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Documentation/DMA-API-HOWTO: add ARCH_KMALLOC_MINALIGN description 

Add ARCH_KMALLOC_MINALIGN description in "Platform Issues" section.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
FUJITA Tomonori 2010-05-26 14:44:23 -07:00 committed by Linus Torvalds
parent 4ae9ca825e
commit 2fd74e25df
1 changed files with 14 additions and 1 deletions
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15
Documentation/DMA-API-HOWTO.txt
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@ -738,7 +738,20 @@ to "Closing".
CONFIG_NEED_SG_DMA_LENGTH if the architecture supports IOMMUs
(including software IOMMU).
2) More to come...
2) ARCH_KMALLOC_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_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).
Closing