabled at boot time
-
- dma-api/error_count This file is read-only and shows the total
- numbers of errors found.
-
- dma-api/num_errors The number in this file shows how many
- warnings will be printed to the kernel log
- before it stops. This number is initialized to
- one at system boot and be set by writing into
- this file
-
- dma-api/min_free_entries
- This read-only file can be read to get the
- minimum number of free dma_debug_entries the
- allocator has ever seen. If this value goes
- down to zero the code will disable itself
- because it is not longer reliable.
-
- dma-api/num_free_entries
- The current number of free dma_debug_entries
- in the allocator.
-
- dma-api/driver-filter
- You can write a name of a driver into this file
- to limit the debug output to requests from that
- particular driver. Write an empty string to
- that file to disable the filter and see
- all errors again.
-
-If you have this code compiled into your kernel it will be enabled by default.
-If you want to boot without the bookkeeping anyway you can provide
-'dma_debug=off' as a boot parameter. This will disable DMA-API debugging.
-Notice that you can not enable it again at runtime. You have to reboot to do
-so.
-
-If you want to see debug messages only for a special device driver you can
-specify the dma_debug_driver=<drivername> parameter. This will enable the
-driver filter at boot time. The debug code will only print errors for that
-driver afterwards. This filter can be disabled or changed later using debugfs.
-
-When the code disables itself at runtime this is most likely because it ran
-out of dma_debug_entries. These entries are preallocated at boot. The number
-of preallocated entries is defined per architecture. If it is too low for you
-boot with 'dma_debug_entries=<your_desired_number>' to overwrite the
-architectural default.
-
-void debug_dmap_mapping_error(struct device *dev, dma_addr_t dma_addr);
-
-dma-debug interface debug_dma_mapping_error() to debug drivers that fail
-to check dma mapping errors on addresses returned by dma_map_single() and
-dma_map_page() interfaces. This interface clears a flag set by
-debug_dma_map_page() to indicate that dma_mapping_error() has been called by
-the driver. When driver does unmap, debug_dma_unmap() checks the flag and if
-this flag is still set, prints warning message that includes call trace that
-leads up to the unmap. This interface can be called from dma_mapping_error()
-routines to enable dma mapping error check debugging.
-
diff --git a/Documentation/DMA-ISA-LPC.txt b/Documentation/DMA-ISA-LPC.txt
deleted file mode 100644
index e767805..0000000
--- a/Documentation/DMA-ISA-LPC.txt
+++ /dev/null
@@ -1,151 +0,0 @@
- DMA with ISA and LPC devices
- ============================
-
- Pierre Ossman <drzeus@xxxxxxxxx>
-
-This document describes how to do DMA transfers using the old ISA DMA
-controller. Even though ISA is more or less dead today the LPC bus
-uses the same DMA system so it will be around for quite some time.
-
-Part I - Headers and dependencies
----------------------------------
-
-To do ISA style DMA you need to include two headers:
-
-#include <linux/dma-mapping.h>
-#include <asm/dma.h>
-
-The first is the generic DMA API used to convert virtual addresses to
-physical addresses (see Documentation/DMA-API.txt for details).
-
-The second contains the routines specific to ISA DMA transfers. Since
-this is not present on all platforms make sure you construct your
-Kconfig to be dependent on ISA_DMA_API (not ISA) so that nobody tries
-to build your driver on unsupported platforms.
-
-Part II - Buffer allocation
----------------------------
-
-The ISA DMA controller has some very strict requirements on which
-memory it can access so extra care must be taken when allocating
-buffers.
-
-(You usually need a special buffer for DMA transfers instead of
-transferring directly to and from your normal data structures.)
-
-The DMA-able address space is the lowest 16 MB of _physical_ memory.
-Also the transfer block may not cross page boundaries (which are 64
-or 128 KiB depending on which channel you use).
-
-In order to allocate a piece of memory that satisfies all these
-requirements you pass the flag GFP_DMA to kmalloc.
-
-Unfortunately the memory available for ISA DMA is scarce so unless you
-allocate the memory during boot-up it's a good idea to also pass
-__GFP_REPEAT and __GFP_NOWARN to make the allocater try a bit harder.
-
-(This scarcity also means that you should allocate the buffer as
-early as possible and not release it until the driver is unloaded.)
-
-Part III - Address translation
-------------------------------
-
-To translate the virtual address to a physical use the normal DMA
-API. Do _not_ use isa_virt_to_phys() even though it does the same
-thing. The reason for this is that the function isa_virt_to_phys()
-will require a Kconfig dependency to ISA, not just ISA_DMA_API which
-is really all you need. Remember that even though the DMA controller
-has its origins in ISA it is used elsewhere.
-
-Note: x86_64 had a broken DMA API when it came to ISA but has since
-been fixed. If your arch has problems then fix the DMA API instead of
-reverting to the ISA functions.
-
-Part IV - Channels
-------------------
-
-A normal ISA DMA controller has 8 channels. The lower four are for
-8-bit transfers and the upper four are for 16-bit transfers.
-
-(Actually the DMA controller is really two separate controllers where
-channel 4 is used to give DMA access for the second controller (0-3).
-This means that of the four 16-bits channels only three are usable.)
-
-You allocate these in a similar fashion as all basic resources:
-
-extern int request_dma(unsigned int dmanr, const char * device_id);
-extern void free_dma(unsigned int dmanr);
-
-The ability to use 16-bit or 8-bit transfers is _not_ up to you as a
-driver author but depends on what the hardware supports. Check your
-specs or test different channels.
-
-Part V - Transfer data
-----------------------
-
-Now for the good stuff, the actual DMA transfer. :)
-
-Before you use any ISA DMA routines you need to claim the DMA lock
-using claim_dma_lock(). The reason is that some DMA operations are
-not atomic so only one driver may fiddle with the registers at a
-time.
-
-The first time you use the DMA controller you should call
-clear_dma_ff(). This clears an internal register in the DMA
-controller that is used for the non-atomic operations. As long as you
-(and everyone else) uses the locking functions then you only need to
-reset this once.
-
-Next, you tell the controller in which direction you intend to do the
-transfer using set_dma_mode(). Currently you have the options
-DMA_MODE_READ and DMA_MODE_WRITE.
-
-Set the address from where the transfer should start (this needs to
-be 16-bit aligned for 16-bit transfers) and how many bytes to
-transfer. Note that it's _bytes_. The DMA routines will do all the
-required translation to values that the DMA controller understands.
-
-The final step is enabling the DMA channel and releasing the DMA
-lock.
-
-Once the DMA transfer is finished (or timed out) you should disable
-the channel again. You should also check get_dma_residue() to make
-sure that all data has been transferred.
-
-Example:
-
-int flags, residue;
-
-flags = claim_dma_lock();
-
-clear_dma_ff();
-
-set_dma_mode(channel, DMA_MODE_WRITE);
-set_dma_addr(channel, phys_addr);
-set_dma_count(channel, num_bytes);
-
-dma_enable(channel);
-
-release_dma_lock(flags);
-
-while (!device_done());
-
-flags = claim_dma_lock();
-
-dma_disable(channel);
-
-residue = dma_get_residue(channel);
-if (residue != 0)
- printk(KERN_ERR "driver: Incomplete DMA transfer!"
- " %d bytes left!\n", residue);
-
-release_dma_lock(flags);
-
-Part VI - Suspend/resume
-------------------------
-
-It is the driver's responsibility to make sure that the machine isn't
-suspended while a DMA transfer is in progress. Also, all DMA settings
-are lost when the system suspends so if your driver relies on the DMA
-controller being in a certain state then you have to restore these
-registers upon resume.
diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
deleted file mode 100644
index cc2450d..0000000
--- a/Documentation/DMA-attributes.txt
+++ /dev/null
@@ -1,102 +0,0 @@
- DMA attributes
- ==============
-
-This document describes the semantics of the DMA attributes that are
-defined in linux/dma-attrs.h.
-
-DMA_ATTR_WRITE_BARRIER
-----------------------
-
-DMA_ATTR_WRITE_BARRIER is a (write) barrier attribute for DMA. DMA
-to a memory region with the DMA_ATTR_WRITE_BARRIER attribute forces
-all pending DMA writes to complete, and thus provides a mechanism to
-strictly order DMA from a device across all intervening busses and
-bridges. This barrier is not specific to a particular type of
-interconnect, it applies to the system as a whole, and so its
-implementation must account for the idiosyncrasies of the system all
-the way from the DMA device to memory.
-
-As an example of a situation where DMA_ATTR_WRITE_BARRIER would be
-useful, suppose that a device does a DMA write to indicate that data is
-ready and available in memory. The DMA of the "completion indication"
-could race with data DMA. Mapping the memory used for completion
-indications with DMA_ATTR_WRITE_BARRIER would prevent the race.
-
-DMA_ATTR_WEAK_ORDERING
-----------------------
-
-DMA_ATTR_WEAK_ORDERING specifies that reads and writes to the mapping
-may be weakly ordered, that is that reads and writes may pass each other.
-
-Since it is optional for platforms to implement DMA_ATTR_WEAK_ORDERING,
-those that do not will simply ignore the attribute and exhibit default
-behavior.
-
-DMA_ATTR_WRITE_COMBINE
-----------------------
-
-DMA_ATTR_WRITE_COMBINE specifies that writes to the mapping may be
-buffered to improve performance.
-
-Since it is optional for platforms to implement DMA_ATTR_WRITE_COMBINE,
-those that do not will simply ignore the attribute and exhibit default
-behavior.
-
-DMA_ATTR_NON_CONSISTENT
------------------------
-
-DMA_ATTR_NON_CONSISTENT lets the platform to choose to return either
-consistent or non-consistent memory as it sees fit. By using this API,
-you are guaranteeing to the platform that you have all the correct and
-necessary sync points for this memory in the driver.
-
-DMA_ATTR_NO_KERNEL_MAPPING
---------------------------
-
-DMA_ATTR_NO_KERNEL_MAPPING lets the platform to avoid creating a kernel
-virtual mapping for the allocated buffer. On some architectures creating
-such mapping is non-trivial task and consumes very limited resources
-(like kernel virtual address space or dma consistent address space).
-Buffers allocated with this attribute can be only passed to user space
-by calling dma_mmap_attrs(). By using this API, you are guaranteeing
-that you won't dereference the pointer returned by dma_alloc_attr(). You
-can treat it as a cookie that must be passed to dma_mmap_attrs() and
-dma_free_attrs(). Make sure that both of these also get this attribute
-set on each call.
-
-Since it is optional for platforms to implement
-DMA_ATTR_NO_KERNEL_MAPPING, those that do not will simply ignore the
-attribute and exhibit default behavior.
-
-DMA_ATTR_SKIP_CPU_SYNC
-----------------------
-
-By default dma_map_{single,page,sg} functions family transfer a given
-buffer from CPU domain to device domain. Some advanced use cases might
-require sharing a buffer between more than one device. This requires
-having a mapping created separately for each device and is usually
-performed by calling dma_map_{single,page,sg} function more than once
-for the given buffer with device pointer to each device taking part in
-the buffer sharing. The first call transfers a buffer from 'CPU' domain
-to 'device' domain, what synchronizes CPU caches for the given region
-(usually it means that the cache has been flushed or invalidated
-depending on the dma direction). However, next calls to
-dma_map_{single,page,sg}() for other devices will perform exactly the
-same synchronization operation on the CPU cache. CPU cache synchronization
-might be a time consuming operation, especially if the buffers are
-large, so it is highly recommended to avoid it if possible.
-DMA_ATTR_SKIP_CPU_SYNC allows platform code to skip synchronization of
-the CPU cache for the given buffer assuming that it has been already
-transferred to 'device' domain. This attribute can be also used for
-dma_unmap_{single,page,sg} functions family to force buffer to stay in
-device domain after releasing a mapping for it. Use this attribute with
-care!
-
-DMA_ATTR_FORCE_CONTIGUOUS
--------------------------
-
-By default DMA-mapping subsystem is allowed to assemble the buffer
-allocated by dma_alloc_attrs() function from individual pages if it can
-be mapped as contiguous chunk into device dma address space. By
-specifing this attribute the allocated buffer is forced to be contiguous
-also in physical memory.
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
deleted file mode 100644
index 505e711..0000000
--- a/Documentation/dma-buf-sharing.txt
+++ /dev/null
@@ -1,462 +0,0 @@
- DMA Buffer Sharing API Guide
- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
- Sumit Semwal
- <sumit dot semwal at linaro dot org>
- <sumit dot semwal at ti dot com>
-
-This document serves as a guide to device-driver writers on what is the dma-buf
-buffer sharing API, how to use it for exporting and using shared buffers.
-
-Any device driver which wishes to be a part of DMA buffer sharing, can do so as
-either the 'exporter' of buffers, or the 'user' of buffers.
-
-Say a driver A wants to use buffers created by driver B, then we call B as the
-exporter, and A as buffer-user.
-
-The exporter
-- implements and manages operations[1] for the buffer
-- allows other users to share the buffer by using dma_buf sharing APIs,
-- manages the details of buffer allocation,
-- decides about the actual backing storage where this allocation happens,
-- takes care of any migration of scatterlist - for all (shared) users of this
- buffer,
-
-The buffer-user
-- is one of (many) sharing users of the buffer.
-- doesn't need to worry about how the buffer is allocated, or where.
-- needs a mechanism to get access to the scatterlist that makes up this buffer
- in memory, mapped into its own address space, so it can access the same area
- of memory.
-
-dma-buf operations for device dma only
---------------------------------------
-
-The dma_buf buffer sharing API usage contains the following steps:
-
-1. Exporter announces that it wishes to export a buffer
-2. Userspace gets the file descriptor associated with the exported buffer, and
- passes it around to potential buffer-users based on use case
-3. Each buffer-user 'connects' itself to the buffer
-4. When needed, buffer-user requests access to the buffer from exporter
-5. When finished with its use, the buffer-user notifies end-of-DMA to exporter
-6. when buffer-user is done using this buffer completely, it 'disconnects'
- itself from the buffer.
-
-
-1. Exporter's announcement of buffer export
-
- The buffer exporter announces its wish to export a buffer. In this, it
- connects its own private buffer data, provides implementation for operations
- that can be performed on the exported dma_buf, and flags for the file
- associated with this buffer.
-
- Interface:
- struct dma_buf *dma_buf_export_named(void *priv, struct dma_buf_ops *ops,
- size_t size, int flags,
- const char *exp_name)
-
- If this succeeds, dma_buf_export allocates a dma_buf structure, and returns a
- pointer to the same. It also associates an anonymous file with this buffer,
- so it can be exported. On failure to allocate the dma_buf object, it returns
- NULL.
-
- 'exp_name' is the name of exporter - to facilitate information while
- debugging.
-
- Exporting modules which do not wish to provide any specific name may use the
- helper define 'dma_buf_export()', with the same arguments as above, but
- without the last argument; a __FILE__ pre-processor directive will be
- inserted in place of 'exp_name' instead.
-
-2. Userspace gets a handle to pass around to potential buffer-users
-
- Userspace entity requests for a file-descriptor (fd) which is a handle to the
- anonymous file associated with the buffer. It can then share the fd with other
- drivers and/or processes.
-
- Interface:
- int dma_buf_fd(struct dma_buf *dmabuf)
-
- This API installs an fd for the anonymous file associated with this buffer;
- returns either 'fd', or error.
-
-3. Each buffer-user 'connects' itself to the buffer
-
- Each buffer-user now gets a reference to the buffer, using the fd passed to
- it.
-
- Interface:
- struct dma_buf *dma_buf_get(int fd)
-
- This API will return a reference to the dma_buf, and increment refcount for
- it.
-
- After this, the buffer-user needs to attach its device with the buffer, which
- helps the exporter to know of device buffer constraints.
-
- Interface:
- struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
- struct device *dev)
-
- This API returns reference to an attachment structure, which is then used
- for scatterlist operations. It will optionally call the 'attach' dma_buf
- operation, if provided by the exporter.
-
- The dma-buf sharing framework does the bookkeeping bits related to managing
- the list of all attachments to a buffer.
-
-Until this stage, the buffer-exporter has the option to choose not to actually
-allocate the backing storage for this buffer, but wait for the first buffer-user
-to request use of buffer for allocation.
-
-
-4. When needed, buffer-user requests access to the buffer
-
- Whenever a buffer-user wants to use the buffer for any DMA, it asks for
- access to the buffer using dma_buf_map_attachment API. At least one attach to
- the buffer must have happened before map_dma_buf can be called.
-
- Interface:
- struct sg_table * dma_buf_map_attachment(struct dma_buf_attachment *,
- enum dma_data_direction);
-
- This is a wrapper to dma_buf->ops->map_dma_buf operation, which hides the
- "dma_buf->ops->" indirection from the users of this interface.
-
- In struct dma_buf_ops, map_dma_buf is defined as
- struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *,
- enum dma_data_direction);
-
- It is one of the buffer operations that must be implemented by the exporter.
- It should return the sg_table containing scatterlist for this buffer, mapped
- into caller's address space.
-
- If this is being called for the first time, the exporter can now choose to
- scan through the list of attachments for this buffer, collate the requirements
- of the attached devices, and choose an appropriate backing storage for the
- buffer.
-
- Based on enum dma_data_direction, it might be possible to have multiple users
- accessing at the same time (for reading, maybe), or any other kind of sharing
- that the exporter might wish to make available to buffer-users.
-
- map_dma_buf() operation can return -EINTR if it is interrupted by a signal.
-
-
-5. When finished, the buffer-user notifies end-of-DMA to exporter
-
- Once the DMA for the current buffer-user is over, it signals 'end-of-DMA' to
- the exporter using the dma_buf_unmap_attachment API.
