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common: DMA-mapping: Add strongly ordered memory attribute

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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>
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
This commit is contained in:
Laura Abbott
2012-10-29 13:08:03 -07:00
committed by Stephen Boyd
parent 0f53e5abb2
commit c1386f095a
2 changed files with 10 additions and 0 deletions
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9
Documentation/DMA-attributes.txt
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@@ -67,3 +67,12 @@ set on each call.
Since it is optional for platforms to implement Since it is optional for platforms to implement
DMA_ATTR_NO_KERNEL_MAPPING, those that do not will simply ignore the DMA_ATTR_NO_KERNEL_MAPPING, those that do not will simply ignore the
attribute and exhibit default behavior. attribute and exhibit default behavior.
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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@@ -16,6 +16,7 @@ enum dma_attr {
DMA_ATTR_WRITE_COMBINE, DMA_ATTR_WRITE_COMBINE,
DMA_ATTR_NON_CONSISTENT, DMA_ATTR_NON_CONSISTENT,
DMA_ATTR_NO_KERNEL_MAPPING, DMA_ATTR_NO_KERNEL_MAPPING,
DMA_ATTR_STRONGLY_ORDERED,
DMA_ATTR_MAX, DMA_ATTR_MAX,
}; };