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>
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 @@
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