-
- Interface:
- void dma_buf_unmap_attachment(struct dma_buf_attachment *,
- struct sg_table *);
-
- This is a wrapper to dma_buf->ops->unmap_dma_buf() operation, which hides the
- "dma_buf->ops->" indirection from the users of this interface.
-
- In struct dma_buf_ops, unmap_dma_buf is defined as
- void (*unmap_dma_buf)(struct dma_buf_attachment *, struct sg_table *);
-
- unmap_dma_buf signifies the end-of-DMA for the attachment provided. Like
- map_dma_buf, this API also must be implemented by the exporter.
-
-
-6. when buffer-user is done using this buffer, it 'disconnects' itself from the
- buffer.
-
- After the buffer-user has no more interest in using this buffer, it should
- disconnect itself from the buffer:
-
- - it first detaches itself from the buffer.
-
- Interface:
- void dma_buf_detach(struct dma_buf *dmabuf,
- struct dma_buf_attachment *dmabuf_attach);
-
- This API removes the attachment from the list in dmabuf, and optionally calls
- dma_buf->ops->detach(), if provided by exporter, for any housekeeping bits.
-
- - Then, the buffer-user returns the buffer reference to exporter.
-
- Interface:
- void dma_buf_put(struct dma_buf *dmabuf);
-
- This API then reduces the refcount for this buffer.
-
- If, as a result of this call, the refcount becomes 0, the 'release' file
- operation related to this fd is called. It calls the dmabuf->ops->release()
- operation in turn, and frees the memory allocated for dmabuf when exported.
-
-NOTES:
-- Importance of attach-detach and {map,unmap}_dma_buf operation pairs
- The attach-detach calls allow the exporter to figure out backing-storage
- constraints for the currently-interested devices. This allows preferential
- allocation, and/or migration of pages across different types of storage
- available, if possible.
-
- Bracketing of DMA access with {map,unmap}_dma_buf operations is essential
- to allow just-in-time backing of storage, and migration mid-way through a
- use-case.
-
-- Migration of backing storage if needed
- If after
- - at least one map_dma_buf has happened,
- - and the backing storage has been allocated for this buffer,
- another new buffer-user intends to attach itself to this buffer, it might
- be allowed, if possible for the exporter.
-
- In case it is allowed by the exporter:
- if the new buffer-user has stricter 'backing-storage constraints', and the
- exporter can handle these constraints, the exporter can just stall on the
- map_dma_buf until all outstanding access is completed (as signalled by
- unmap_dma_buf).
- Once all users have finished accessing and have unmapped this buffer, the
- exporter could potentially move the buffer to the stricter backing-storage,
- and then allow further {map,unmap}_dma_buf operations from any buffer-user
- from the migrated backing-storage.
-
- If the exporter cannot fulfil the backing-storage constraints of the new
- buffer-user device as requested, dma_buf_attach() would return an error to
- denote non-compatibility of the new buffer-sharing request with the current
- buffer.
-
- If the exporter chooses not to allow an attach() operation once a
- map_dma_buf() API has been called, it simply returns an error.
-
-Kernel cpu access to a dma-buf buffer object
---------------------------------------------
-
-The motivation to allow cpu access from the kernel to a dma-buf object from the
-importers side are:
-- fallback operations, e.g. if the devices is connected to a usb bus and the
- kernel needs to shuffle the data around first before sending it away.
-- full transparency for existing users on the importer side, i.e. userspace
- should not notice the difference between a normal object from that subsystem
- and an imported one backed by a dma-buf. This is really important for drm
- opengl drivers that expect to still use all the existing upload/download
- paths.
-
-Access to a dma_buf from the kernel context involves three steps:
-
-1. Prepare access, which invalidate any necessary caches and make the object
- available for cpu access.
-2. Access the object page-by-page with the dma_buf map apis
-3. Finish access, which will flush any necessary cpu caches and free reserved
- resources.
-
-1. Prepare access
-
- Before an importer can access a dma_buf object with the cpu from the kernel
- context, it needs to notify the exporter of the access that is about to
- happen.
-
- Interface:
- int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
- size_t start, size_t len,
- enum dma_data_direction direction)
-
- This allows the exporter to ensure that the memory is actually available for
- cpu access - the exporter might need to allocate or swap-in and pin the
- backing storage. The exporter also needs to ensure that cpu access is
- coherent for the given range and access direction. The range and access
- direction can be used by the exporter to optimize the cache flushing, i.e.
- access outside of the range or with a different direction (read instead of
- write) might return stale or even bogus data (e.g. when the exporter needs to
- copy the data to temporary storage).
-
- This step might fail, e.g. in oom conditions.
-
-2. Accessing the buffer
-
- To support dma_buf objects residing in highmem cpu access is page-based using
- an api similar to kmap. Accessing a dma_buf is done in aligned chunks of
- PAGE_SIZE size. Before accessing a chunk it needs to be mapped, which returns
- a pointer in kernel virtual address space. Afterwards the chunk needs to be
- unmapped again. There is no limit on how often a given chunk can be mapped
- and unmapped, i.e. the importer does not need to call begin_cpu_access again
- before mapping the same chunk again.
-
- Interfaces:
- void *dma_buf_kmap(struct dma_buf *, unsigned long);
- void dma_buf_kunmap(struct dma_buf *, unsigned long, void *);
-
- There are also atomic variants of these interfaces. Like for kmap they
- facilitate non-blocking fast-paths. Neither the importer nor the exporter (in
- the callback) is allowed to block when using these.
-
- Interfaces:
- void *dma_buf_kmap_atomic(struct dma_buf *, unsigned long);
- void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long, void *);
-
- For importers all the restrictions of using kmap apply, like the limited
- supply of kmap_atomic slots. Hence an importer shall only hold onto at most 2
- atomic dma_buf kmaps at the same time (in any given process context).
-
- dma_buf kmap calls outside of the range specified in begin_cpu_access are
- undefined. If the range is not PAGE_SIZE aligned, kmap needs to succeed on
- the partial chunks at the beginning and end but may return stale or bogus
- data outside of the range (in these partial chunks).
-
- Note that these calls need to always succeed. The exporter needs to complete
- any preparations that might fail in begin_cpu_access.
-
- For some cases the overhead of kmap can be too high, a vmap interface
- is introduced. This interface should be used very carefully, as vmalloc
- space is a limited resources on many architectures.
-
- Interfaces:
- void *dma_buf_vmap(struct dma_buf *dmabuf)
- void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
-
- The vmap call can fail if there is no vmap support in the exporter, or if it
- runs out of vmalloc space. Fallback to kmap should be implemented. Note that
- the dma-buf layer keeps a reference count for all vmap access and calls down
- into the exporter's vmap function only when no vmapping exists, and only
- unmaps it once. Protection against concurrent vmap/vunmap calls is provided
- by taking the dma_buf->lock mutex.
-
-3. Finish access
-
- When the importer is done accessing the range specified in begin_cpu_access,
- it needs to announce this to the exporter (to facilitate cache flushing and
- unpinning of any pinned resources). The result of any dma_buf kmap calls
- after end_cpu_access is undefined.
-
- Interface:
- void dma_buf_end_cpu_access(struct dma_buf *dma_buf,
- size_t start, size_t len,
- enum dma_data_direction dir);
-
-
-Direct Userspace Access/mmap Support
-------------------------------------
-
-Being able to mmap an export dma-buf buffer object has 2 main use-cases:
-- CPU fallback processing in a pipeline and
-- supporting existing mmap interfaces in importers.
-
-1. CPU fallback processing in a pipeline
-
- In many processing pipelines it is sometimes required that the cpu can access
- the data in a dma-buf (e.g. for thumbnail creation, snapshots, ...). To avoid
- the need to handle this specially in userspace frameworks for buffer sharing
- it's ideal if the dma_buf fd itself can be used to access the backing storage
- from userspace using mmap.
-
- Furthermore Android's ION framework already supports this (and is otherwise
- rather similar to dma-buf from a userspace consumer side with using fds as
- handles, too). So it's beneficial to support this in a similar fashion on
- dma-buf to have a good transition path for existing Android userspace.
-
- No special interfaces, userspace simply calls mmap on the dma-buf fd.
-
-2. Supporting existing mmap interfaces in exporters
-
- Similar to the motivation for kernel cpu access it is again important that
- the userspace code of a given importing subsystem can use the same interfaces
- with a imported dma-buf buffer object as with a native buffer object. This is
- especially important for drm where the userspace part of contemporary OpenGL,
- X, and other drivers is huge, and reworking them to use a different way to
- mmap a buffer rather invasive.
-
- The assumption in the current dma-buf interfaces is that redirecting the
- initial mmap is all that's needed. A survey of some of the existing
- subsystems shows that no driver seems to do any nefarious thing like syncing
- up with outstanding asynchronous processing on the device or allocating
- special resources at fault time. So hopefully this is good enough, since
- adding interfaces to intercept pagefaults and allow pte shootdowns would
- increase the complexity quite a bit.
-
- Interface:
- int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
- unsigned long);
-
- If the importing subsystem simply provides a special-purpose mmap call to set
- up a mapping in userspace, calling do_mmap with dma_buf->file will equally
- achieve that for a dma-buf object.
-
-3. Implementation notes for exporters
-
- Because dma-buf buffers have invariant size over their lifetime, the dma-buf
- core checks whether a vma is too large and rejects such mappings. The
- exporter hence does not need to duplicate this check.
-
- Because existing importing subsystems might presume coherent mappings for
- userspace, the exporter needs to set up a coherent mapping. If that's not
- possible, it needs to fake coherency by manually shooting down ptes when
- leaving the cpu domain and flushing caches at fault time. Note that all the
- dma_buf files share the same anon inode, hence the exporter needs to replace
- the dma_buf file stored in vma->vm_file with it's own if pte shootdown is
- required. This is because the kernel uses the underlying inode's address_space
- for vma tracking (and hence pte tracking at shootdown time with
- unmap_mapping_range).
-
- If the above shootdown dance turns out to be too expensive in certain
- scenarios, we can extend dma-buf with a more explicit cache tracking scheme
- for userspace mappings. But the current assumption is that using mmap is
- always a slower path, so some inefficiencies should be acceptable.
-
- Exporters that shoot down mappings (for any reasons) shall not do any
- synchronization at fault time with outstanding device operations.
- Synchronization is an orthogonal issue to sharing the backing storage of a
- buffer and hence should not be handled by dma-buf itself. This is explicitly
- mentioned here because many people seem to want something like this, but if
- different exporters handle this differently, buffer sharing can fail in
- interesting ways depending upong the exporter (if userspace starts depending
- upon this implicit synchronization).
-
-Other Interfaces Exposed to Userspace on the dma-buf FD
-------------------------------------------------------
-
-- Since kernel 3.12 the dma-buf FD supports the llseek system call, but only
- with offset=0 and whence=SEEK_END|SEEK_SET. SEEK_SET is supported to allow
- the usual size discover pattern size = SEEK_END(0); SEEK_SET(0). Every other
- llseek operation will report -EINVAL.
-
- If llseek on dma-buf FDs isn't support the kernel will report -ESPIPE for all
- cases. Userspace can use this to detect support for discovering the dma-buf
- size using llseek.
-
-Miscellaneous notes
--------------------
-
-- Any exporters or users of the dma-buf buffer sharing framework must have
- a 'select DMA_SHARED_BUFFER' in their respective Kconfigs.
-
-- In order to avoid fd leaks on exec, the FD_CLOEXEC flag must be set
- on the file descriptor. This is not just a resource leak, but a
- potential security hole. It could give the newly exec'd application
- access to buffers, via the leaked fd, to which it should otherwise
- not be permitted access.
-
- The problem with doing this via a separate fcntl() call, versus doing it
- atomically when the fd is created, is that this is inherently racy in a
- multi-threaded app[3]. The issue is made worse when it is library code
- opening/creating the file descriptor, as the application may not even be
- aware of the fd's.
-
- To avoid this problem, userspace must have a way to request O_CLOEXEC
- flag be set when the dma-buf fd is created. So any API provided by
- the exporting driver to create a dmabuf fd must provide a way to let
- userspace control setting of O_CLOEXEC flag passed in to dma_buf_fd().
-
-- If an exporter needs to manually flush caches and hence needs to fake
- coherency for mmap support, it needs to be able to zap all the ptes pointing
- at the backing storage. Now linux mm needs a struct address_space associated
- with the struct file stored in vma->vm_file to do that with the function
- unmap_mapping_range. But the dma_buf framework only backs every dma_buf fd
- with the anon_file struct file, i.e. all dma_bufs share the same file.
-
- Hence exporters need to setup their own file (and address_space) association
- by setting vma->vm_file and adjusting vma->vm_pgoff in the dma_buf mmap
- callback. In the specific case of a gem driver the exporter could use the
- shmem file already provided by gem (and set vm_pgoff = 0). Exporters can then
- zap ptes by unmapping the corresponding range of the struct address_space
- associated with their own file.
-
-References:
-[1] struct dma_buf_ops in include/linux/dma-buf.h
-[2] All interfaces mentioned above defined in include/linux/dma-buf.h
-[3] https://lwn.net/Articles/236486/
diff --git a/Documentation/dma/DMA-API-HOWTO.txt b/Documentation/dma/DMA-API-HOWTO.txt
new file mode 100644
index 0000000..5e98303
--- /dev/null
+++ b/Documentation/dma/DMA-API-HOWTO.txt
@@ -0,0 +1,915 @@
+ Dynamic DMA mapping Guide
+ =========================
+
+ David S. Miller <davem@xxxxxxxxxx>
+ Richard Henderson <rth@xxxxxxxxxx>
+ Jakub Jelinek <jakub@xxxxxxxxxx>
+
+This is a guide to device driver writers on how to use the DMA API
+with example pseudo-code. For a concise description of the API, see
+DMA-API.txt.
+
+Most of the 64bit platforms have special hardware that translates bus
+addresses (DMA addresses) into physical addresses. This is similar to
+how page tables and/or a TLB translates virtual addresses to physical
+addresses on a CPU. This is needed so that e.g. PCI devices can
+access with a Single Address Cycle (32bit DMA address) any page in the
+64bit physical address space. Previously in Linux those 64bit
+platforms had to set artificial limits on the maximum RAM size in the
+system, so that the virt_to_bus() static scheme works (the DMA address
+translation tables were simply filled on bootup to map each bus
+address to the physical page __pa(bus_to_virt())).
+
+So that Linux can use the dynamic DMA mapping, it needs some help from the
+drivers, namely it has to take into account that DMA addresses should be
+mapped only for the time they are actually used and unmapped after the DMA
+transfer.
+
+The following API will work of course even on platforms where no such
+hardware exists.
+
+Note that the DMA API works with any bus independent of the underlying
+microprocessor architecture. You should use the DMA API rather than
+the bus specific DMA API (e.g. pci_dma_*).
+
+First of all, you should make sure
+
+#include <linux/dma-mapping.h>
+
+is in your driver. This file will obtain for you the definition of the
+dma_addr_t (which can hold any valid DMA address for the platform)
+type which should be used everywhere you hold a DMA (bus) address
+returned from the DMA mapping functions.
+
+ What memory is DMA'able?
+
+The first piece of information you must know is what kernel memory can
+be used with the DMA mapping facilities. There has been an unwritten
+set of rules regarding this, and this text is an attempt to finally
+write them down.
+
+If you acquired your memory via the page allocator
+(i.e. __get_free_page*()) or the generic memory allocators
+(i.e. kmalloc() or kmem_cache_alloc()) then you may DMA to/from
+that memory using the addresses returned from those routines.
+
+This means specifically that you may _not_ use the memory/addresses
+returned from vmalloc() for DMA. It is possible to DMA to the
+_underlying_ memory mapped into a vmalloc() area, but this requires
+walking page tables to get the physical addresses, and then
+translating each of those pages back to a kernel address using
+something like __va(). [ EDIT: Update this when we integrate
+Gerd Knorr's generic code which does this. ]
+
+This rule also means that you may use neither kernel image addresses
+(items in data/text/bss segments), nor module image addresses, nor
+stack addresses for DMA. These could all be mapped somewhere entirely
+different than the rest of physical memory. Even if those classes of
+memory could physically work with DMA, you'd need to ensure the I/O
+buffers were cacheline-aligned. Without that, you'd see cacheline
+sharing problems (data corruption) on CPUs with DMA-incoherent caches.
+(The CPU could write to one word, DMA would write to a different one
+in the same cache line, and one of them could be overwritten.)
+
+Also, this means that you cannot take the return of a kmap()
+call and DMA to/from that. This is similar to vmalloc().
+
+What about block I/O and networking buffers? The block I/O and
+networking subsystems make sure that the buffers they use are valid
+for you to DMA from/to.
+
+ DMA addressing limitations
+
+Does your device have any DMA addressing limitations? For example, is
+your device only capable of driving the low order 24-bits of address?
+If so, you need to inform the kernel of this fact.
+
+By default, the kernel assumes that your device can address the full
+32-bits. For a 64-bit capable device, this needs to be increased.
+And for a device with limitations, as discussed in the previous
+paragraph, it needs to be decreased.
+
+Special note about PCI: PCI-X specification requires PCI-X devices to
+support 64-bit addressing (DAC) for all transactions. And at least
+one platform (SGI SN2) requires 64-bit consistent allocations to
+operate correctly when the IO bus is in PCI-X mode.
+
+For correct operation, you must interrogate the kernel in your device
+probe routine to see if the DMA controller on the machine can properly
+support the DMA addressing limitation your device has. It is good
+style to do this even if your device holds the default setting,
+because this shows that you did think about these issues wrt. your
+device.
+
+The query is performed via a call to dma_set_mask_and_coherent():
+
+ int dma_set_mask_and_coherent(struct device *dev, u64 mask);
+
+which will query the mask for both streaming and coherent APIs together.
