Re: [099/244] PCI: Set PCI-E Max Payload Size on fabric
From: Bjorn Helgaas
Date: Fri Sep 30 2011 - 18:34:03 EST
On Wed, Sep 28, 2011 at 4:01 PM, Greg KH <gregkh@xxxxxxx> wrote:
> 3.0-stable review patch. If anyone has any objections, please let us know.
I object to this :) I think the following patches should be omitted
from -stable:
[099/244] PCI: Set PCI-E Max Payload Size on fabric
[100/244] PCI: export pcie_bus_configure_settings symbol
[101/244] PCI: Remove MRRS modification from MPS setting code
[212/244] pci: Dont crash when reading mpss from root complex
I've heard rumors that these patches are required to make 3.0 boot on
some machines, but I don't really believe it, and I haven't seen the
problem reports myself.
Also, these patches introduce an open regression (Avi's e1000e
problem). Jon has mooted a patch that we hope will fix the
regression, but I'm still not confident that this is all safe for 3.1,
much less 3.0-stable.
> ------------------
>
> From: Jon Mason <mason@xxxxxxxx>
>
> commit b03e7495a862b028294f59fc87286d6d78ee7fa1 upstream.
>
> On a given PCI-E fabric, each device, bridge, and root port can have a
> different PCI-E maximum payload size. There is a sizable performance
> boost for having the largest possible maximum payload size on each PCI-E
> device. However, if improperly configured, fatal bus errors can occur.
> Thus, it is important to ensure that PCI-E payloads sends by a device
> are never larger than the MPS setting of all devices on the way to the
> destination.
>
> This can be achieved two ways:
>
> - A conservative approach is to use the smallest common denominator of
> the entire tree below a root complex for every device on that fabric.
>
> This means for example that having a 128 bytes MPS USB controller on one
> leg of a switch will dramatically reduce performances of a video card or
> 10GE adapter on another leg of that same switch.
>
> It also means that any hierarchy supporting hotplug slots (including
> expresscard or thunderbolt I suppose, dbl check that) will have to be
> entirely clamped to 128 bytes since we cannot predict what will be
> plugged into those slots, and we cannot change the MPS on a "live"
> system.
>
> - A more optimal way is possible, if it falls within a couple of
> constraints:
> * The top-level host bridge will never generate packets larger than the
> smallest TLP (or if it can be controlled independently from its MPS at
> least)
> * The device will never generate packets larger than MPS (which can be
> configured via MRRS)
> * No support of direct PCI-E <-> PCI-E transfers between devices without
> some additional code to specifically deal with that case
>
> Then we can use an approach that basically ignores downstream requests
> and focuses exclusively on upstream requests. In that case, all we need
> to care about is that a device MPS is no larger than its parent MPS,
> which allows us to keep all switches/bridges to the max MPS supported by
> their parent and eventually the PHB.
>
> In this case, your USB controller would no longer "starve" your 10GE
> Ethernet and your hotplug slots won't affect your global MPS.
> Additionally, the hotplugged devices themselves can be configured to a
> larger MPS up to the value configured in the hotplug bridge.
>
> To choose between the two available options, two PCI kernel boot args
> have been added to the PCI calls. "pcie_bus_safe" will provide the
> former behavior, while "pcie_bus_perf" will perform the latter behavior.
> By default, the latter behavior is used.
>
> NOTE: due to the location of the enablement, each arch will need to add
> calls to this function. This patch only enables x86.
>
> This patch includes a number of changes recommended by Benjamin
> Herrenschmidt.
>
> Tested-by: Jordan_Hargrave@xxxxxxxx
> Signed-off-by: Jon Mason <mason@xxxxxxxx>
> Signed-off-by: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
>
> ---
> arch/x86/pci/acpi.c | 9 ++
> drivers/pci/hotplug/pcihp_slot.c | 45 ------------
> drivers/pci/pci.c | 67 ++++++++++++++++++
> drivers/pci/probe.c | 145 +++++++++++++++++++++++++++++++++++++++
> include/linux/pci.h | 15 +++-
> 5 files changed, 236 insertions(+), 45 deletions(-)
>
> --- a/arch/x86/pci/acpi.c
> +++ b/arch/x86/pci/acpi.c
> @@ -361,6 +361,15 @@ struct pci_bus * __devinit pci_acpi_scan
> }
> }
>
> + /* After the PCI-E bus has been walked and all devices discovered,
> + * configure any settings of the fabric that might be necessary.
