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Commit cc36e64a authored Oct 29, 2012 by Laura Abbott Committed by Patrick Daly Aug 24, 2016

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>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>

parent 0727443a

Documentation/DMA-attributes.txt

+9 −0

Original line number	Diff line number	Diff line
		@@ -126,3 +126,12 @@ means that we won't try quite as hard to get them.

		NOTE: At the moment DMA_ATTR_ALLOC_SINGLE_PAGES is only implemented on ARM,
		though ARM64 patches will likely be posted soon.

		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.

include/linux/dma-mapping.h

+6 −0

Original line number	Diff line number	Diff line
		@@ -56,6 +56,12 @@
		* that gives better TLB efficiency.
		*/
		#define DMA_ATTR_ALLOC_SINGLE_PAGES (1UL << 7)
		/*
		* DMA_ATTR_STRONGLY_ORDERED: Specifies that accesses to the mapping must
		* not be buffered, reordered, merged with other accesses, or unaligned.
		* No speculative access may occur in this mapping.
		*/
		#define DMA_ATTR_STRONGLY_ORDERED (1UL << 8)

		/*
		* A dma_addr_t can hold any valid DMA or bus address for the platform.