+If you have some special requirements, then the following two separate
+queries can be used instead:
+
+ The query for streaming mappings is performed via a call to
+ dma_set_mask():
+
+ int dma_set_mask(struct device *dev, u64 mask);
+
+ The query for consistent allocations is performed via a call
+ to dma_set_coherent_mask():
+
+ int dma_set_coherent_mask(struct device *dev, u64 mask);
+
+Here, dev is a pointer to the device struct of your device, and mask
+is a bit mask describing which bits of an address your device
+supports. It returns zero if your card can perform DMA properly on
+the machine given the address mask you provided. In general, the
+device struct of your device is embedded in the bus specific device
+struct of your device. For example, a pointer to the device struct of
+your PCI device is pdev->dev (pdev is a pointer to the PCI device
+struct of your device).
+
+If it returns non-zero, your device cannot perform DMA properly on
+this platform, and attempting to do so will result in undefined
+behavior. You must either use a different mask, or not use DMA.
+
+This means that in the failure case, you have three options:
+
+1) Use another DMA mask, if possible (see below).
+2) Use some non-DMA mode for data transfer, if possible.
+3) Ignore this device and do not initialize it.
+
+It is recommended that your driver print a kernel KERN_WARNING message
+when you end up performing either #2 or #3. In this manner, if a user
+of your driver reports that performance is bad or that the device is not
+even detected, you can ask them for the kernel messages to find out
+exactly why.
+
+The standard 32-bit addressing device would do something like this:
+
+ if (dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32))) {
+ printk(KERN_WARNING
+ "mydev: No suitable DMA available.\n");
+ goto ignore_this_device;
+ }
+
+Another common scenario is a 64-bit capable device. The approach here
+is to try for 64-bit addressing, but back down to a 32-bit mask that
+should not fail. The kernel may fail the 64-bit mask not because the
+platform is not capable of 64-bit addressing. Rather, it may fail in
+this case simply because 32-bit addressing is done more efficiently
+than 64-bit addressing. For example, Sparc64 PCI SAC addressing is
+more efficient than DAC addressing.
+
+Here is how you would handle a 64-bit capable device which can drive
+all 64-bits when accessing streaming DMA:
+
+ int using_dac;
+
+ if (!dma_set_mask(dev, DMA_BIT_MASK(64))) {
+ using_dac = 1;
+ } else if (!dma_set_mask(dev, DMA_BIT_MASK(32))) {
+ using_dac = 0;
+ } else {
+ printk(KERN_WARNING
+ "mydev: No suitable DMA available.\n");
+ goto ignore_this_device;
+ }
+
+If a card is capable of using 64-bit consistent allocations as well,
+the case would look like this:
+
+ int using_dac, consistent_using_dac;
+
+ if (!dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64))) {
+ using_dac = 1;
+ consistent_using_dac = 1;
+ } else if (!dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32))) {
+ using_dac = 0;
+ consistent_using_dac = 0;
+ } else {
+ printk(KERN_WARNING
+ "mydev: No suitable DMA available.\n");
+ goto ignore_this_device;
+ }
+
+The coherent coherent mask will always be able to set the same or a
+smaller mask as the streaming mask. However for the rare case that a
+device driver only uses consistent allocations, one would have to
+check the return value from dma_set_coherent_mask().
+
+Finally, if your device can only drive the low 24-bits of
+address you might do something like:
+
+ if (dma_set_mask(dev, DMA_BIT_MASK(24))) {
+ printk(KERN_WARNING
+ "mydev: 24-bit DMA addressing not available.\n");
+ goto ignore_this_device;
+ }
+
+When dma_set_mask() or dma_set_mask_and_coherent() is successful, and
+returns zero, the kernel saves away this mask you have provided. The
+kernel will use this information later when you make DMA mappings.
+
+There is a case which we are aware of at this time, which is worth
+mentioning in this documentation. If your device supports multiple
+functions (for example a sound card provides playback and record
+functions) and the various different functions have _different_
+DMA addressing limitations, you may wish to probe each mask and
+only provide the functionality which the machine can handle. It
+is important that the last call to dma_set_mask() be for the
+most specific mask.
+
+Here is pseudo-code showing how this might be done:
+
+ #define PLAYBACK_ADDRESS_BITS DMA_BIT_MASK(32)
+ #define RECORD_ADDRESS_BITS DMA_BIT_MASK(24)
+
+ struct my_sound_card *card;
+ struct device *dev;
+
+ ...
+ if (!dma_set_mask(dev, PLAYBACK_ADDRESS_BITS)) {
+ card->playback_enabled = 1;
+ } else {
+ card->playback_enabled = 0;
+ printk(KERN_WARNING "%s: Playback disabled due to DMA limitations.\n",
+ card->name);
+ }
+ if (!dma_set_mask(dev, RECORD_ADDRESS_BITS)) {
+ card->record_enabled = 1;
+ } else {
+ card->record_enabled = 0;
+ printk(KERN_WARNING "%s: Record disabled due to DMA limitations.\n",
+ card->name);
+ }
+
+A sound card was used as an example here because this genre of PCI
+devices seems to be littered with ISA chips given a PCI front end,
+and thus retaining the 16MB DMA addressing limitations of ISA.
+
+ Types of DMA mappings
+
+There are two types of DMA mappings:
+
+- Consistent DMA mappings which are usually mapped at driver
+ initialization, unmapped at the end and for which the hardware should
+ guarantee that the device and the CPU can access the data
+ in parallel and will see updates made by each other without any
+ explicit software flushing.
+
+ Think of "consistent" as "synchronous" or "coherent".
+
+ The current default is to return consistent memory in the low 32
+ bits of the bus space. However, for future compatibility you should
+ set the consistent mask even if this default is fine for your
+ driver.
+
+ Good examples of what to use consistent mappings for are:
+
+ - Network card DMA ring descriptors.
+ - SCSI adapter mailbox command data structures.
+ - Device firmware microcode executed out of
+ main memory.
+
+ The invariant these examples all require is that any CPU store
+ to memory is immediately visible to the device, and vice
+ versa. Consistent mappings guarantee this.
+
+ IMPORTANT: Consistent DMA memory does not preclude the usage of
+ proper memory barriers. The CPU may reorder stores to
+ consistent memory just as it may normal memory. Example:
+ if it is important for the device to see the first word
+ of a descriptor updated before the second, you must do
+ something like:
+
+ desc->word0 = address;
+ wmb();
+ desc->word1 = DESC_VALID;
+
+ in order to get correct behavior on all platforms.
+
+ Also, on some platforms your driver may need to flush CPU write
+ buffers in much the same way as it needs to flush write buffers
+ found in PCI bridges (such as by reading a register's value
+ after writing it).
+
+- Streaming DMA mappings which are usually mapped for one DMA
+ transfer, unmapped right after it (unless you use dma_sync_* below)
+ and for which hardware can optimize for sequential accesses.
+
+ This of "streaming" as "asynchronous" or "outside the coherency
+ domain".
+
+ Good examples of what to use streaming mappings for are:
+
+ - Networking buffers transmitted/received by a device.
+ - Filesystem buffers written/read by a SCSI device.
+
+ The interfaces for using this type of mapping were designed in
+ such a way that an implementation can make whatever performance
+ optimizations the hardware allows. To this end, when using
+ such mappings you must be explicit about what you want to happen.
+
+Neither type of DMA mapping has alignment restrictions that come from
+the underlying bus, although some devices may have such restrictions.
+Also, systems with caches that aren't DMA-coherent will work better
+when the underlying buffers don't share cache lines with other data.
+
+
+ Using Consistent DMA mappings.
+
+To allocate and map large (PAGE_SIZE or so) consistent DMA regions,
+you should do:
+
+ dma_addr_t dma_handle;
+
+ cpu_addr = dma_alloc_coherent(dev, size, &dma_handle, gfp);
+
+where device is a struct device *. This may be called in interrupt
+context with the GFP_ATOMIC flag.
+
+Size is the length of the region you want to allocate, in bytes.
+
+This routine will allocate RAM for that region, so it acts similarly to
+__get_free_pages (but takes size instead of a page order). If your
+driver needs regions sized smaller than a page, you may prefer using
+the dma_pool interface, described below.
+
+The consistent DMA mapping interfaces, for non-NULL dev, will by
+default return a DMA address which is 32-bit addressable. Even if the
+device indicates (via DMA mask) that it may address the upper 32-bits,
+consistent allocation will only return > 32-bit addresses for DMA if
+the consistent DMA mask has been explicitly changed via
+dma_set_coherent_mask(). This is true of the dma_pool interface as
+well.
+
+dma_alloc_coherent returns two values: the virtual address which you
+can use to access it from the CPU and dma_handle which you pass to the
+card.
+
+The cpu return address and the DMA bus master address are both
+guaranteed to be aligned to the smallest PAGE_SIZE order which
+is greater than or equal to the requested size. This invariant
+exists (for example) to guarantee that if you allocate a chunk
+which is smaller than or equal to 64 kilobytes, the extent of the
+buffer you receive will not cross a 64K boundary.
+
+To unmap and free such a DMA region, you call:
+
+ dma_free_coherent(dev, size, cpu_addr, dma_handle);
+
+where dev, size are the same as in the above call and cpu_addr and
+dma_handle are the values dma_alloc_coherent returned to you.
+This function may not be called in interrupt context.
+
+If your driver needs lots of smaller memory regions, you can write
+custom code to subdivide pages returned by dma_alloc_coherent,
+or you can use the dma_pool API to do that. A dma_pool is like
+a kmem_cache, but it uses dma_alloc_coherent not __get_free_pages.
+Also, it understands common hardware constraints for alignment,
+like queue heads needing to be aligned on N byte boundaries.
+
+Create a dma_pool like this:
+
+ struct dma_pool *pool;
+
+ pool = dma_pool_create(name, dev, size, align, alloc);
+
+The "name" is for diagnostics (like a kmem_cache name); dev and size
+are as above. The device's hardware alignment requirement for this
+type of data is "align" (which is expressed in bytes, and must be a
+power of two). If your device has no boundary crossing restrictions,
+pass 0 for alloc; passing 4096 says memory allocated from this pool
+must not cross 4KByte boundaries (but at that time it may be better to
+go for dma_alloc_coherent directly instead).
+
+Allocate memory from a dma pool like this:
+
+ cpu_addr = dma_pool_alloc(pool, flags, &dma_handle);
+
+flags are SLAB_KERNEL if blocking is permitted (not in_interrupt nor
+holding SMP locks), SLAB_ATOMIC otherwise. Like dma_alloc_coherent,
+this returns two values, cpu_addr and dma_handle.
+
+Free memory that was allocated from a dma_pool like this:
+
+ dma_pool_free(pool, cpu_addr, dma_handle);
+
+where pool is what you passed to dma_pool_alloc, and cpu_addr and
+dma_handle are the values dma_pool_alloc returned. This function
+may be called in interrupt context.
+
+Destroy a dma_pool by calling:
+
+ dma_pool_destroy(pool);
+
+Make sure you've called dma_pool_free for all memory allocated
+from a pool before you destroy the pool. This function may not
+be called in interrupt context.
+
+ DMA Direction
+
+The interfaces described in subsequent portions of this document
+take a DMA direction argument, which is an integer and takes on
+one of the following values:
+
+ DMA_BIDIRECTIONAL
+ DMA_TO_DEVICE
+ DMA_FROM_DEVICE
+ DMA_NONE
+
+One should provide the exact DMA direction if you know it.
+
+DMA_TO_DEVICE means "from main memory to the device"
+DMA_FROM_DEVICE means "from the device to main memory"
+It is the direction in which the data moves during the DMA
+transfer.
+
+You are _strongly_ encouraged to specify this as precisely
+as you possibly can.
+
+If you absolutely cannot know the direction of the DMA transfer,
+specify DMA_BIDIRECTIONAL. It means that the DMA can go in
+either direction. The platform guarantees that you may legally
+specify this, and that it will work, but this may be at the
+cost of performance for example.
+
+The value DMA_NONE is to be used for debugging. One can
+hold this in a data structure before you come to know the
+precise direction, and this will help catch cases where your
+direction tracking logic has failed to set things up properly.
+
+Another advantage of specifying this value precisely (outside of
+potential platform-specific optimizations of such) is for debugging.
+Some platforms actually have a write permission boolean which DMA
+mappings can be marked with, much like page protections in the user
+program address space. Such platforms can and do report errors in the
+kernel logs when the DMA controller hardware detects violation of the
+permission setting.
+
+Only streaming mappings specify a direction, consistent mappings
+implicitly have a direction attribute setting of
+DMA_BIDIRECTIONAL.
+
+The SCSI subsystem tells you the direction to use in the
+'sc_data_direction' member of the SCSI command your driver is
+working on.
+
+For Networking drivers, it's a rather simple affair. For transmit
+packets, map/unmap them with the DMA_TO_DEVICE direction
+specifier. For receive packets, just the opposite, map/unmap them
+with the DMA_FROM_DEVICE direction specifier.
+
+ Using Streaming DMA mappings
+
+The streaming DMA mapping routines can be called from interrupt
+context. There are two versions of each map/unmap, one which will
+map/unmap a single memory region, and one which will map/unmap a
+scatterlist.
+
+To map a single region, you do:
+
+ struct device *dev = &my_dev->dev;
+ dma_addr_t dma_handle;
+ void *addr = buffer->ptr;
+ size_t size = buffer->len;
+
+ dma_handle = dma_map_single(dev, addr, size, direction);
+ if (dma_mapping_error(dma_handle)) {
+ /*
+ * reduce current DMA mapping usage,
+ * delay and try again later or
+ * reset driver.
+ */
+ goto map_error_handling;
+ }
+
+and to unmap it:
+
+ dma_unmap_single(dev, dma_handle, size, direction);
+
+You should call dma_mapping_error() as dma_map_single() could fail and return
+error. Not all dma implementations support dma_mapping_error() interface.
+However, it is a good practice to call dma_mapping_error() interface, which
+will invoke the generic mapping error check interface. Doing so will ensure
+that the mapping code will work correctly on all dma implementations without
+any dependency on the specifics of the underlying implementation. Using the
+returned address without checking for errors could result in failures ranging
+from panics to silent data corruption. A couple of examples of incorrect ways
+to check for errors that make assumptions about the underlying dma
+implementation are as follows and these are applicable to dma_map_page() as
+well.
+
+Incorrect example 1:
+ dma_addr_t dma_handle;
+
+ dma_handle = dma_map_single(dev, addr, size, direction);
+ if ((dma_handle & 0xffff != 0) || (dma_handle >= 0x1000000)) {
+ goto map_error;
+ }
+
+Incorrect example 2:
+ dma_addr_t dma_handle;
+
+ dma_handle = dma_map_single(dev, addr, size, direction);
+ if (dma_handle == DMA_ERROR_CODE) {
+ goto map_error;
+ }
+
+You should call dma_unmap_single when the DMA activity is finished, e.g.
+from the interrupt which told you that the DMA transfer is done.
+
+Using cpu pointers like this for single mappings has a disadvantage,
+you cannot reference HIGHMEM memory in this way. Thus, there is a
+map/unmap interface pair akin to dma_{map,unmap}_single. These
+interfaces deal with page/offset pairs instead of cpu pointers.
+Specifically:
+
+ struct device *dev = &my_dev->dev;
+ dma_addr_t dma_handle;
+ struct page *page = buffer->page;
+ unsigned long offset = buffer->offset;
+ size_t size = buffer->len;
+
+ dma_handle = dma_map_page(dev, page, offset, size, direction);
+ if (dma_mapping_error(dma_handle)) {
+ /*
+ * reduce current DMA mapping usage,
+ * delay and try again later or
+ * reset driver.
+ */
+ goto map_error_handling;
+ }
+
+ ...
+
+ dma_unmap_page(dev, dma_handle, size, direction);
+
+Here, "offset" means byte offset within the given page.
+
+You should call dma_mapping_error() as dma_map_page() could fail and return
+error as outlined under the dma_map_single() discussion.
+
+You should call dma_unmap_page when the DMA activity is finished, e.g.
+from the interrupt which told you that the DMA transfer is done.
+
+With scatterlists, you map a region gathered from several regions by:
+
+ int i, count = dma_map_sg(dev, sglist, nents, direction);
+ struct scatterlist *sg;
+
+ for_each_sg(sglist, sg, count, i) {
+ hw_address[i] = sg_dma_address(sg);
+ hw_len[i] = sg_dma_len(sg);
+ }
+
+where nents is the number of entries in the sglist.
+
+The implementation is free to merge several consecutive sglist entries
+into one (e.g. if DMA mapping is done with PAGE_SIZE granularity, any
+consecutive sglist entries can be merged into one provided the first one
+ends and the second one starts on a page boundary - in fact this is a huge
+advantage for cards which either cannot do scatter-gather or have very
+limited number of scatter-gather entries) and returns the actual number
+of sg entries it mapped them to. On failure 0 is returned.
+
+Then you should loop count times (note: this can be less than nents times)
+and use sg_dma_address() and sg_dma_len() macros where you previously
+accessed sg->address and sg->length as shown above.
+
+To unmap a scatterlist, just call:
+
+ dma_unmap_sg(dev, sglist, nents, direction);
+
+Again, make sure DMA activity has already finished.
+
+PLEASE NOTE: The 'nents' argument to the dma_unmap_sg call must be
+ the _same_ one you passed into the dma_map_sg call,
+ it should _NOT_ be the 'count' value _returned_ from the
+ dma_map_sg call.
+
+Every dma_map_{single,sg} call should have its dma_unmap_{single,sg}
+counterpart, because the bus address space is a shared resource (although
+in some ports the mapping is per each BUS so less devices contend for the
+same bus address space) and you could render the machine unusable by eating
+all bus addresses.
+
+If you need to use the same streaming DMA region multiple times and touch
+the data in between the DMA transfers, the buffer needs to be synced
+properly in order for the cpu and device to see the most uptodate and
+correct copy of the DMA buffer.
