Commit 2fd74e25 authored by FUJITA Tomonori's avatar FUJITA Tomonori Committed by Linus Torvalds
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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: default avatarFUJITA Tomonori <>
Cc: "David S. Miller" <>
Cc: Matt Mackall <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 4ae9ca82
......@@ -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
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