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common: DMA-mapping: Add strongly ordered memory attribute 

Strongly ordered memory is occasionally needed for some DMA
allocations for specialized use cases. Add the corresponding
DMA attribute.

Change-Id: Idd9e756c242ef57d6fa6700e51cc38d0863b760d
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
This commit is contained in:
Laura Abbott 2012-10-29 13:08:03 -07:00 committed by Stephen Boyd
parent ead31d5027
commit 12423d3e4f
2 changed files with 10 additions and 0 deletions
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9
Documentation/DMA-attributes.txt
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@ -100,3 +100,12 @@ allocated by dma_alloc_attrs() function from individual pages if it can
be mapped as contiguous chunk into device dma address space. By
specifing this attribute the allocated buffer is forced to be contiguous
also in physical memory.
DMA_ATTR_STRONGLY_ORDERED
-------------------------
DMA_ATTR_STRONGLY_ORDERED allocates memory with a very restrictive type
of mapping (no unaligned accesses, no re-ordering, no write merging, no
buffering, no pre-fetching). This has severe performance penalties and
should not be used for general purpose DMA allocations. It should only
be used if one of the restrictions on strongly ordered memory is required.

1
include/linux/dma-attrs.h
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@ -18,6 +18,7 @@ enum dma_attr {
DMA_ATTR_NO_KERNEL_MAPPING,
DMA_ATTR_SKIP_CPU_SYNC,
DMA_ATTR_FORCE_CONTIGUOUS,
DMA_ATTR_STRONGLY_ORDERED,
DMA_ATTR_MAX,
};