+
+So, firstly, just map it with dma_map_{single,sg}, and after each DMA
+transfer call either:
+
+ dma_sync_single_for_cpu(dev, dma_handle, size, direction);
+
+or:
+
+ dma_sync_sg_for_cpu(dev, sglist, nents, direction);
+
+as appropriate.
+
+Then, if you wish to let the device get at the DMA area again,
+finish accessing the data with the cpu, and then before actually
+giving the buffer to the hardware call either:
+
+ dma_sync_single_for_device(dev, dma_handle, size, direction);
+
+or:
+
+ dma_sync_sg_for_device(dev, sglist, nents, direction);
+
+as appropriate.
+
+After the last DMA transfer call one of the DMA unmap routines
+dma_unmap_{single,sg}. If you don't touch the data from the first dma_map_*
+call till dma_unmap_*, then you don't have to call the dma_sync_*
+routines at all.
+
+Here is pseudo code which shows a situation in which you would need
+to use the dma_sync_*() interfaces.
+
+ my_card_setup_receive_buffer(struct my_card *cp, char *buffer, int len)
+ {
+ dma_addr_t mapping;
+
+ mapping = dma_map_single(cp->dev, buffer, len, DMA_FROM_DEVICE);
+ if (dma_mapping_error(dma_handle)) {
+ /*
+ * reduce current DMA mapping usage,
+ * delay and try again later or
+ * reset driver.
+ */
+ goto map_error_handling;
+ }
+
+ cp->rx_buf = buffer;
+ cp->rx_len = len;
+ cp->rx_dma = mapping;
+
+ give_rx_buf_to_card(cp);
+ }
+
+ ...
+
+ my_card_interrupt_handler(int irq, void *devid, struct pt_regs *regs)
+ {
+ struct my_card *cp = devid;
+
+ ...
+ if (read_card_status(cp) == RX_BUF_TRANSFERRED) {
+ struct my_card_header *hp;
+
+ /* Examine the header to see if we wish
+ * to accept the data. But synchronize
+ * the DMA transfer with the CPU first
+ * so that we see updated contents.
+ */
+ dma_sync_single_for_cpu(&cp->dev, cp->rx_dma,
+ cp->rx_len,
+ DMA_FROM_DEVICE);
+
+ /* Now it is safe to examine the buffer. */
+ hp = (struct my_card_header *) cp->rx_buf;
+ if (header_is_ok(hp)) {
+ dma_unmap_single(&cp->dev, cp->rx_dma, cp->rx_len,
+ DMA_FROM_DEVICE);
+ pass_to_upper_layers(cp->rx_buf);
+ make_and_setup_new_rx_buf(cp);
+ } else {
+ /* CPU should not write to
+ * DMA_FROM_DEVICE-mapped area,
+ * so dma_sync_single_for_device() is
+ * not needed here. It would be required
+ * for DMA_BIDIRECTIONAL mapping if
+ * the memory was modified.
+ */
+ give_rx_buf_to_card(cp);
+ }
+ }
+ }
+
+Drivers converted fully to this interface should not use virt_to_bus any
+longer, nor should they use bus_to_virt. Some drivers have to be changed a
+little bit, because there is no longer an equivalent to bus_to_virt in the
+dynamic DMA mapping scheme - you have to always store the DMA addresses
+returned by the dma_alloc_coherent, dma_pool_alloc, and dma_map_single
+calls (dma_map_sg stores them in the scatterlist itself if the platform
+supports dynamic DMA mapping in hardware) in your driver structures and/or
+in the card registers.
+
+All drivers should be using these interfaces with no exceptions. It
+is planned to completely remove virt_to_bus() and bus_to_virt() as
+they are entirely deprecated. Some ports already do not provide these
+as it is impossible to correctly support them.
+
+ Handling Errors
+
+DMA address space is limited on some architectures and an allocation
+failure can be determined by:
+
+- checking if dma_alloc_coherent returns NULL or dma_map_sg returns 0
+
+- checking the returned dma_addr_t of dma_map_single and dma_map_page
+ by using dma_mapping_error():
+
+ dma_addr_t dma_handle;
+
+ dma_handle = dma_map_single(dev, addr, size, direction);
+ if (dma_mapping_error(dev, dma_handle)) {
+ /*
+ * reduce current DMA mapping usage,
+ * delay and try again later or
+ * reset driver.
+ */
+ goto map_error_handling;
+ }
+
+- unmap pages that are already mapped, when mapping error occurs in the middle
+ of a multiple page mapping attempt. These example are applicable to
+ dma_map_page() as well.
+
+Example 1:
+ dma_addr_t dma_handle1;
+ dma_addr_t dma_handle2;
+
+ dma_handle1 = dma_map_single(dev, addr, size, direction);
+ if (dma_mapping_error(dev, dma_handle1)) {
+ /*
+ * reduce current DMA mapping usage,
+ * delay and try again later or
+ * reset driver.
+ */
+ goto map_error_handling1;
+ }
+ dma_handle2 = dma_map_single(dev, addr, size, direction);
+ if (dma_mapping_error(dev, dma_handle2)) {
+ /*
+ * reduce current DMA mapping usage,
+ * delay and try again later or
+ * reset driver.
+ */
+ goto map_error_handling2;
+ }
+
+ ...
+
+ map_error_handling2:
+ dma_unmap_single(dma_handle1);
+ map_error_handling1:
+
+Example 2: (if buffers are allocated in a loop, unmap all mapped buffers when
+ mapping error is detected in the middle)
+
+ dma_addr_t dma_addr;
+ dma_addr_t array[DMA_BUFFERS];
+ int save_index = 0;
+
+ for (i = 0; i < DMA_BUFFERS; i++) {
+
+ ...
+
+ dma_addr = dma_map_single(dev, addr, size, direction);
+ if (dma_mapping_error(dev, dma_addr)) {
+ /*
+ * reduce current DMA mapping usage,
+ * delay and try again later or
+ * reset driver.
+ */
+ goto map_error_handling;
+ }
+ array[i].dma_addr = dma_addr;
+ save_index++;
+ }
+
+ ...
+
+ map_error_handling:
+
+ for (i = 0; i < save_index; i++) {
+
+ ...
+
+ dma_unmap_single(array[i].dma_addr);
+ }
+
+Networking drivers must call dev_kfree_skb to free the socket buffer
+and return NETDEV_TX_OK if the DMA mapping fails on the transmit hook
+(ndo_start_xmit). This means that the socket buffer is just dropped in
+the failure case.
+
+SCSI drivers must return SCSI_MLQUEUE_HOST_BUSY if the DMA mapping
+fails in the queuecommand hook. This means that the SCSI subsystem
+passes the command to the driver again later.
+
+ Optimizing Unmap State Space Consumption
+
+On many platforms, dma_unmap_{single,page}() is simply a nop.
+Therefore, keeping track of the mapping address and length is a waste
+of space. Instead of filling your drivers up with ifdefs and the like
+to "work around" this (which would defeat the whole purpose of a
+portable API) the following facilities are provided.
+
+Actually, instead of describing the macros one by one, we'll
+transform some example code.
+
+1) Use DEFINE_DMA_UNMAP_{ADDR,LEN} in state saving structures.
+ Example, before:
+
+ struct ring_state {
+ struct sk_buff *skb;
+ dma_addr_t mapping;
+ __u32 len;
+ };
+
+ after:
+
+ struct ring_state {
+ struct sk_buff *skb;
+ DEFINE_DMA_UNMAP_ADDR(mapping);
+ DEFINE_DMA_UNMAP_LEN(len);
+ };
+
+2) Use dma_unmap_{addr,len}_set to set these values.
+ Example, before:
+
+ ringp->mapping = FOO;
+ ringp->len = BAR;
+
+ after:
+
+ dma_unmap_addr_set(ringp, mapping, FOO);
+ dma_unmap_len_set(ringp, len, BAR);
+
+3) Use dma_unmap_{addr,len} to access these values.
+ Example, before:
+
+ dma_unmap_single(dev, ringp->mapping, ringp->len,
+ DMA_FROM_DEVICE);
+
+ after:
+
+ dma_unmap_single(dev,
+ dma_unmap_addr(ringp, mapping),
+ dma_unmap_len(ringp, len),
+ DMA_FROM_DEVICE);
+
+It really should be self-explanatory. We treat the ADDR and LEN
+separately, because it is possible for an implementation to only
+need the address in order to perform the unmap operation.
+
+ Platform Issues
+
+If you are just writing drivers for Linux and do not maintain
+an architecture port for the kernel, you can safely skip down
+to "Closing".
+
+1) Struct scatterlist requirements.
+
+ Don't invent the architecture specific struct scatterlist; just use
+ <asm-generic/scatterlist.h>. You need to enable
+ CONFIG_NEED_SG_DMA_LENGTH if the architecture supports IOMMUs
+ (including software IOMMU).
+
+2) ARCH_DMA_MINALIGN
+
+ Architectures must ensure that kmalloc'ed buffer is
+ DMA-safe. Drivers and subsystems depend on it. If an architecture
+ isn't fully DMA-coherent (i.e. hardware doesn't ensure that data in
+ the CPU cache is identical to data in main memory),
+ ARCH_DMA_MINALIGN must be set so that the memory allocator
+ makes sure that kmalloc'ed buffer doesn't share a cache line with
+ the others. See arch/arm/include/asm/cache.h as an example.
+
+ Note that ARCH_DMA_MINALIGN is about DMA memory alignment
+ constraints. You don't need to worry about the architecture data
+ alignment constraints (e.g. the alignment constraints about 64-bit
+ objects).
+
+3) Supporting multiple types of IOMMUs
+
+ If your architecture needs to support multiple types of IOMMUs, you
+ can use include/linux/asm-generic/dma-mapping-common.h. It's a
+ library to support the DMA API with multiple types of IOMMUs. Lots
+ of architectures (x86, powerpc, sh, alpha, ia64, microblaze and
+ sparc) use it. Choose one to see how it can be used. If you need to
+ support multiple types of IOMMUs in a single system, the example of
+ x86 or powerpc helps.
+
+ Closing
+
+This document, and the API itself, would not be in its current
+form without the feedback and suggestions from numerous individuals.
+We would like to specifically mention, in no particular order, the
+following people:
+
+ Russell King <rmk@xxxxxxxxxxxxxxxx>
+ Leo Dagum <dagum@xxxxxxxxxxxxxxxxxxx>
+ Ralf Baechle <ralf@xxxxxxxxxxx>
+ Grant Grundler <grundler@xxxxxxxxxx>
+ Jay Estabrook <Jay.Estabrook@xxxxxxxxxx>
+ Thomas Sailer <sailer@xxxxxxxxxxxxxx>
+ Andrea Arcangeli <andrea@xxxxxxx>
+ Jens Axboe <jens.axboe@xxxxxxxxxx>
+ David Mosberger-Tang <davidm@xxxxxxxxxx>
diff --git a/Documentation/dma/DMA-API.txt b/Documentation/dma/DMA-API.txt
new file mode 100644
index 0000000..e865279
--- /dev/null
+++ b/Documentation/dma/DMA-API.txt
@@ -0,0 +1,700 @@
+ Dynamic DMA mapping using the generic device
+ ============================================
+
+ James E.J. Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
+
+This document describes the DMA API. For a more gentle introduction
+of the API (and actual examples) see
+Documentation/DMA-API-HOWTO.txt.
+
+This API is split into two pieces. Part I describes the API. Part II
+describes the extensions to the API for supporting non-consistent
+memory machines. Unless you know that your driver absolutely has to
+support non-consistent platforms (this is usually only legacy
+platforms) you should only use the API described in part I.
+
+Part I - dma_ API
+-------------------------------------
+
+To get the dma_ API, you must #include <linux/dma-mapping.h>
+
+
+Part Ia - Using large dma-coherent buffers
+------------------------------------------
+
+void *
+dma_alloc_coherent(struct device *dev, size_t size,
+ dma_addr_t *dma_handle, gfp_t flag)
+
+Consistent memory is memory for which a write by either the device or
+the processor can immediately be read by the processor or device
+without having to worry about caching effects. (You may however need
+to make sure to flush the processor's write buffers before telling
+devices to read that memory.)
+
+This routine allocates a region of <size> bytes of consistent memory.
+It also returns a <dma_handle> which may be cast to an unsigned
+integer the same width as the bus and used as the physical address
+base of the region.
+
+Returns: a pointer to the allocated region (in the processor's virtual
+address space) or NULL if the allocation failed.
+
+Note: consistent memory can be expensive on some platforms, and the
+minimum allocation length may be as big as a page, so you should
+consolidate your requests for consistent memory as much as possible.
+The simplest way to do that is to use the dma_pool calls (see below).
+
+The flag parameter (dma_alloc_coherent only) allows the caller to
+specify the GFP_ flags (see kmalloc) for the allocation (the
+implementation may choose to ignore flags that affect the location of
+the returned memory, like GFP_DMA).
+
+void *
+dma_zalloc_coherent(struct device *dev, size_t size,
+ dma_addr_t *dma_handle, gfp_t flag)
+
+Wraps dma_alloc_coherent() and also zeroes the returned memory if the
+allocation attempt succeeded.
+
+void
+dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
+ dma_addr_t dma_handle)
+
+Free the region of consistent memory you previously allocated. dev,
+size and dma_handle must all be the same as those passed into the
+consistent allocate. cpu_addr must be the virtual address returned by
+the consistent allocate.
+
+Note that unlike their sibling allocation calls, these routines
+may only be called with IRQs enabled.
+
+
+Part Ib - Using small dma-coherent buffers
+------------------------------------------
+
+To get this part of the dma_ API, you must #include <linux/dmapool.h>
+
+Many drivers need lots of small dma-coherent memory regions for DMA
+descriptors or I/O buffers. Rather than allocating in units of a page
+or more using dma_alloc_coherent(), you can use DMA pools. These work
+much like a struct kmem_cache, except that they use the dma-coherent allocator,
+not __get_free_pages(). Also, they understand common hardware constraints
+for alignment, like queue heads needing to be aligned on N-byte boundaries.
+
+
+ struct dma_pool *
+ dma_pool_create(const char *name, struct device *dev,
+ size_t size, size_t align, size_t alloc);
+
+The pool create() routines initialize a pool of dma-coherent buffers
+for use with a given device. It must be called in a context which
+can sleep.
+
+The "name" is for diagnostics (like a struct kmem_cache name); dev and size
+are like what you'd pass to dma_alloc_coherent(). The device's hardware
+alignment requirement for this type of data is "align" (which is expressed
+in bytes, and must be a power of two). If your device has no boundary
+crossing restrictions, pass 0 for alloc; passing 4096 says memory allocated
+from this pool must not cross 4KByte boundaries.
+
+
+ void *dma_pool_alloc(struct dma_pool *pool, gfp_t gfp_flags,
+ dma_addr_t *dma_handle);
+
+This allocates memory from the pool; the returned memory will meet the size
+and alignment requirements specified at creation time. Pass GFP_ATOMIC to
+prevent blocking, or if it's permitted (not in_interrupt, not holding SMP locks),
+pass GFP_KERNEL to allow blocking. Like dma_alloc_coherent(), this returns
+two values: an address usable by the cpu, and the dma address usable by the
+pool's device.
+
+
+ void dma_pool_free(struct dma_pool *pool, void *vaddr,
+ dma_addr_t addr);
+
+This puts memory back into the pool. The pool is what was passed to
+the pool allocation routine; the cpu (vaddr) and dma addresses are what
+were returned when that routine allocated the memory being freed.
+
+
+ void dma_pool_destroy(struct dma_pool *pool);
+
+The pool destroy() routines free the resources of the pool. They must be
+called in a context which can sleep. Make sure you've freed all allocated
+memory back to the pool before you destroy it.
+
+
+Part Ic - DMA addressing limitations
+------------------------------------
+
+int
+dma_supported(struct device *dev, u64 mask)
+
+Checks to see if the device can support DMA to the memory described by
+mask.
+
+Returns: 1 if it can and 0 if it can't.
+
+Notes: This routine merely tests to see if the mask is possible. It
+won't change the current mask settings. It is more intended as an
+internal API for use by the platform than an external API for use by
+driver writers.
+
+int
+dma_set_mask_and_coherent(struct device *dev, u64 mask)
+
+Checks to see if the mask is possible and updates the device
+streaming and coherent DMA mask parameters if it is.
+
+Returns: 0 if successful and a negative error if not.
+
+int
+dma_set_mask(struct device *dev, u64 mask)
+
+Checks to see if the mask is possible and updates the device
+parameters if it is.
+
+Returns: 0 if successful and a negative error if not.
+
+int
+dma_set_coherent_mask(struct device *dev, u64 mask)
+
+Checks to see if the mask is possible and updates the device
+parameters if it is.
+
+Returns: 0 if successful and a negative error if not.
+
+u64
+dma_get_required_mask(struct device *dev)
+
+This API returns the mask that the platform requires to
+operate efficiently. Usually this means the returned mask
+is the minimum required to cover all of memory. Examining the
+required mask gives drivers with variable descriptor sizes the
+opportunity to use smaller descriptors as necessary.
+
+Requesting the required mask does not alter the current mask. If you
+wish to take advantage of it, you should issue a dma_set_mask()
+call to set the mask to the value returned.
+
+
+Part Id - Streaming DMA mappings
+--------------------------------
+
+dma_addr_t
+dma_map_single(struct device *dev, void *cpu_addr, size_t size,
+ enum dma_data_direction direction)
+
+Maps a piece of processor virtual memory so it can be accessed by the
+device and returns the physical handle of the memory.
+
+The direction for both api's may be converted freely by casting.
