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authorLinus Torvalds <torvalds@linux-foundation.org>2012-04-04 17:13:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-04-04 17:13:43 -0700
commit58bca4a8fa90fcf9069379653b396b2cec642f7f (patch)
tree483c535136b5b168f36326956453e80ce5aa6543 /Documentation
parent64ebe987311853ea857a244439de5b947a4b1b07 (diff)
parent64d70fe5d3640e1a89790ed21120921278f8cb86 (diff)
Merge branch 'for-linus' of git://git.linaro.org/people/mszyprowski/linux-dma-mapping
Pull DMA mapping branch from Marek Szyprowski: "Short summary for the whole series: A few limitations have been identified in the current dma-mapping design and its implementations for various architectures. There exist more than one function for allocating and freeing the buffers: currently these 3 are used dma_{alloc, free}_coherent, dma_{alloc,free}_writecombine, dma_{alloc,free}_noncoherent. For most of the systems these calls are almost equivalent and can be interchanged. For others, especially the truly non-coherent ones (like ARM), the difference can be easily noticed in overall driver performance. Sadly not all architectures provide implementations for all of them, so the drivers might need to be adapted and cannot be easily shared between different architectures. The provided patches unify all these functions and hide the differences under the already existing dma attributes concept. The thread with more references is available here: http://www.spinics.net/lists/linux-sh/msg09777.html These patches are also a prerequisite for unifying DMA-mapping implementation on ARM architecture with the common one provided by dma_map_ops structure and extending it with IOMMU support. More information is available in the following thread: http://thread.gmane.org/gmane.linux.kernel.cross-arch/12819 More works on dma-mapping framework are planned, especially in the area of buffer sharing and managing the shared mappings (together with the recently introduced dma_buf interface: commit d15bd7ee445d "dma-buf: Introduce dma buffer sharing mechanism"). The patches in the current set introduce a new alloc/free methods (with support for memory attributes) in dma_map_ops structure, which will later replace dma_alloc_coherent and dma_alloc_writecombine functions." People finally started piping up with support for merging this, so I'm merging it as the last of the pending stuff from the merge window. Looks like pohmelfs is going to wait for 3.5 and more external support for merging. * 'for-linus' of git://git.linaro.org/people/mszyprowski/linux-dma-mapping: common: DMA-mapping: add NON-CONSISTENT attribute common: DMA-mapping: add WRITE_COMBINE attribute common: dma-mapping: introduce mmap method common: dma-mapping: remove old alloc_coherent and free_coherent methods Hexagon: adapt for dma_map_ops changes Unicore32: adapt for dma_map_ops changes Microblaze: adapt for dma_map_ops changes SH: adapt for dma_map_ops changes Alpha: adapt for dma_map_ops changes SPARC: adapt for dma_map_ops changes PowerPC: adapt for dma_map_ops changes MIPS: adapt for dma_map_ops changes X86 & IA64: adapt for dma_map_ops changes common: dma-mapping: introduce generic alloc() and free() methods
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/DMA-attributes.txt18
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index b768cc0e402b..5c72eed89563 100644
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -31,3 +31,21 @@ may be weakly ordered, that is that reads and writes may pass each other.
Since it is optional for platforms to implement DMA_ATTR_WEAK_ORDERING,
those that do not will simply ignore the attribute and exhibit default
behavior.
+
+DMA_ATTR_WRITE_COMBINE
+----------------------
+
+DMA_ATTR_WRITE_COMBINE specifies that writes to the mapping may be
+buffered to improve performance.
+
+Since it is optional for platforms to implement DMA_ATTR_WRITE_COMBINE,
+those that do not will simply ignore the attribute and exhibit default
+behavior.
+
+DMA_ATTR_NON_CONSISTENT
+-----------------------
+
+DMA_ATTR_NON_CONSISTENT lets the platform to choose to return either
+consistent or non-consistent memory as it sees fit. By using this API,
+you are guaranteeing to the platform that you have all the correct and
+necessary sync points for this memory in the driver.