> + */
> + if (bus) {
> + struct pci_bus *child;
> + list_for_each_entry(child, &bus->children, node)
> + pcie_bus_configure_settings(child, child->self->pcie_mpss);
> + }
> +
> if (!bus)
> kfree(sd);
>
> --- a/drivers/pci/hotplug/pcihp_slot.c
> +++ b/drivers/pci/hotplug/pcihp_slot.c
> @@ -158,47 +158,6 @@ static void program_hpp_type2(struct pci
> */
> }
>
> -/* Program PCIE MaxPayload setting on device: ensure parent maxpayload <= device */
> -static int pci_set_payload(struct pci_dev *dev)
> -{
> - int pos, ppos;
> - u16 pctl, psz;
> - u16 dctl, dsz, dcap, dmax;
> - struct pci_dev *parent;
> -
> - parent = dev->bus->self;
> - pos = pci_find_capability(dev, PCI_CAP_ID_EXP);
> - if (!pos)
> - return 0;
> -
> - /* Read Device MaxPayload capability and setting */
> - pci_read_config_word(dev, pos + PCI_EXP_DEVCTL, &dctl);
> - pci_read_config_word(dev, pos + PCI_EXP_DEVCAP, &dcap);
> - dsz = (dctl & PCI_EXP_DEVCTL_PAYLOAD) >> 5;
> - dmax = (dcap & PCI_EXP_DEVCAP_PAYLOAD);
> -
> - /* Read Parent MaxPayload setting */
> - ppos = pci_find_capability(parent, PCI_CAP_ID_EXP);
> - if (!ppos)
> - return 0;
> - pci_read_config_word(parent, ppos + PCI_EXP_DEVCTL, &pctl);
> - psz = (pctl & PCI_EXP_DEVCTL_PAYLOAD) >> 5;
> -
> - /* If parent payload > device max payload -> error
> - * If parent payload > device payload -> set speed
> - * If parent payload <= device payload -> do nothing
> - */
> - if (psz > dmax)
> - return -1;
> - else if (psz > dsz) {
> - dev_info(&dev->dev, "Setting MaxPayload to %d\n", 128 << psz);
> - pci_write_config_word(dev, pos + PCI_EXP_DEVCTL,
> - (dctl & ~PCI_EXP_DEVCTL_PAYLOAD) +
> - (psz << 5));
> - }
> - return 0;
> -}
> -
> void pci_configure_slot(struct pci_dev *dev)
> {
> struct pci_dev *cdev;
> @@ -210,9 +169,7 @@ void pci_configure_slot(struct pci_dev *
> (dev->class >> 8) == PCI_CLASS_BRIDGE_PCI)))
> return;
>
> - ret = pci_set_payload(dev);
> - if (ret)
> - dev_warn(&dev->dev, "could not set device max payload\n");
> + pcie_bus_configure_settings(dev->bus, dev->bus->self->pcie_mpss);
>
> memset(&hpp, 0, sizeof(hpp));
> ret = pci_get_hp_params(dev, &hpp);
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -77,6 +77,8 @@ unsigned long pci_cardbus_mem_size = DEF
> unsigned long pci_hotplug_io_size = DEFAULT_HOTPLUG_IO_SIZE;
> unsigned long pci_hotplug_mem_size = DEFAULT_HOTPLUG_MEM_SIZE;
>
> +enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_PERFORMANCE;
> +
> /*
> * The default CLS is used if arch didn't set CLS explicitly and not
> * all pci devices agree on the same value. Arch can override either
> @@ -3223,6 +3225,67 @@ out:
> EXPORT_SYMBOL(pcie_set_readrq);
>
> /**
> + * pcie_get_mps - get PCI Express maximum payload size
> + * @dev: PCI device to query
> + *
> + * Returns maximum payload size in bytes
> + * or appropriate error value.