+However the dma_ API uses a strongly typed enumerator for its
+direction:
+
+DMA_NONE no direction (used for debugging)
+DMA_TO_DEVICE data is going from the memory to the device
+DMA_FROM_DEVICE data is coming from the device to the memory
+DMA_BIDIRECTIONAL direction isn't known
+
+Notes: Not all memory regions in a machine can be mapped by this
+API. Further, regions that appear to be physically contiguous in
+kernel virtual space may not be contiguous as physical memory. Since
+this API does not provide any scatter/gather capability, it will fail
+if the user tries to map a non-physically contiguous piece of memory.
+For this reason, it is recommended that memory mapped by this API be
+obtained only from sources which guarantee it to be physically contiguous
+(like kmalloc).
+
+Further, the physical address of the memory must be within the
+dma_mask of the device (the dma_mask represents a bit mask of the
+addressable region for the device. I.e., if the physical address of
+the memory anded with the dma_mask is still equal to the physical
+address, then the device can perform DMA to the memory). In order to
+ensure that the memory allocated by kmalloc is within the dma_mask,
+the driver may specify various platform-dependent flags to restrict
+the physical memory range of the allocation (e.g. on x86, GFP_DMA
+guarantees to be within the first 16Mb of available physical memory,
+as required by ISA devices).
+
+Note also that the above constraints on physical contiguity and
+dma_mask may not apply if the platform has an IOMMU (a device which
+supplies a physical to virtual mapping between the I/O memory bus and
+the device). However, to be portable, device driver writers may *not*
+assume that such an IOMMU exists.
+
+Warnings: Memory coherency operates at a granularity called the cache
+line width. In order for memory mapped by this API to operate
+correctly, the mapped region must begin exactly on a cache line
+boundary and end exactly on one (to prevent two separately mapped
+regions from sharing a single cache line). Since the cache line size
+may not be known at compile time, the API will not enforce this
+requirement. Therefore, it is recommended that driver writers who
+don't take special care to determine the cache line size at run time
+only map virtual regions that begin and end on page boundaries (which
+are guaranteed also to be cache line boundaries).
+
+DMA_TO_DEVICE synchronisation must be done after the last modification
+of the memory region by the software and before it is handed off to
+the driver. Once this primitive is used, memory covered by this
+primitive should be treated as read-only by the device. If the device
+may write to it at any point, it should be DMA_BIDIRECTIONAL (see
+below).
+
+DMA_FROM_DEVICE synchronisation must be done before the driver
+accesses data that may be changed by the device. This memory should
+be treated as read-only by the driver. If the driver needs to write
+to it at any point, it should be DMA_BIDIRECTIONAL (see below).
+
+DMA_BIDIRECTIONAL requires special handling: it means that the driver
+isn't sure if the memory was modified before being handed off to the
+device and also isn't sure if the device will also modify it. Thus,
+you must always sync bidirectional memory twice: once before the
+memory is handed off to the device (to make sure all memory changes
+are flushed from the processor) and once before the data may be
+accessed after being used by the device (to make sure any processor
+cache lines are updated with data that the device may have changed).
+
+void
+dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
+ enum dma_data_direction direction)
+
+Unmaps the region previously mapped. All the parameters passed in
+must be identical to those passed in (and returned) by the mapping
+API.
+
+dma_addr_t
+dma_map_page(struct device *dev, struct page *page,
+ unsigned long offset, size_t size,
+ enum dma_data_direction direction)
+void
+dma_unmap_page(struct device *dev, dma_addr_t dma_address, size_t size,
+ enum dma_data_direction direction)
+
+API for mapping and unmapping for pages. All the notes and warnings
+for the other mapping APIs apply here. Also, although the <offset>
+and <size> parameters are provided to do partial page mapping, it is
+recommended that you never use these unless you really know what the
+cache width is.
+
+int
+dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
+
+In some circumstances dma_map_single and dma_map_page will fail to create
+a mapping. A driver can check for these errors by testing the returned
+dma address with dma_mapping_error(). A non-zero return value means the mapping
+could not be created and the driver should take appropriate action (e.g.
+reduce current DMA mapping usage or delay and try again later).
+
+ int
+ dma_map_sg(struct device *dev, struct scatterlist *sg,
+ int nents, enum dma_data_direction direction)
+
+Returns: the number of physical segments mapped (this may be shorter
+than <nents> passed in if some elements of the scatter/gather list are
+physically or virtually adjacent and an IOMMU maps them with a single
+entry).
+
+Please note that the sg cannot be mapped again if it has been mapped once.
+The mapping process is allowed to destroy information in the sg.
+
+As with the other mapping interfaces, dma_map_sg can fail. When it
+does, 0 is returned and a driver must take appropriate action. It is
+critical that the driver do something, in the case of a block driver
+aborting the request or even oopsing is better than doing nothing and
+corrupting the filesystem.
+
+With scatterlists, you use the resulting mapping like this:
+
+ int i, count = dma_map_sg(dev, sglist, nents, direction);
+ struct scatterlist *sg;
+
+ for_each_sg(sglist, sg, count, i) {
+ hw_address[i] = sg_dma_address(sg);
+ hw_len[i] = sg_dma_len(sg);
+ }
+
+where nents is the number of entries in the sglist.
+
+The implementation is free to merge several consecutive sglist entries
+into one (e.g. with an IOMMU, or if several pages just happen to be
+physically contiguous) and returns the actual number of sg entries it
+mapped them to. On failure 0, is returned.
+
+Then you should loop count times (note: this can be less than nents times)
+and use sg_dma_address() and sg_dma_len() macros where you previously
+accessed sg->address and sg->length as shown above.
+
+ void
+ dma_unmap_sg(struct device *dev, struct scatterlist *sg,
+ int nhwentries, enum dma_data_direction direction)
+
+Unmap the previously mapped scatter/gather list. All the parameters
+must be the same as those and passed in to the scatter/gather mapping
+API.
+
+Note: <nents> must be the number you passed in, *not* the number of
+physical entries returned.
+
+void
+dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
+ enum dma_data_direction direction)
+void
+dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, size_t size,
+ enum dma_data_direction direction)
+void
+dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems,
+ enum dma_data_direction direction)
+void
+dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nelems,
+ enum dma_data_direction direction)
+
+Synchronise a single contiguous or scatter/gather mapping for the cpu
+and device. With the sync_sg API, all the parameters must be the same
+as those passed into the single mapping API. With the sync_single API,
+you can use dma_handle and size parameters that aren't identical to
+those passed into the single mapping API to do a partial sync.
+
+Notes: You must do this:
+
+- Before reading values that have been written by DMA from the device
+ (use the DMA_FROM_DEVICE direction)
+- After writing values that will be written to the device using DMA
+ (use the DMA_TO_DEVICE) direction
+- before *and* after handing memory to the device if the memory is
+ DMA_BIDIRECTIONAL
+
+See also dma_map_single().
+
+dma_addr_t
+dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size,
+ enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+
+void
+dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr,
+ size_t size, enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+
+int
+dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
+ int nents, enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+
+void
+dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl,
+ int nents, enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+
+The four functions above are just like the counterpart functions
+without the _attrs suffixes, except that they pass an optional
+struct dma_attrs*.
+
+struct dma_attrs encapsulates a set of "dma attributes". For the
+definition of struct dma_attrs see linux/dma-attrs.h.
+
+The interpretation of dma attributes is architecture-specific, and
+each attribute should be documented in Documentation/DMA-attributes.txt.
+
+If struct dma_attrs* is NULL, the semantics of each of these
+functions is identical to those of the corresponding function
+without the _attrs suffix. As a result dma_map_single_attrs()
+can generally replace dma_map_single(), etc.
+
+As an example of the use of the *_attrs functions, here's how
+you could pass an attribute DMA_ATTR_FOO when mapping memory
+for DMA:
+
+#include <linux/dma-attrs.h>
+/* DMA_ATTR_FOO should be defined in linux/dma-attrs.h and
+ * documented in Documentation/DMA-attributes.txt */
+...
+
+ DEFINE_DMA_ATTRS(attrs);
+ dma_set_attr(DMA_ATTR_FOO, &attrs);
+ ....
+ n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, &attr);
+ ....
+
+Architectures that care about DMA_ATTR_FOO would check for its
+presence in their implementations of the mapping and unmapping
+routines, e.g.:
+
+void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr,
+ size_t size, enum dma_data_direction dir,
+ struct dma_attrs *attrs)
+{
+ ....
+ int foo = dma_get_attr(DMA_ATTR_FOO, attrs);
+ ....
+ if (foo)
+ /* twizzle the frobnozzle */
+ ....
+
+
+Part II - Advanced dma_ usage
+-----------------------------
+
+Warning: These pieces of the DMA API should not be used in the
+majority of cases, since they cater for unlikely corner cases that
+don't belong in usual drivers.
+
+If you don't understand how cache line coherency works between a
+processor and an I/O device, you should not be using this part of the
+API at all.
+
+void *
+dma_alloc_noncoherent(struct device *dev, size_t size,
+ dma_addr_t *dma_handle, gfp_t flag)
+
+Identical to dma_alloc_coherent() except that the platform will
+choose to return either consistent or non-consistent memory as it sees
+fit. By using this API, you are guaranteeing to the platform that you
+have all the correct and necessary sync points for this memory in the
+driver should it choose to return non-consistent memory.
+
+Note: where the platform can return consistent memory, it will
+guarantee that the sync points become nops.
+
+Warning: Handling non-consistent memory is a real pain. You should
+only ever use this API if you positively know your driver will be
+required to work on one of the rare (usually non-PCI) architectures
+that simply cannot make consistent memory.
+
+void
+dma_free_noncoherent(struct device *dev, size_t size, void *cpu_addr,
+ dma_addr_t dma_handle)
+
+Free memory allocated by the nonconsistent API. All parameters must
+be identical to those passed in (and returned by
+dma_alloc_noncoherent()).
+
+int
+dma_get_cache_alignment(void)
+
+Returns the processor cache alignment. This is the absolute minimum
+alignment *and* width that you must observe when either mapping
+memory or doing partial flushes.
+
+Notes: This API may return a number *larger* than the actual cache
+line, but it will guarantee that one or more cache lines fit exactly
+into the width returned by this call. It will also always be a power
+of two for easy alignment.
+
+void
+dma_cache_sync(struct device *dev, void *vaddr, size_t size,
+ enum dma_data_direction direction)
+
+Do a partial sync of memory that was allocated by
+dma_alloc_noncoherent(), starting at virtual address vaddr and
+continuing on for size. Again, you *must* observe the cache line
+boundaries when doing this.
+
+int
+dma_declare_coherent_memory(struct device *dev, dma_addr_t bus_addr,
+ dma_addr_t device_addr, size_t size, int
+ flags)
+
+Declare region of memory to be handed out by dma_alloc_coherent when
+it's asked for coherent memory for this device.
+
+bus_addr is the physical address to which the memory is currently
+assigned in the bus responding region (this will be used by the
+platform to perform the mapping).
+
+device_addr is the physical address the device needs to be programmed
+with actually to address this memory (this will be handed out as the
+dma_addr_t in dma_alloc_coherent()).
+
+size is the size of the area (must be multiples of PAGE_SIZE).
+
+flags can be or'd together and are:
+
+DMA_MEMORY_MAP - request that the memory returned from
+dma_alloc_coherent() be directly writable.
+
+DMA_MEMORY_IO - request that the memory returned from
+dma_alloc_coherent() be addressable using read/write/memcpy_toio etc.
+
+One or both of these flags must be present.
+
+DMA_MEMORY_INCLUDES_CHILDREN - make the declared memory be allocated by
+dma_alloc_coherent of any child devices of this one (for memory residing
+on a bridge).
+
+DMA_MEMORY_EXCLUSIVE - only allocate memory from the declared regions.
+Do not allow dma_alloc_coherent() to fall back to system memory when
+it's out of memory in the declared region.
+
+The return value will be either DMA_MEMORY_MAP or DMA_MEMORY_IO and
+must correspond to a passed in flag (i.e. no returning DMA_MEMORY_IO
+if only DMA_MEMORY_MAP were passed in) for success or zero for
+failure.
+
+Note, for DMA_MEMORY_IO returns, all subsequent memory returned by
+dma_alloc_coherent() may no longer be accessed directly, but instead
+must be accessed using the correct bus functions. If your driver
+isn't prepared to handle this contingency, it should not specify
+DMA_MEMORY_IO in the input flags.
+
+As a simplification for the platforms, only *one* such region of
+memory may be declared per device.
+
+For reasons of efficiency, most platforms choose to track the declared
+region only at the granularity of a page. For smaller allocations,
+you should use the dma_pool() API.
+
+void
+dma_release_declared_memory(struct device *dev)
+
+Remove the memory region previously declared from the system. This
+API performs *no* in-use checking for this region and will return
+unconditionally having removed all the required structures. It is the
+driver's job to ensure that no parts of this memory region are
+currently in use.
+
+void *
+dma_mark_declared_memory_occupied(struct device *dev,
+ dma_addr_t device_addr, size_t size)
+
+This is used to occupy specific regions of the declared space
+(dma_alloc_coherent() will hand out the first free region it finds).
+
+device_addr is the *device* address of the region requested.
+
+size is the size (and should be a page-sized multiple).
+
+The return value will be either a pointer to the processor virtual
+address of the memory, or an error (via PTR_ERR()) if any part of the
+region is occupied.
+
+Part III - Debug drivers use of the DMA-API
+-------------------------------------------
+
+The DMA-API as described above as some constraints. DMA addresses must be
+released with the corresponding function with the same size for example. With
+the advent of hardware IOMMUs it becomes more and more important that drivers
+do not violate those constraints. In the worst case such a violation can
+result in data corruption up to destroyed filesystems.
+
+To debug drivers and find bugs in the usage of the DMA-API checking code can
+be compiled into the kernel which will tell the developer about those
+violations. If your architecture supports it you can select the "Enable
+debugging of DMA-API usage" option in your kernel configuration. Enabling this
+option has a performance impact. Do not enable it in production kernels.
+
+If you boot the resulting kernel will contain code which does some bookkeeping
+about what DMA memory was allocated for which device. If this code detects an
+error it prints a warning message with some details into your kernel log. An
+example warning message may look like this:
+
+------------[ cut here ]------------
+WARNING: at /data2/repos/linux-2.6-iommu/lib/dma-debug.c:448
+ check_unmap+0x203/0x490()
+Hardware name:
+forcedeth 0000:00:08.0: DMA-API: device driver frees DMA memory with wrong
+ function [device address=0x00000000640444be] [size=66 bytes] [mapped as
+single] [unmapped as page]
+Modules linked in: nfsd exportfs bridge stp llc r8169
+Pid: 0, comm: swapper Tainted: G W 2.6.28-dmatest-09289-g8bb99c0 #1
+Call Trace:
+ <IRQ> [<ffffffff80240b22>] warn_slowpath+0xf2/0x130
+ [<ffffffff80647b70>] _spin_unlock+0x10/0x30
+ [<ffffffff80537e75>] usb_hcd_link_urb_to_ep+0x75/0xc0
+ [<ffffffff80647c22>] _spin_unlock_irqrestore+0x12/0x40
+ [<ffffffff8055347f>] ohci_urb_enqueue+0x19f/0x7c0
+ [<ffffffff80252f96>] queue_work+0x56/0x60
+ [<ffffffff80237e10>] enqueue_task_fair+0x20/0x50
+ [<ffffffff80539279>] usb_hcd_submit_urb+0x379/0xbc0
+ [<ffffffff803b78c3>] cpumask_next_and+0x23/0x40
+ [<ffffffff80235177>] find_busiest_group+0x207/0x8a0
+ [<ffffffff8064784f>] _spin_lock_irqsave+0x1f/0x50
+ [<ffffffff803c7ea3>] check_unmap+0x203/0x490
+ [<ffffffff803c8259>] debug_dma_unmap_page+0x49/0x50
+ [<ffffffff80485f26>] nv_tx_done_optimized+0xc6/0x2c0
+ [<ffffffff80486c13>] nv_nic_irq_optimized+0x73/0x2b0
+ [<ffffffff8026df84>] handle_IRQ_event+0x34/0x70
+ [<ffffffff8026ffe9>] handle_edge_irq+0xc9/0x150
+ [<ffffffff8020e3ab>] do_IRQ+0xcb/0x1c0
+ [<ffffffff8020c093>] ret_from_intr+0x0/0xa
+ <EOI> <4>---[ end trace f6435a98e2a38c0e ]---
+
+The driver developer can find the driver and the device including a stacktrace
+of the DMA-API call which caused this warning.
+
+Per default only the first error will result in a warning message. All other
+errors will only silently counted. This limitation exist to prevent the code
+from flooding your kernel log. To support debugging a device driver this can
+be disabled via debugfs. See the debugfs interface documentation below for
+details.
+
+The debugfs directory for the DMA-API debugging code is called dma-api/. In
+this directory the following files can currently be found:
+
+ dma-api/all_errors This file contains a numeric value. If this
+ value is not equal to zero the debugging code
+ will print a warning for every error it finds
+ into the kernel log. Be careful with this
+ option, as it can easily flood your logs.
+
+ dma-api/disabled This read-only file contains the character 'Y'
+ if the debugging code is disabled. This can
+ happen when it runs out of memory or if it was
+ disabled at boot time
+
+ dma-api/error_count This file is read-only and shows the total
+ numbers of errors found.
+
+ dma-api/num_errors The number in this file shows how many
+ warnings will be printed to the kernel log
+ before it stops. This number is initialized to
+ one at system boot and be set by writing into
+ this file
+
+ dma-api/min_free_entries
+ This read-only file can be read to get the
+ minimum number of free dma_debug_entries the
+ allocator has ever seen. If this value goes
+ down to zero the code will disable itself
+ because it is not longer reliable.
+
+ dma-api/num_free_entries
+ The current number of free dma_debug_entries
+ in the allocator.
