[PATCH -mm] Documentation/DMA-API-HOWTO: add ARCH_KMALLOC_MINALIGNdescription

From: FUJITA Tomonori
Date: Fri May 21 2010 - 20:38:15 EST

Adds ARCH_KMALLOC_MINALIGN description in "Platform Issues" section.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>
Documentation/DMA-API-HOWTO.txt | 15 ++++++++++++++-
1 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt
index bfd94e9..98ce517 100644
--- a/Documentation/DMA-API-HOWTO.txt
+++ b/Documentation/DMA-API-HOWTO.txt
@@ -738,7 +738,20 @@ to "Closing".
CONFIG_NEED_SG_DMA_LENGTH if the architecture supports IOMMUs
(including software IOMMU).

-2) More to come...
+ 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_KMALLOC_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_KMALLOC_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).



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