> + */
> +int pcie_get_mps(struct pci_dev *dev)
> +{
> + int ret, cap;
> + u16 ctl;
> +
> + cap = pci_pcie_cap(dev);
> + if (!cap)
> + return -EINVAL;
> +
> + ret = pci_read_config_word(dev, cap + PCI_EXP_DEVCTL, &ctl);
> + if (!ret)
> + ret = 128 << ((ctl & PCI_EXP_DEVCTL_PAYLOAD) >> 5);
> +
> + return ret;
> +}
> +
> +/**
> + * pcie_set_mps - set PCI Express maximum payload size
> + * @dev: PCI device to query
> + * @rq: maximum payload size in bytes
> + * valid values are 128, 256, 512, 1024, 2048, 4096
> + *
> + * If possible sets maximum payload size
> + */
> +int pcie_set_mps(struct pci_dev *dev, int mps)
> +{
> + int cap, err = -EINVAL;
> + u16 ctl, v;
> +
> + if (mps < 128 || mps > 4096 || !is_power_of_2(mps))
> + goto out;
> +
> + v = ffs(mps) - 8;
> + if (v > dev->pcie_mpss)
> + goto out;
> + v <<= 5;
> +
> + cap = pci_pcie_cap(dev);
> + if (!cap)
> + goto out;
> +
> + err = pci_read_config_word(dev, cap + PCI_EXP_DEVCTL, &ctl);
> + if (err)
> + goto out;
> +
> + if ((ctl & PCI_EXP_DEVCTL_PAYLOAD) != v) {
> + ctl &= ~PCI_EXP_DEVCTL_PAYLOAD;
> + ctl |= v;
> + err = pci_write_config_word(dev, cap + PCI_EXP_DEVCTL, ctl);
> + }
> +out:
> + return err;
> +}
> +
> +/**
> * pci_select_bars - Make BAR mask from the type of resource
> * @dev: the PCI device for which BAR mask is made
> * @flags: resource type mask to be selected
> @@ -3505,6 +3568,10 @@ static int __init pci_setup(char *str)
> pci_hotplug_io_size = memparse(str + 9, &str);
> } else if (!strncmp(str, "hpmemsize=", 10)) {
> pci_hotplug_mem_size = memparse(str + 10, &str);
> + } else if (!strncmp(str, "pcie_bus_safe", 13)) {
> + pcie_bus_config = PCIE_BUS_SAFE;
> + } else if (!strncmp(str, "pcie_bus_perf", 13)) {
> + pcie_bus_config = PCIE_BUS_PERFORMANCE;
> } else {
> printk(KERN_ERR "PCI: Unknown option `%s'\n",
> str);
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -860,6 +860,8 @@ void set_pcie_port_type(struct pci_dev *
> pdev->pcie_cap = pos;
> pci_read_config_word(pdev, pos + PCI_EXP_FLAGS, ®16);
> pdev->pcie_type = (reg16 & PCI_EXP_FLAGS_TYPE) >> 4;
> + pci_read_config_word(pdev, pos + PCI_EXP_DEVCAP, ®16);
> + pdev->pcie_mpss = reg16 & PCI_EXP_DEVCAP_PAYLOAD;
> }
>
> void set_pcie_hotplug_bridge(struct pci_dev *pdev)
> @@ -1327,6 +1329,149 @@ int pci_scan_slot(struct pci_bus *bus, i
> return nr;
> }
>
> +static int pcie_find_smpss(struct pci_dev *dev, void *data)
> +{
> + u8 *smpss = data;
> +
> + if (!pci_is_pcie(dev))
> + return 0;
> +
> + /* For PCIE hotplug enabled slots not connected directly to a
> + * PCI-E root port, there can be problems when hotplugging
> + * devices. This is due to the possibility of hotplugging a
> + * device into the fabric with a smaller MPS that the devices
> + * currently running have configured. Modifying the MPS on the
> + * running devices could cause a fatal bus error due to an
> + * incoming frame being larger than the newly configured MPS.
> + * To work around this, the MPS for the entire fabric must be
> + * set to the minimum size. Any devices hotplugged into this
> + * fabric will have the minimum MPS set. If the PCI hotplug
> + * slot is directly connected to the root port and there are not
> + * other devices on the fabric (which seems to be the most
> + * common case), then this is not an issue and MPS discovery
> + * will occur as normal.
> + */
> + if (dev->is_hotplug_bridge && (!list_is_singular(&dev->bus->devices) ||
> + dev->bus->self->pcie_type != PCI_EXP_TYPE_ROOT_PORT))
> + *smpss = 0;
> +
> + if (*smpss > dev->pcie_mpss)
> + *smpss = dev->pcie_mpss;
> +
> + return 0;
> +}
> +
> +static void pcie_write_mps(struct pci_dev *dev, int mps)
> +{
> + int rc, dev_mpss;
> +
> + dev_mpss = 128 << dev->pcie_mpss;
> +
> + if (pcie_bus_config == PCIE_BUS_PERFORMANCE) {
> + if (dev->bus->self) {
> + dev_dbg(&dev->bus->dev, "Bus MPSS %d\n",
> + 128 << dev->bus->self->pcie_mpss);
> +
> + /* For "MPS Force Max", the assumption is made that
> + * downstream communication will never be larger than
> + * the MRRS. So, the MPS only needs to be configured
> + * for the upstream communication. This being the case,
> + * walk from the top down and set the MPS of the child
> + * to that of the parent bus.
> + */
> + mps = 128 << dev->bus->self->pcie_mpss;
> + if (mps > dev_mpss)
> + dev_warn(&dev->dev, "MPS configured higher than"
> + " maximum supported by the device. If"
> + " a bus issue occurs, try running with"
> + " pci=pcie_bus_safe.\n");
> + }
> +
> + dev->pcie_mpss = ffs(mps) - 8;
> + }
> +
> + rc = pcie_set_mps(dev, mps);
> + if (rc)
> + dev_err(&dev->dev, "Failed attempting to set the MPS\n");
> +}
> +
> +static void pcie_write_mrrs(struct pci_dev *dev, int mps)
> +{
> + int rc, mrrs;
> +
> + if (pcie_bus_config == PCIE_BUS_PERFORMANCE) {
> + int dev_mpss = 128 << dev->pcie_mpss;
> +
> + /* For Max performance, the MRRS must be set to the largest
> + * supported value. However, it cannot be configured larger
> + * than the MPS the device or the bus can support. This assumes
> + * that the largest MRRS available on the device cannot be
> + * smaller than the device MPSS.