+
+ dma-api/driver-filter
+ You can write a name of a driver into this file
+ to limit the debug output to requests from that
+ particular driver. Write an empty string to
+ that file to disable the filter and see
+ all errors again.
+
+If you have this code compiled into your kernel it will be enabled by default.
+If you want to boot without the bookkeeping anyway you can provide
+'dma_debug=off' as a boot parameter. This will disable DMA-API debugging.
+Notice that you can not enable it again at runtime. You have to reboot to do
+so.
+
+If you want to see debug messages only for a special device driver you can
+specify the dma_debug_driver=<drivername> parameter. This will enable the
+driver filter at boot time. The debug code will only print errors for that
+driver afterwards. This filter can be disabled or changed later using debugfs.
+
+When the code disables itself at runtime this is most likely because it ran
+out of dma_debug_entries. These entries are preallocated at boot. The number
+of preallocated entries is defined per architecture. If it is too low for you
+boot with 'dma_debug_entries=<your_desired_number>' to overwrite the
+architectural default.
+
+void debug_dmap_mapping_error(struct device *dev, dma_addr_t dma_addr);
+
+dma-debug interface debug_dma_mapping_error() to debug drivers that fail
+to check dma mapping errors on addresses returned by dma_map_single() and
+dma_map_page() interfaces. This interface clears a flag set by
+debug_dma_map_page() to indicate that dma_mapping_error() has been called by
+the driver. When driver does unmap, debug_dma_unmap() checks the flag and if
+this flag is still set, prints warning message that includes call trace that
+leads up to the unmap. This interface can be called from dma_mapping_error()
+routines to enable dma mapping error check debugging.
+
diff --git a/Documentation/dma/DMA-ISA-LPC.txt b/Documentation/dma/DMA-ISA-LPC.txt
new file mode 100644
index 0000000..e767805
--- /dev/null
+++ b/Documentation/dma/DMA-ISA-LPC.txt
@@ -0,0 +1,151 @@
+ DMA with ISA and LPC devices
+ ============================
+
+ Pierre Ossman <drzeus@xxxxxxxxx>
+
+This document describes how to do DMA transfers using the old ISA DMA
+controller. Even though ISA is more or less dead today the LPC bus
+uses the same DMA system so it will be around for quite some time.
+
+Part I - Headers and dependencies
+---------------------------------
+
+To do ISA style DMA you need to include two headers:
+
+#include <linux/dma-mapping.h>
+#include <asm/dma.h>
+
+The first is the generic DMA API used to convert virtual addresses to
+physical addresses (see Documentation/DMA-API.txt for details).
+
+The second contains the routines specific to ISA DMA transfers. Since
+this is not present on all platforms make sure you construct your
+Kconfig to be dependent on ISA_DMA_API (not ISA) so that nobody tries
+to build your driver on unsupported platforms.
+
+Part II - Buffer allocation
+---------------------------
+
+The ISA DMA controller has some very strict requirements on which
+memory it can access so extra care must be taken when allocating
+buffers.
+
+(You usually need a special buffer for DMA transfers instead of
+transferring directly to and from your normal data structures.)
+
+The DMA-able address space is the lowest 16 MB of _physical_ memory.
+Also the transfer block may not cross page boundaries (which are 64
+or 128 KiB depending on which channel you use).
+
+In order to allocate a piece of memory that satisfies all these
+requirements you pass the flag GFP_DMA to kmalloc.
+
+Unfortunately the memory available for ISA DMA is scarce so unless you
+allocate the memory during boot-up it's a good idea to also pass
+__GFP_REPEAT and __GFP_NOWARN to make the allocater try a bit harder.
+
+(This scarcity also means that you should allocate the buffer as
+early as possible and not release it until the driver is unloaded.)
+
+Part III - Address translation
+------------------------------
+
+To translate the virtual address to a physical use the normal DMA
+API. Do _not_ use isa_virt_to_phys() even though it does the same
+thing. The reason for this is that the function isa_virt_to_phys()
+will require a Kconfig dependency to ISA, not just ISA_DMA_API which
+is really all you need. Remember that even though the DMA controller
+has its origins in ISA it is used elsewhere.
+
+Note: x86_64 had a broken DMA API when it came to ISA but has since
+been fixed. If your arch has problems then fix the DMA API instead of
+reverting to the ISA functions.
+
+Part IV - Channels
+------------------
+
+A normal ISA DMA controller has 8 channels. The lower four are for
+8-bit transfers and the upper four are for 16-bit transfers.
+
+(Actually the DMA controller is really two separate controllers where
+channel 4 is used to give DMA access for the second controller (0-3).
+This means that of the four 16-bits channels only three are usable.)
+
+You allocate these in a similar fashion as all basic resources:
+
+extern int request_dma(unsigned int dmanr, const char * device_id);
+extern void free_dma(unsigned int dmanr);
+
+The ability to use 16-bit or 8-bit transfers is _not_ up to you as a
+driver author but depends on what the hardware supports. Check your
+specs or test different channels.
+
+Part V - Transfer data
+----------------------
+
+Now for the good stuff, the actual DMA transfer. :)
+
+Before you use any ISA DMA routines you need to claim the DMA lock
+using claim_dma_lock(). The reason is that some DMA operations are
+not atomic so only one driver may fiddle with the registers at a
+time.
+
+The first time you use the DMA controller you should call
+clear_dma_ff(). This clears an internal register in the DMA
+controller that is used for the non-atomic operations. As long as you
+(and everyone else) uses the locking functions then you only need to
+reset this once.
+
+Next, you tell the controller in which direction you intend to do the
+transfer using set_dma_mode(). Currently you have the options
+DMA_MODE_READ and DMA_MODE_WRITE.
+
+Set the address from where the transfer should start (this needs to
+be 16-bit aligned for 16-bit transfers) and how many bytes to
+transfer. Note that it's _bytes_. The DMA routines will do all the
+required translation to values that the DMA controller understands.
+
+The final step is enabling the DMA channel and releasing the DMA
+lock.
+
+Once the DMA transfer is finished (or timed out) you should disable
+the channel again. You should also check get_dma_residue() to make
+sure that all data has been transferred.
+
+Example:
+
+int flags, residue;
+
+flags = claim_dma_lock();
+
+clear_dma_ff();
+
+set_dma_mode(channel, DMA_MODE_WRITE);
+set_dma_addr(channel, phys_addr);
+set_dma_count(channel, num_bytes);
+
+dma_enable(channel);
+
+release_dma_lock(flags);
+
+while (!device_done());
+
+flags = claim_dma_lock();
+
+dma_disable(channel);
+
+residue = dma_get_residue(channel);
+if (residue != 0)
+ printk(KERN_ERR "driver: Incomplete DMA transfer!"
+ " %d bytes left!\n", residue);
+
+release_dma_lock(flags);
+
+Part VI - Suspend/resume
+------------------------
+
+It is the driver's responsibility to make sure that the machine isn't
+suspended while a DMA transfer is in progress. Also, all DMA settings
+are lost when the system suspends so if your driver relies on the DMA
+controller being in a certain state then you have to restore these
+registers upon resume.
diff --git a/Documentation/dma/DMA-attributes.txt b/Documentation/dma/DMA-attributes.txt
new file mode 100644
index 0000000..cc2450d
--- /dev/null
+++ b/Documentation/dma/DMA-attributes.txt
@@ -0,0 +1,102 @@
+ DMA attributes
+ ==============
+
+This document describes the semantics of the DMA attributes that are
+defined in linux/dma-attrs.h.
+
+DMA_ATTR_WRITE_BARRIER
+----------------------
+
+DMA_ATTR_WRITE_BARRIER is a (write) barrier attribute for DMA. DMA
+to a memory region with the DMA_ATTR_WRITE_BARRIER attribute forces
+all pending DMA writes to complete, and thus provides a mechanism to
+strictly order DMA from a device across all intervening busses and
+bridges. This barrier is not specific to a particular type of
+interconnect, it applies to the system as a whole, and so its
+implementation must account for the idiosyncrasies of the system all
+the way from the DMA device to memory.
+
+As an example of a situation where DMA_ATTR_WRITE_BARRIER would be
+useful, suppose that a device does a DMA write to indicate that data is
+ready and available in memory. The DMA of the "completion indication"
+could race with data DMA. Mapping the memory used for completion
+indications with DMA_ATTR_WRITE_BARRIER would prevent the race.
+
+DMA_ATTR_WEAK_ORDERING
+----------------------
+
+DMA_ATTR_WEAK_ORDERING specifies that reads and writes to the mapping
+may be weakly ordered, that is that reads and writes may pass each other.
+
+Since it is optional for platforms to implement DMA_ATTR_WEAK_ORDERING,
+those that do not will simply ignore the attribute and exhibit default
+behavior.
+
+DMA_ATTR_WRITE_COMBINE
+----------------------
+
+DMA_ATTR_WRITE_COMBINE specifies that writes to the mapping may be
+buffered to improve performance.
+
+Since it is optional for platforms to implement DMA_ATTR_WRITE_COMBINE,
+those that do not will simply ignore the attribute and exhibit default
+behavior.
+
+DMA_ATTR_NON_CONSISTENT
+-----------------------
+
+DMA_ATTR_NON_CONSISTENT lets the platform to choose to return either
+consistent or non-consistent memory as it sees fit. By using this API,
+you are guaranteeing to the platform that you have all the correct and
+necessary sync points for this memory in the driver.
+
+DMA_ATTR_NO_KERNEL_MAPPING
+--------------------------
+
+DMA_ATTR_NO_KERNEL_MAPPING lets the platform to avoid creating a kernel
+virtual mapping for the allocated buffer. On some architectures creating
+such mapping is non-trivial task and consumes very limited resources
+(like kernel virtual address space or dma consistent address space).
+Buffers allocated with this attribute can be only passed to user space
+by calling dma_mmap_attrs(). By using this API, you are guaranteeing
+that you won't dereference the pointer returned by dma_alloc_attr(). You
+can treat it as a cookie that must be passed to dma_mmap_attrs() and
+dma_free_attrs(). Make sure that both of these also get this attribute
+set on each call.
+
+Since it is optional for platforms to implement
+DMA_ATTR_NO_KERNEL_MAPPING, those that do not will simply ignore the
+attribute and exhibit default behavior.
+
+DMA_ATTR_SKIP_CPU_SYNC
+----------------------
+
+By default dma_map_{single,page,sg} functions family transfer a given
+buffer from CPU domain to device domain. Some advanced use cases might
+require sharing a buffer between more than one device. This requires
+having a mapping created separately for each device and is usually
+performed by calling dma_map_{single,page,sg} function more than once
+for the given buffer with device pointer to each device taking part in
+the buffer sharing. The first call transfers a buffer from 'CPU' domain
+to 'device' domain, what synchronizes CPU caches for the given region
+(usually it means that the cache has been flushed or invalidated
+depending on the dma direction). However, next calls to
+dma_map_{single,page,sg}() for other devices will perform exactly the
+same synchronization operation on the CPU cache. CPU cache synchronization
+might be a time consuming operation, especially if the buffers are
+large, so it is highly recommended to avoid it if possible.
+DMA_ATTR_SKIP_CPU_SYNC allows platform code to skip synchronization of
+the CPU cache for the given buffer assuming that it has been already
+transferred to 'device' domain. This attribute can be also used for
+dma_unmap_{single,page,sg} functions family to force buffer to stay in
+device domain after releasing a mapping for it. Use this attribute with
+care!
+
+DMA_ATTR_FORCE_CONTIGUOUS
+-------------------------
+
+By default DMA-mapping subsystem is allowed to assemble the buffer
+allocated by dma_alloc_attrs() function from individual pages if it can
+be mapped as contiguous chunk into device dma address space. By
+specifing this attribute the allocated buffer is forced to be contiguous
+also in physical memory.
diff --git a/Documentation/dma/dma-buf-sharing.txt b/Documentation/dma/dma-buf-sharing.txt
new file mode 100644
index 0000000..505e711
--- /dev/null
+++ b/Documentation/dma/dma-buf-sharing.txt
@@ -0,0 +1,462 @@
+ DMA Buffer Sharing API Guide
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+ Sumit Semwal
+ <sumit dot semwal at linaro dot org>
+ <sumit dot semwal at ti dot com>
+
+This document serves as a guide to device-driver writers on what is the dma-buf
+buffer sharing API, how to use it for exporting and using shared buffers.
+
+Any device driver which wishes to be a part of DMA buffer sharing, can do so as
+either the 'exporter' of buffers, or the 'user' of buffers.
+
+Say a driver A wants to use buffers created by driver B, then we call B as the
+exporter, and A as buffer-user.
+
+The exporter
+- implements and manages operations[1] for the buffer
+- allows other users to share the buffer by using dma_buf sharing APIs,
+- manages the details of buffer allocation,
+- decides about the actual backing storage where this allocation happens,
+- takes care of any migration of scatterlist - for all (shared) users of this
+ buffer,
+
+The buffer-user
+- is one of (many) sharing users of the buffer.
+- doesn't need to worry about how the buffer is allocated, or where.
+- needs a mechanism to get access to the scatterlist that makes up this buffer
+ in memory, mapped into its own address space, so it can access the same area
+ of memory.
+
+dma-buf operations for device dma only
+--------------------------------------
+
+The dma_buf buffer sharing API usage contains the following steps:
+
+1. Exporter announces that it wishes to export a buffer
+2. Userspace gets the file descriptor associated with the exported buffer, and
+ passes it around to potential buffer-users based on use case
+3. Each buffer-user 'connects' itself to the buffer
+4. When needed, buffer-user requests access to the buffer from exporter
+5. When finished with its use, the buffer-user notifies end-of-DMA to exporter
+6. when buffer-user is done using this buffer completely, it 'disconnects'
+ itself from the buffer.
+
+
+1. Exporter's announcement of buffer export
+
+ The buffer exporter announces its wish to export a buffer. In this, it
+ connects its own private buffer data, provides implementation for operations
+ that can be performed on the exported dma_buf, and flags for the file
+ associated with this buffer.
+
+ Interface:
+ struct dma_buf *dma_buf_export_named(void *priv, struct dma_buf_ops *ops,
+ size_t size, int flags,
+ const char *exp_name)
+
+ If this succeeds, dma_buf_export allocates a dma_buf structure, and returns a
+ pointer to the same. It also associates an anonymous file with this buffer,
+ so it can be exported. On failure to allocate the dma_buf object, it returns
+ NULL.
+
+ 'exp_name' is the name of exporter - to facilitate information while
+ debugging.
+
+ Exporting modules which do not wish to provide any specific name may use the
+ helper define 'dma_buf_export()', with the same arguments as above, but
+ without the last argument; a __FILE__ pre-processor directive will be
+ inserted in place of 'exp_name' instead.
+
+2. Userspace gets a handle to pass around to potential buffer-users
+
+ Userspace entity requests for a file-descriptor (fd) which is a handle to the
+ anonymous file associated with the buffer. It can then share the fd with other
+ drivers and/or processes.
+
+ Interface:
+ int dma_buf_fd(struct dma_buf *dmabuf)
+
+ This API installs an fd for the anonymous file associated with this buffer;
+ returns either 'fd', or error.
+
+3. Each buffer-user 'connects' itself to the buffer
+
+ Each buffer-user now gets a reference to the buffer, using the fd passed to
+ it.
+
+ Interface:
+ struct dma_buf *dma_buf_get(int fd)
+
+ This API will return a reference to the dma_buf, and increment refcount for
+ it.
+
+ After this, the buffer-user needs to attach its device with the buffer, which
+ helps the exporter to know of device buffer constraints.
+
+ Interface:
+ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
+ struct device *dev)
+
+ This API returns reference to an attachment structure, which is then used
+ for scatterlist operations. It will optionally call the 'attach' dma_buf
+ operation, if provided by the exporter.
+
+ The dma-buf sharing framework does the bookkeeping bits related to managing
+ the list of all attachments to a buffer.
+
+Until this stage, the buffer-exporter has the option to choose not to actually
+allocate the backing storage for this buffer, but wait for the first buffer-user
+to request use of buffer for allocation.
+
+
+4. When needed, buffer-user requests access to the buffer
+
+ Whenever a buffer-user wants to use the buffer for any DMA, it asks for
+ access to the buffer using dma_buf_map_attachment API. At least one attach to
+ the buffer must have happened before map_dma_buf can be called.
+
+ Interface:
+ struct sg_table * dma_buf_map_attachment(struct dma_buf_attachment *,
+ enum dma_data_direction);
+
+ This is a wrapper to dma_buf->ops->map_dma_buf operation, which hides the
+ "dma_buf->ops->" indirection from the users of this interface.
+
+ In struct dma_buf_ops, map_dma_buf is defined as
+ struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *,
+ enum dma_data_direction);
+
+ It is one of the buffer operations that must be implemented by the exporter.
+ It should return the sg_table containing scatterlist for this buffer, mapped
+ into caller's address space.
+
+ If this is being called for the first time, the exporter can now choose to
+ scan through the list of attachments for this buffer, collate the requirements
+ of the attached devices, and choose an appropriate backing storage for the
+ buffer.
+
+ Based on enum dma_data_direction, it might be possible to have multiple users
+ accessing at the same time (for reading, maybe), or any other kind of sharing
+ that the exporter might wish to make available to buffer-users.
+
+ map_dma_buf() operation can return -EINTR if it is interrupted by a signal.
+
+
+5. When finished, the buffer-user notifies end-of-DMA to exporter
+
+ Once the DMA for the current buffer-user is over, it signals 'end-of-DMA' to
+ the exporter using the dma_buf_unmap_attachment API.
+
+ Interface:
+ void dma_buf_unmap_attachment(struct dma_buf_attachment *,
+ struct sg_table *);
+
+ This is a wrapper to dma_buf->ops->unmap_dma_buf() operation, which hides the
+ "dma_buf->ops->" indirection from the users of this interface.
+
+ In struct dma_buf_ops, unmap_dma_buf is defined as
+ void (*unmap_dma_buf)(struct dma_buf_attachment *, struct sg_table *);
+
+ unmap_dma_buf signifies the end-of-DMA for the attachment provided. Like
+ map_dma_buf, this API also must be implemented by the exporter.
+
+
+6. when buffer-user is done using this buffer, it 'disconnects' itself from the
+ buffer.
+
+ After the buffer-user has no more interest in using this buffer, it should
+ disconnect itself from the buffer:
+
+ - it first detaches itself from the buffer.
+
+ Interface:
+ void dma_buf_detach(struct dma_buf *dmabuf,
+ struct dma_buf_attachment *dmabuf_attach);
+
+ This API removes the attachment from the list in dmabuf, and optionally calls
+ dma_buf->ops->detach(), if provided by exporter, for any housekeeping bits.
+
+ - Then, the buffer-user returns the buffer reference to exporter.
+
+ Interface:
+ void dma_buf_put(struct dma_buf *dmabuf);
+
+ This API then reduces the refcount for this buffer.
+
+ If, as a result of this call, the refcount becomes 0, the 'release' file
+ operation related to this fd is called. It calls the dmabuf->ops->release()
+ operation in turn, and frees the memory allocated for dmabuf when exported.
+
+NOTES:
+- Importance of attach-detach and {map,unmap}_dma_buf operation pairs
+ The attach-detach calls allow the exporter to figure out backing-storage
+ constraints for the currently-interested devices. This allows preferential
+ allocation, and/or migration of pages across different types of storage
+ available, if possible.
+
+ Bracketing of DMA access with {map,unmap}_dma_buf operations is essential
+ to allow just-in-time backing of storage, and migration mid-way through a
+ use-case.
+
+- Migration of backing storage if needed
+ If after
+ - at least one map_dma_buf has happened,
+ - and the backing storage has been allocated for this buffer,
+ another new buffer-user intends to attach itself to this buffer, it might
+ be allowed, if possible for the exporter.
+
+ In case it is allowed by the exporter:
+ if the new buffer-user has stricter 'backing-storage constraints', and the
+ exporter can handle these constraints, the exporter can just stall on the
+ map_dma_buf until all outstanding access is completed (as signalled by
+ unmap_dma_buf).
+ Once all users have finished accessing and have unmapped this buffer, the
+ exporter could potentially move the buffer to the stricter backing-storage,
+ and then allow further {map,unmap}_dma_buf operations from any buffer-user
+ from the migrated backing-storage.
+
+ If the exporter cannot fulfil the backing-storage constraints of the new
+ buffer-user device as requested, dma_buf_attach() would return an error to
+ denote non-compatibility of the new buffer-sharing request with the current
+ buffer.
+
+ If the exporter chooses not to allow an attach() operation once a
+ map_dma_buf() API has been called, it simply returns an error.
+
+Kernel cpu access to a dma-buf buffer object
+--------------------------------------------
+
+The motivation to allow cpu access from the kernel to a dma-buf object from the
+importers side are:
+- fallback operations, e.g. if the devices is connected to a usb bus and the
+ kernel needs to shuffle the data around first before sending it away.
+- full transparency for existing users on the importer side, i.e. userspace
+ should not notice the difference between a normal object from that subsystem
+ and an imported one backed by a dma-buf. This is really important for drm
+ opengl drivers that expect to still use all the existing upload/download
+ paths.
+
+Access to a dma_buf from the kernel context involves three steps:
+
+1. Prepare access, which invalidate any necessary caches and make the object
+ available for cpu access.
+2. Access the object page-by-page with the dma_buf map apis
+3. Finish access, which will flush any necessary cpu caches and free reserved
+ resources.
+
+1. Prepare access
+
+ Before an importer can access a dma_buf object with the cpu from the kernel
+ context, it needs to notify the exporter of the access that is about to
+ happen.
+
+ Interface:
+ int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
+ size_t start, size_t len,
+ enum dma_data_direction direction)
+
+ This allows the exporter to ensure that the memory is actually available for
+ cpu access - the exporter might need to allocate or swap-in and pin the
+ backing storage. The exporter also needs to ensure that cpu access is
+ coherent for the given range and access direction. The range and access
+ direction can be used by the exporter to optimize the cache flushing, i.e.
+ access outside of the range or with a different direction (read instead of
+ write) might return stale or even bogus data (e.g. when the exporter needs to
+ copy the data to temporary storage).
+
+ This step might fail, e.g. in oom conditions.
+
+2. Accessing the buffer
+
+ To support dma_buf objects residing in highmem cpu access is page-based using
+ an api similar to kmap. Accessing a dma_buf is done in aligned chunks of
+ PAGE_SIZE size. Before accessing a chunk it needs to be mapped, which returns
+ a pointer in kernel virtual address space. Afterwards the chunk needs to be
+ unmapped again. There is no limit on how often a given chunk can be mapped
+ and unmapped, i.e. the importer does not need to call begin_cpu_access again
+ before mapping the same chunk again.
+
+ Interfaces:
+ void *dma_buf_kmap(struct dma_buf *, unsigned long);
+ void dma_buf_kunmap(struct dma_buf *, unsigned long, void *);
+
+ There are also atomic variants of these interfaces. Like for kmap they
+ facilitate non-blocking fast-paths. Neither the importer nor the exporter (in
+ the callback) is allowed to block when using these.
+
+ Interfaces:
+ void *dma_buf_kmap_atomic(struct dma_buf *, unsigned long);
+ void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long, void *);
+
+ For importers all the restrictions of using kmap apply, like the limited
+ supply of kmap_atomic slots. Hence an importer shall only hold onto at most 2
+ atomic dma_buf kmaps at the same time (in any given process context).
+
+ dma_buf kmap calls outside of the range specified in begin_cpu_access are
+ undefined. If the range is not PAGE_SIZE aligned, kmap needs to succeed on
+ the partial chunks at the beginning and end but may return stale or bogus
+ data outside of the range (in these partial chunks).
+
+ Note that these calls need to always succeed. The exporter needs to complete
+ any preparations that might fail in begin_cpu_access.
+
+ For some cases the overhead of kmap can be too high, a vmap interface
+ is introduced. This interface should be used very carefully, as vmalloc
+ space is a limited resources on many architectures.
+
+ Interfaces:
+ void *dma_buf_vmap(struct dma_buf *dmabuf)
+ void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
+
+ The vmap call can fail if there is no vmap support in the exporter, or if it
+ runs out of vmalloc space. Fallback to kmap should be implemented. Note that
+ the dma-buf layer keeps a reference count for all vmap access and calls down
+ into the exporter's vmap function only when no vmapping exists, and only
+ unmaps it once. Protection against concurrent vmap/vunmap calls is provided
+ by taking the dma_buf->lock mutex.
+
+3. Finish access
+
+ When the importer is done accessing the range specified in begin_cpu_access,
+ it needs to announce this to the exporter (to facilitate cache flushing and
+ unpinning of any pinned resources). The result of any dma_buf kmap calls
+ after end_cpu_access is undefined.
+
+ Interface:
+ void dma_buf_end_cpu_access(struct dma_buf *dma_buf,
+ size_t start, size_t len,
+ enum dma_data_direction dir);
+
+
+Direct Userspace Access/mmap Support
+------------------------------------
+
+Being able to mmap an export dma-buf buffer object has 2 main use-cases:
+- CPU fallback processing in a pipeline and
+- supporting existing mmap interfaces in importers.
+
+1. CPU fallback processing in a pipeline
+
+ In many processing pipelines it is sometimes required that the cpu can access
+ the data in a dma-buf (e.g. for thumbnail creation, snapshots, ...). To avoid
+ the need to handle this specially in userspace frameworks for buffer sharing
+ it's ideal if the dma_buf fd itself can be used to access the backing storage
+ from userspace using mmap.
+
+ Furthermore Android's ION framework already supports this (and is otherwise
+ rather similar to dma-buf from a userspace consumer side with using fds as
+ handles, too). So it's beneficial to support this in a similar fashion on
+ dma-buf to have a good transition path for existing Android userspace.
+
+ No special interfaces, userspace simply calls mmap on the dma-buf fd.
+
+2. Supporting existing mmap interfaces in exporters
+
+ Similar to the motivation for kernel cpu access it is again important that
+ the userspace code of a given importing subsystem can use the same interfaces
+ with a imported dma-buf buffer object as with a native buffer object. This is
+ especially important for drm where the userspace part of contemporary OpenGL,
+ X, and other drivers is huge, and reworking them to use a different way to
+ mmap a buffer rather invasive.
+
+ The assumption in the current dma-buf interfaces is that redirecting the
+ initial mmap is all that's needed. A survey of some of the existing
+ subsystems shows that no driver seems to do any nefarious thing like syncing
+ up with outstanding asynchronous processing on the device or allocating
+ special resources at fault time. So hopefully this is good enough, since
+ adding interfaces to intercept pagefaults and allow pte shootdowns would
+ increase the complexity quite a bit.
+
+ Interface:
+ int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
+ unsigned long);
+
+ If the importing subsystem simply provides a special-purpose mmap call to set
+ up a mapping in userspace, calling do_mmap with dma_buf->file will equally
+ achieve that for a dma-buf object.
+
+3. Implementation notes for exporters
+
+ Because dma-buf buffers have invariant size over their lifetime, the dma-buf
+ core checks whether a vma is too large and rejects such mappings. The
+ exporter hence does not need to duplicate this check.
+
+ Because existing importing subsystems might presume coherent mappings for
+ userspace, the exporter needs to set up a coherent mapping. If that's not
+ possible, it needs to fake coherency by manually shooting down ptes when
+ leaving the cpu domain and flushing caches at fault time. Note that all the
+ dma_buf files share the same anon inode, hence the exporter needs to replace
+ the dma_buf file stored in vma->vm_file with it's own if pte shootdown is
+ required. This is because the kernel uses the underlying inode's address_space
+ for vma tracking (and hence pte tracking at shootdown time with
+ unmap_mapping_range).
+
+ If the above shootdown dance turns out to be too expensive in certain
+ scenarios, we can extend dma-buf with a more explicit cache tracking scheme
+ for userspace mappings. But the current assumption is that using mmap is
+ always a slower path, so some inefficiencies should be acceptable.
+
+ Exporters that shoot down mappings (for any reasons) shall not do any
+ synchronization at fault time with outstanding device operations.
+ Synchronization is an orthogonal issue to sharing the backing storage of a
+ buffer and hence should not be handled by dma-buf itself. This is explicitly
+ mentioned here because many people seem to want something like this, but if
+ different exporters handle this differently, buffer sharing can fail in
+ interesting ways depending upong the exporter (if userspace starts depending
+ upon this implicit synchronization).
+
+Other Interfaces Exposed to Userspace on the dma-buf FD
+------------------------------------------------------
+
+- Since kernel 3.12 the dma-buf FD supports the llseek system call, but only
+ with offset=0 and whence=SEEK_END|SEEK_SET. SEEK_SET is supported to allow
+ the usual size discover pattern size = SEEK_END(0); SEEK_SET(0). Every other
+ llseek operation will report -EINVAL.
+
+ If llseek on dma-buf FDs isn't support the kernel will report -ESPIPE for all
+ cases. Userspace can use this to detect support for discovering the dma-buf
+ size using llseek.
+
+Miscellaneous notes
+-------------------
+
+- Any exporters or users of the dma-buf buffer sharing framework must have
+ a 'select DMA_SHARED_BUFFER' in their respective Kconfigs.
+
+- In order to avoid fd leaks on exec, the FD_CLOEXEC flag must be set
+ on the file descriptor. This is not just a resource leak, but a
+ potential security hole. It could give the newly exec'd application
+ access to buffers, via the leaked fd, to which it should otherwise
+ not be permitted access.
+
+ The problem with doing this via a separate fcntl() call, versus doing it
+ atomically when the fd is created, is that this is inherently racy in a
+ multi-threaded app[3]. The issue is made worse when it is library code
+ opening/creating the file descriptor, as the application may not even be
+ aware of the fd's.
+
+ To avoid this problem, userspace must have a way to request O_CLOEXEC
+ flag be set when the dma-buf fd is created. So any API provided by
+ the exporting driver to create a dmabuf fd must provide a way to let
+ userspace control setting of O_CLOEXEC flag passed in to dma_buf_fd().
+
+- If an exporter needs to manually flush caches and hence needs to fake
+ coherency for mmap support, it needs to be able to zap all the ptes pointing
+ at the backing storage. Now linux mm needs a struct address_space associated
+ with the struct file stored in vma->vm_file to do that with the function
+ unmap_mapping_range. But the dma_buf framework only backs every dma_buf fd
+ with the anon_file struct file, i.e. all dma_bufs share the same file.
+
+ Hence exporters need to setup their own file (and address_space) association
+ by setting vma->vm_file and adjusting vma->vm_pgoff in the dma_buf mmap
+ callback. In the specific case of a gem driver the exporter could use the
+ shmem file already provided by gem (and set vm_pgoff = 0). Exporters can then
+ zap ptes by unmapping the corresponding range of the struct address_space
+ associated with their own file.
+
+References:
+[1] struct dma_buf_ops in include/linux/dma-buf.h
+[2] All interfaces mentioned above defined in include/linux/dma-buf.h
+[3] https://lwn.net/Articles/236486/
diff --git a/Documentation/dma/dmaengine.txt b/Documentation/dma/dmaengine.txt
new file mode 100644
index 0000000..879b6e3
--- /dev/null
+++ b/Documentation/dma/dmaengine.txt
@@ -0,0 +1,198 @@
+ DMA Engine API Guide
+ ====================
+
+ Vinod Koul <vinod dot koul at intel.com>
+
+NOTE: For DMA Engine usage in async_tx please see:
+ Documentation/crypto/async-tx-api.txt
+
+
+Below is a guide to device driver writers on how to use the Slave-DMA API of the
+DMA Engine. This is applicable only for slave DMA usage only.
+
+The slave DMA usage consists of following steps:
+1. Allocate a DMA slave channel
+2. Set slave and controller specific parameters
+3. Get a descriptor for transaction
+4. Submit the transaction
+5. Issue pending requests and wait for callback notification
+
+1. Allocate a DMA slave channel
+
+ Channel allocation is slightly different in the slave DMA context,
+ client drivers typically need a channel from a particular DMA
+ controller only and even in some cases a specific channel is desired.
+ To request a channel dma_request_channel() API is used.
+
+ Interface:
+ struct dma_chan *dma_request_channel(dma_cap_mask_t mask,
+ dma_filter_fn filter_fn,
+ void *filter_param);
+ where dma_filter_fn is defined as:
+ typedef bool (*dma_filter_fn)(struct dma_chan *chan, void *filter_param);
+
+ The 'filter_fn' parameter is optional, but highly recommended for
+ slave and cyclic channels as they typically need to obtain a specific
+ DMA channel.
+
+ When the optional 'filter_fn' parameter is NULL, dma_request_channel()
+ simply returns the first channel that satisfies the capability mask.
+
+ Otherwise, the 'filter_fn' routine will be called once for each free
+ channel which has a capability in 'mask'. 'filter_fn' is expected to
+ return 'true' when the desired DMA channel is found.
+
+ A channel allocated via this interface is exclusive to the caller,
+ until dma_release_channel() is called.
+
+2. Set slave and controller specific parameters
+
+ Next step is always to pass some specific information to the DMA
+ driver. Most of the generic information which a slave DMA can use
+ is in struct dma_slave_config. This allows the clients to specify
+ DMA direction, DMA addresses, bus widths, DMA burst lengths etc
+ for the peripheral.
+
+ If some DMA controllers have more parameters to be sent then they
+ should try to embed struct dma_slave_config in their controller
+ specific structure. That gives flexibility to client to pass more
+ parameters, if required.
+
+ Interface:
+ int dmaengine_slave_config(struct dma_chan *chan,
+ struct dma_slave_config *config)
+
+ Please see the dma_slave_config structure definition in dmaengine.h
+ for a detailed explanation of the struct members. Please note
+ that the 'direction' member will be going away as it duplicates the
+ direction given in the prepare call.
+
+3. Get a descriptor for transaction
+
+ For slave usage the various modes of slave transfers supported by the
+ DMA-engine are:
+
+ slave_sg - DMA a list of scatter gather buffers from/to a peripheral
+ dma_cyclic - Perform a cyclic DMA operation from/to a peripheral till the
+ operation is explicitly stopped.
+ interleaved_dma - This is common to Slave as well as M2M clients. For slave
+ address of devices' fifo could be already known to the driver.
+ Various types of operations could be expressed by setting
+ appropriate values to the 'dma_interleaved_template' members.
+
+ A non-NULL return of this transfer API represents a "descriptor" for
+ the given transaction.
+
+ Interface:
+ struct dma_async_tx_descriptor *(*chan->device->device_prep_slave_sg)(
+ struct dma_chan *chan, struct scatterlist *sgl,
+ unsigned int sg_len, enum dma_data_direction direction,
+ unsigned long flags);
+
+ struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_cyclic)(
+ struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
+ size_t period_len, enum dma_data_direction direction);
+
+ struct dma_async_tx_descriptor *(*device_prep_interleaved_dma)(
+ struct dma_chan *chan, struct dma_interleaved_template *xt,
+ unsigned long flags);
+
+ The peripheral driver is expected to have mapped the scatterlist for
+ the DMA operation prior to calling device_prep_slave_sg, and must
+ keep the scatterlist mapped until the DMA operation has completed.
+ The scatterlist must be mapped using the DMA struct device. So,
+ normal setup should look like this:
+
+ nr_sg = dma_map_sg(chan->device->dev, sgl, sg_len);
+ if (nr_sg == 0)
+ /* error */
+
+ desc = chan->device->device_prep_slave_sg(chan, sgl, nr_sg,
+ direction, flags);
+
+ Once a descriptor has been obtained, the callback information can be
+ added and the descriptor must then be submitted. Some DMA engine
+ drivers may hold a spinlock between a successful preparation and
+ submission so it is important that these two operations are closely
+ paired.