> + */
> + mrrs = mps < dev_mpss ? mps : dev_mpss;
> + } else
> + /* In the "safe" case, configure the MRRS for fairness on the
> + * bus by making all devices have the same size
> + */
> + mrrs = mps;
> +
> +
> + /* MRRS is a R/W register. Invalid values can be written, but a
> + * subsiquent read will verify if the value is acceptable or not.
> + * If the MRRS value provided is not acceptable (e.g., too large),
> + * shrink the value until it is acceptable to the HW.
> + */
> + while (mrrs != pcie_get_readrq(dev) && mrrs >= 128) {
> + rc = pcie_set_readrq(dev, mrrs);
> + if (rc)
> + dev_err(&dev->dev, "Failed attempting to set the MRRS\n");
> +
> + mrrs /= 2;
> + }
> +}
> +
> +static int pcie_bus_configure_set(struct pci_dev *dev, void *data)
> +{
> + int mps = 128 << *(u8 *)data;
> +
> + if (!pci_is_pcie(dev))
> + return 0;
> +
> + dev_info(&dev->dev, "Dev MPS %d MPSS %d MRRS %d\n",
> + pcie_get_mps(dev), 128<<dev->pcie_mpss, pcie_get_readrq(dev));
> +
> + pcie_write_mps(dev, mps);
> + pcie_write_mrrs(dev, mps);
> +
> + dev_info(&dev->dev, "Dev MPS %d MPSS %d MRRS %d\n",
> + pcie_get_mps(dev), 128<<dev->pcie_mpss, pcie_get_readrq(dev));
> +
> + return 0;
> +}
> +
> +/* pcie_bus_configure_mps requires that pci_walk_bus work in a top-down,
> + * parents then children fashion. If this changes, then this code will not
> + * work as designed.
> + */
> +void pcie_bus_configure_settings(struct pci_bus *bus, u8 mpss)
> +{
> + u8 smpss = mpss;
> +
> + if (!bus->self)
> + return;
> +
> + if (!pci_is_pcie(bus->self))
> + return;
> +
> + if (pcie_bus_config == PCIE_BUS_SAFE) {
> + pcie_find_smpss(bus->self, &smpss);
> + pci_walk_bus(bus, pcie_find_smpss, &smpss);
> + }
> +
> + pcie_bus_configure_set(bus->self, &smpss);
> + pci_walk_bus(bus, pcie_bus_configure_set, &smpss);
> +}
> +
> unsigned int __devinit pci_scan_child_bus(struct pci_bus *bus)
> {
> unsigned int devfn, pass, max = bus->secondary;
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -251,7 +251,8 @@ struct pci_dev {
> u8 revision; /* PCI revision, low byte of class word */
> u8 hdr_type; /* PCI header type (`multi' flag masked out) */
> u8 pcie_cap; /* PCI-E capability offset */
> - u8 pcie_type; /* PCI-E device/port type */
> + u8 pcie_type:4; /* PCI-E device/port type */
> + u8 pcie_mpss:3; /* PCI-E Max Payload Size Supported */
> u8 rom_base_reg; /* which config register controls the ROM */
> u8 pin; /* which interrupt pin this device uses */
>
> @@ -617,6 +618,16 @@ struct pci_driver {
> /* these external functions are only available when PCI support is enabled */
> #ifdef CONFIG_PCI
>
> +extern void pcie_bus_configure_settings(struct pci_bus *bus, u8 smpss);
> +
> +enum pcie_bus_config_types {
> + PCIE_BUS_PERFORMANCE,
> + PCIE_BUS_SAFE,
> + PCIE_BUS_PEER2PEER,
> +};
> +
> +extern enum pcie_bus_config_types pcie_bus_config;
> +
> extern struct bus_type pci_bus_type;
>
> /* Do NOT directly access these two variables, unless you are arch specific pci
> @@ -796,6 +807,8 @@ int pcix_get_mmrbc(struct pci_dev *dev);
> int pcix_set_mmrbc(struct pci_dev *dev, int mmrbc);
> int pcie_get_readrq(struct pci_dev *dev);
> int pcie_set_readrq(struct pci_dev *dev, int rq);
> +int pcie_get_mps(struct pci_dev *dev);
> +int pcie_set_mps(struct pci_dev *dev, int mps);
> int __pci_reset_function(struct pci_dev *dev);
> int pci_reset_function(struct pci_dev *dev);
> void pci_update_resource(struct pci_dev *dev, int resno);
>
>
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