+
+ Note:
+ Although the async_tx API specifies that completion callback
+ routines cannot submit any new operations, this is not the
+ case for slave/cyclic DMA.
+
+ For slave DMA, the subsequent transaction may not be available
+ for submission prior to callback function being invoked, so
+ slave DMA callbacks are permitted to prepare and submit a new
+ transaction.
+
+ For cyclic DMA, a callback function may wish to terminate the
+ DMA via dmaengine_terminate_all().
+
+ Therefore, it is important that DMA engine drivers drop any
+ locks before calling the callback function which may cause a
+ deadlock.
+
+ Note that callbacks will always be invoked from the DMA
+ engines tasklet, never from interrupt context.
+
+4. Submit the transaction
+
+ Once the descriptor has been prepared and the callback information
+ added, it must be placed on the DMA engine drivers pending queue.
+
+ Interface:
+ dma_cookie_t dmaengine_submit(struct dma_async_tx_descriptor *desc)
+
+ This returns a cookie can be used to check the progress of DMA engine
+ activity via other DMA engine calls not covered in this document.
+
+ dmaengine_submit() will not start the DMA operation, it merely adds
+ it to the pending queue. For this, see step 5, dma_async_issue_pending.
+
+5. Issue pending DMA requests and wait for callback notification
+
+ The transactions in the pending queue can be activated by calling the
+ issue_pending API. If channel is idle then the first transaction in
+ queue is started and subsequent ones queued up.
+
+ On completion of each DMA operation, the next in queue is started and
+ a tasklet triggered. The tasklet will then call the client driver
+ completion callback routine for notification, if set.
+
+ Interface:
+ void dma_async_issue_pending(struct dma_chan *chan);
+
+Further APIs:
+
+1. int dmaengine_terminate_all(struct dma_chan *chan)
+
+ This causes all activity for the DMA channel to be stopped, and may
+ discard data in the DMA FIFO which hasn't been fully transferred.
+ No callback functions will be called for any incomplete transfers.
+
+2. int dmaengine_pause(struct dma_chan *chan)
+
+ This pauses activity on the DMA channel without data loss.
+
+3. int dmaengine_resume(struct dma_chan *chan)
+
+ Resume a previously paused DMA channel. It is invalid to resume a
+ channel which is not currently paused.
+
+4. enum dma_status dma_async_is_tx_complete(struct dma_chan *chan,
+ dma_cookie_t cookie, dma_cookie_t *last, dma_cookie_t *used)
+
+ This can be used to check the status of the channel. Please see
+ the documentation in include/linux/dmaengine.h for a more complete
+ description of this API.
+
+ This can be used in conjunction with dma_async_is_complete() and
+ the cookie returned from 'descriptor->submit()' to check for
+ completion of a specific DMA transaction.
+
+ Note:
+ Not all DMA engine drivers can return reliable information for
+ a running DMA channel. It is recommended that DMA engine users
+ pause or stop (via dmaengine_terminate_all) the channel before
+ using this API.
diff --git a/Documentation/dma/dmatest.txt b/Documentation/dma/dmatest.txt
new file mode 100644
index 0000000..dd77a81
--- /dev/null
+++ b/Documentation/dma/dmatest.txt
@@ -0,0 +1,92 @@
+ DMA Test Guide
+ ==============
+
+ Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
+
+This small document introduces how to test DMA drivers using dmatest module.
+
+ Part 1 - How to build the test module
+
+The menuconfig contains an option that could be found by following path:
+ Device Drivers -> DMA Engine support -> DMA Test client
+
+In the configuration file the option called CONFIG_DMATEST. The dmatest could
+be built as module or inside kernel. Let's consider those cases.
+
+ Part 2 - When dmatest is built as a module...
+
+Example of usage:
+ % modprobe dmatest channel=dma0chan0 timeout=2000 iterations=1 run=1
+
+...or:
+ % modprobe dmatest
+ % echo dma0chan0 > /sys/module/dmatest/parameters/channel
+ % echo 2000 > /sys/module/dmatest/parameters/timeout
+ % echo 1 > /sys/module/dmatest/parameters/iterations
+ % echo 1 > /sys/module/dmatest/parameters/run
+
+...or on the kernel command line:
+
+ dmatest.channel=dma0chan0 dmatest.timeout=2000 dmatest.iterations=1 dmatest.run=1
+
+Hint: available channel list could be extracted by running the following
+command:
+ % ls -1 /sys/class/dma/
+
+Once started a message like "dmatest: Started 1 threads using dma0chan0" is
+emitted. After that only test failure messages are reported until the test
+stops.
+
+Note that running a new test will not stop any in progress test.
+
+The following command returns the state of the test.
+ % cat /sys/module/dmatest/parameters/run
+
+To wait for test completion userpace can poll 'run' until it is false, or use
+the wait parameter. Specifying 'wait=1' when loading the module causes module
+initialization to pause until a test run has completed, while reading
+/sys/module/dmatest/parameters/wait waits for any running test to complete
+before returning. For example, the following scripts wait for 42 tests
+to complete before exiting. Note that if 'iterations' is set to 'infinite' then
+waiting is disabled.
+
+Example:
+ % modprobe dmatest run=1 iterations=42 wait=1
+ % modprobe -r dmatest
+...or:
+ % modprobe dmatest run=1 iterations=42
+ % cat /sys/module/dmatest/parameters/wait
+ % modprobe -r dmatest
+
+ Part 3 - When built-in in the kernel...
+
+The module parameters that is supplied to the kernel command line will be used
+for the first performed test. After user gets a control, the test could be
+re-run with the same or different parameters. For the details see the above
+section "Part 2 - When dmatest is built as a module..."
+
+In both cases the module parameters are used as the actual values for the test
+case. You always could check them at run-time by running
+ % grep -H . /sys/module/dmatest/parameters/*
+
+ Part 4 - Gathering the test results
+
+Test results are printed to the kernel log buffer with the format:
+
+"dmatest: result <channel>: <test id>: '<error msg>' with src_off=<val> dst_off=<val> len=<val> (<err code>)"
+
+Example of output:
+ % dmesg | tail -n 1
+ dmatest: result dma0chan0-copy0: #1: No errors with src_off=0x7bf dst_off=0x8ad len=0x3fea (0)
+
+The message format is unified across the different types of errors. A number in
+the parens represents additional information, e.g. error code, error counter,
+or status. A test thread also emits a summary line at completion listing the
+number of tests executed, number that failed, and a result code.
+
+Example:
+ % dmesg | tail -n 1
+ dmatest: dma0chan0-copy0: summary 1 test, 0 failures 1000 iops 100000 KB/s (0)
+
+The details of a data miscompare error are also emitted, but do not follow the
+above format.
diff --git a/Documentation/dmaengine.txt b/Documentation/dmaengine.txt
deleted file mode 100644
index 879b6e3..0000000
--- a/Documentation/dmaengine.txt
+++ /dev/null
@@ -1,198 +0,0 @@
- DMA Engine API Guide
- ====================
-
- Vinod Koul <vinod dot koul at intel.com>
-
-NOTE: For DMA Engine usage in async_tx please see:
- Documentation/crypto/async-tx-api.txt
-
-
-Below is a guide to device driver writers on how to use the Slave-DMA API of the
-DMA Engine. This is applicable only for slave DMA usage only.
-
-The slave DMA usage consists of following steps:
-1. Allocate a DMA slave channel
-2. Set slave and controller specific parameters
-3. Get a descriptor for transaction
-4. Submit the transaction
-5. Issue pending requests and wait for callback notification
-
-1. Allocate a DMA slave channel
-
- Channel allocation is slightly different in the slave DMA context,
- client drivers typically need a channel from a particular DMA
- controller only and even in some cases a specific channel is desired.
- To request a channel dma_request_channel() API is used.
-
- Interface:
- struct dma_chan *dma_request_channel(dma_cap_mask_t mask,
- dma_filter_fn filter_fn,
- void *filter_param);
- where dma_filter_fn is defined as:
- typedef bool (*dma_filter_fn)(struct dma_chan *chan, void *filter_param);
-
- The 'filter_fn' parameter is optional, but highly recommended for
- slave and cyclic channels as they typically need to obtain a specific
- DMA channel.
-
- When the optional 'filter_fn' parameter is NULL, dma_request_channel()
- simply returns the first channel that satisfies the capability mask.
-
- Otherwise, the 'filter_fn' routine will be called once for each free
- channel which has a capability in 'mask'. 'filter_fn' is expected to
- return 'true' when the desired DMA channel is found.
-
- A channel allocated via this interface is exclusive to the caller,
- until dma_release_channel() is called.
-
-2. Set slave and controller specific parameters
-
- Next step is always to pass some specific information to the DMA
- driver. Most of the generic information which a slave DMA can use
- is in struct dma_slave_config. This allows the clients to specify
- DMA direction, DMA addresses, bus widths, DMA burst lengths etc
- for the peripheral.
-
- If some DMA controllers have more parameters to be sent then they
- should try to embed struct dma_slave_config in their controller
- specific structure. That gives flexibility to client to pass more
- parameters, if required.
-
- Interface:
- int dmaengine_slave_config(struct dma_chan *chan,
- struct dma_slave_config *config)
-
- Please see the dma_slave_config structure definition in dmaengine.h
- for a detailed explanation of the struct members. Please note
- that the 'direction' member will be going away as it duplicates the
- direction given in the prepare call.
-
-3. Get a descriptor for transaction
-
- For slave usage the various modes of slave transfers supported by the
- DMA-engine are:
-
- slave_sg - DMA a list of scatter gather buffers from/to a peripheral
- dma_cyclic - Perform a cyclic DMA operation from/to a peripheral till the
- operation is explicitly stopped.
- interleaved_dma - This is common to Slave as well as M2M clients. For slave
- address of devices' fifo could be already known to the driver.
- Various types of operations could be expressed by setting
- appropriate values to the 'dma_interleaved_template' members.
-
- A non-NULL return of this transfer API represents a "descriptor" for
- the given transaction.
-
- Interface:
- struct dma_async_tx_descriptor *(*chan->device->device_prep_slave_sg)(
- struct dma_chan *chan, struct scatterlist *sgl,
- unsigned int sg_len, enum dma_data_direction direction,
- unsigned long flags);
-
- struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_cyclic)(
- struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
- size_t period_len, enum dma_data_direction direction);
-
- struct dma_async_tx_descriptor *(*device_prep_interleaved_dma)(
- struct dma_chan *chan, struct dma_interleaved_template *xt,
- unsigned long flags);
-
- The peripheral driver is expected to have mapped the scatterlist for
- the DMA operation prior to calling device_prep_slave_sg, and must
- keep the scatterlist mapped until the DMA operation has completed.
- The scatterlist must be mapped using the DMA struct device. So,
- normal setup should look like this:
-
- nr_sg = dma_map_sg(chan->device->dev, sgl, sg_len);
- if (nr_sg == 0)
- /* error */
-
- desc = chan->device->device_prep_slave_sg(chan, sgl, nr_sg,
- direction, flags);
-
- Once a descriptor has been obtained, the callback information can be
- added and the descriptor must then be submitted. Some DMA engine
- drivers may hold a spinlock between a successful preparation and
- submission so it is important that these two operations are closely
- paired.
-
- Note:
- Although the async_tx API specifies that completion callback
- routines cannot submit any new operations, this is not the
- case for slave/cyclic DMA.
-
- For slave DMA, the subsequent transaction may not be available
- for submission prior to callback function being invoked, so
- slave DMA callbacks are permitted to prepare and submit a new
- transaction.
-
- For cyclic DMA, a callback function may wish to terminate the
- DMA via dmaengine_terminate_all().
-
- Therefore, it is important that DMA engine drivers drop any
- locks before calling the callback function which may cause a
- deadlock.
-
- Note that callbacks will always be invoked from the DMA
- engines tasklet, never from interrupt context.
-
-4. Submit the transaction
-
- Once the descriptor has been prepared and the callback information
- added, it must be placed on the DMA engine drivers pending queue.
-
- Interface:
- dma_cookie_t dmaengine_submit(struct dma_async_tx_descriptor *desc)
-
- This returns a cookie can be used to check the progress of DMA engine
- activity via other DMA engine calls not covered in this document.
-
- dmaengine_submit() will not start the DMA operation, it merely adds
- it to the pending queue. For this, see step 5, dma_async_issue_pending.
-
-5. Issue pending DMA requests and wait for callback notification
-
- The transactions in the pending queue can be activated by calling the
- issue_pending API. If channel is idle then the first transaction in
- queue is started and subsequent ones queued up.
-
- On completion of each DMA operation, the next in queue is started and
- a tasklet triggered. The tasklet will then call the client driver
- completion callback routine for notification, if set.
-
- Interface:
- void dma_async_issue_pending(struct dma_chan *chan);
-
-Further APIs:
-
-1. int dmaengine_terminate_all(struct dma_chan *chan)
-
- This causes all activity for the DMA channel to be stopped, and may
- discard data in the DMA FIFO which hasn't been fully transferred.
- No callback functions will be called for any incomplete transfers.
-
-2. int dmaengine_pause(struct dma_chan *chan)
-
- This pauses activity on the DMA channel without data loss.
-
-3. int dmaengine_resume(struct dma_chan *chan)
-
- Resume a previously paused DMA channel. It is invalid to resume a
- channel which is not currently paused.
-
-4. enum dma_status dma_async_is_tx_complete(struct dma_chan *chan,
- dma_cookie_t cookie, dma_cookie_t *last, dma_cookie_t *used)
-
- This can be used to check the status of the channel. Please see
- the documentation in include/linux/dmaengine.h for a more complete
- description of this API.
-
- This can be used in conjunction with dma_async_is_complete() and
- the cookie returned from 'descriptor->submit()' to check for
- completion of a specific DMA transaction.
-
- Note:
- Not all DMA engine drivers can return reliable information for
- a running DMA channel. It is recommended that DMA engine users
- pause or stop (via dmaengine_terminate_all) the channel before
- using this API.
diff --git a/Documentation/dmatest.txt b/Documentation/dmatest.txt
deleted file mode 100644
index dd77a81..0000000
--- a/Documentation/dmatest.txt
+++ /dev/null
@@ -1,92 +0,0 @@
- DMA Test Guide
- ==============
-
- Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
-
-This small document introduces how to test DMA drivers using dmatest module.
-
- Part 1 - How to build the test module
-
-The menuconfig contains an option that could be found by following path:
- Device Drivers -> DMA Engine support -> DMA Test client
-
-In the configuration file the option called CONFIG_DMATEST. The dmatest could
-be built as module or inside kernel. Let's consider those cases.
-
- Part 2 - When dmatest is built as a module...
-
-Example of usage:
- % modprobe dmatest channel=dma0chan0 timeout=2000 iterations=1 run=1
-
-...or:
- % modprobe dmatest
- % echo dma0chan0 > /sys/module/dmatest/parameters/channel
- % echo 2000 > /sys/module/dmatest/parameters/timeout
- % echo 1 > /sys/module/dmatest/parameters/iterations
- % echo 1 > /sys/module/dmatest/parameters/run
-
-...or on the kernel command line:
-
- dmatest.channel=dma0chan0 dmatest.timeout=2000 dmatest.iterations=1 dmatest.run=1
-
-Hint: available channel list could be extracted by running the following
-command:
- % ls -1 /sys/class/dma/
-
-Once started a message like "dmatest: Started 1 threads using dma0chan0" is
-emitted. After that only test failure messages are reported until the test
-stops.
-
-Note that running a new test will not stop any in progress test.
-
-The following command returns the state of the test.
- % cat /sys/module/dmatest/parameters/run
-
-To wait for test completion userpace can poll 'run' until it is false, or use
-the wait parameter. Specifying 'wait=1' when loading the module causes module
-initialization to pause until a test run has completed, while reading
-/sys/module/dmatest/parameters/wait waits for any running test to complete
-before returning. For example, the following scripts wait for 42 tests
-to complete before exiting. Note that if 'iterations' is set to 'infinite' then
-waiting is disabled.
-
-Example:
- % modprobe dmatest run=1 iterations=42 wait=1
- % modprobe -r dmatest
-...or:
- % modprobe dmatest run=1 iterations=42
- % cat /sys/module/dmatest/parameters/wait
- % modprobe -r dmatest
-
- Part 3 - When built-in in the kernel...
-
-The module parameters that is supplied to the kernel command line will be used
-for the first performed test. After user gets a control, the test could be
-re-run with the same or different parameters. For the details see the above
-section "Part 2 - When dmatest is built as a module..."
-
-In both cases the module parameters are used as the actual values for the test
-case. You always could check them at run-time by running
- % grep -H . /sys/module/dmatest/parameters/*
-
- Part 4 - Gathering the test results
-
-Test results are printed to the kernel log buffer with the format:
-
-"dmatest: result <channel>: <test id>: '<error msg>' with src_off=<val> dst_off=<val> len=<val> (<err code>)"
-
-Example of output:
- % dmesg | tail -n 1
- dmatest: result dma0chan0-copy0: #1: No errors with src_off=0x7bf dst_off=0x8ad len=0x3fea (0)
-
-The message format is unified across the different types of errors. A number in
-the parens represents additional information, e.g. error code, error counter,
-or status. A test thread also emits a summary line at completion listing the
-number of tests executed, number that failed, and a result code.
-
-Example:
- % dmesg | tail -n 1
- dmatest: dma0chan0-copy0: summary 1 test, 0 failures 1000 iops 100000 KB/s (0)
-
-The details of a data miscompare error are also emitted, but do not follow the
-above format.
--
1.7.9.5
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