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authorLinus Torvalds <torvalds@linux-foundation.org>2012-07-30 10:11:31 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-07-30 10:11:31 -0700
commit6f51f51582e793ea13e7de7ed6b138f71c51784b (patch)
tree211ecbf88cdf2f183e23da3f8f23153ac6133410 /Documentation
parent76159c20c0bcf5b38178fbfb61049eeb6380bb54 (diff)
parent97ef952a20853fad72087a53fa556fbec45edd8f (diff)
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Merge branch 'for-linus-for-3.6-rc1' of git://git.linaro.org/people/mszyprowski/linux-dma-mapping
Pull DMA-mapping updates from Marek Szyprowski: "Those patches are continuation of my earlier work. They contains extensions to DMA-mapping framework to remove limitation of the current ARM implementation (like limited total size of DMA coherent/write combine buffers), improve performance of buffer sharing between devices (attributes to skip cpu cache operations or creation of additional kernel mapping for some specific use cases) as well as some unification of the common code for dma_mmap_attrs() and dma_mmap_coherent() functions. All extensions have been implemented and tested for ARM architecture." * 'for-linus-for-3.6-rc1' of git://git.linaro.org/people/mszyprowski/linux-dma-mapping: ARM: dma-mapping: add support for DMA_ATTR_SKIP_CPU_SYNC attribute common: DMA-mapping: add DMA_ATTR_SKIP_CPU_SYNC attribute ARM: dma-mapping: add support for dma_get_sgtable() common: dma-mapping: introduce dma_get_sgtable() function ARM: dma-mapping: add support for DMA_ATTR_NO_KERNEL_MAPPING attribute common: DMA-mapping: add DMA_ATTR_NO_KERNEL_MAPPING attribute common: dma-mapping: add support for generic dma_mmap_* calls ARM: dma-mapping: fix error path for memory allocation failure ARM: dma-mapping: add more sanity checks in arm_dma_mmap() ARM: dma-mapping: remove custom consistent dma region mm: vmalloc: use const void * for caller argument scatterlist: add sg_alloc_table_from_pages function
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/DMA-attributes.txt42
-rw-r--r--Documentation/kernel-parameters.txt2
2 files changed, 43 insertions, 1 deletions
diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index 5c72eed8956..f50309081ac 100644
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -49,3 +49,45 @@ 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.
+
+DMA_ATTR_NO_KERNEL_MAPPING
+--------------------------
+
+DMA_ATTR_NO_KERNEL_MAPPING lets the platform to avoid creating a kernel
+virtual mapping for the allocated buffer. On some architectures creating
+such mapping is non-trivial task and consumes very limited resources
+(like kernel virtual address space or dma consistent address space).
+Buffers allocated with this attribute can be only passed to user space
+by calling dma_mmap_attrs(). By using this API, you are guaranteeing
+that you won't dereference the pointer returned by dma_alloc_attr(). You
+can threat it as a cookie that must be passed to dma_mmap_attrs() and
+dma_free_attrs(). Make sure that both of these also get this attribute
+set on each call.
+
+Since it is optional for platforms to implement
+DMA_ATTR_NO_KERNEL_MAPPING, those that do not will simply ignore the
+attribute and exhibit default behavior.
+
+DMA_ATTR_SKIP_CPU_SYNC
+----------------------
+
+By default dma_map_{single,page,sg} functions family transfer a given
+buffer from CPU domain to device domain. Some advanced use cases might
+require sharing a buffer between more than one device. This requires
+having a mapping created separately for each device and is usually
+performed by calling dma_map_{single,page,sg} function more than once
+for the given buffer with device pointer to each device taking part in
+the buffer sharing. The first call transfers a buffer from 'CPU' domain
+to 'device' domain, what synchronizes CPU caches for the given region
+(usually it means that the cache has been flushed or invalidated
+depending on the dma direction). However, next calls to
+dma_map_{single,page,sg}() for other devices will perform exactly the
+same sychronization operation on the CPU cache. CPU cache sychronization
+might be a time consuming operation, especially if the buffers are
+large, so it is highly recommended to avoid it if possible.
+DMA_ATTR_SKIP_CPU_SYNC allows platform code to skip synchronization of
+the CPU cache for the given buffer assuming that it has been already
+transferred to 'device' domain. This attribute can be also used for
+dma_unmap_{single,page,sg} functions family to force buffer to stay in
+device domain after releasing a mapping for it. Use this attribute with
+care!
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c2619ef44a7..ad7e2e5088c 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -526,7 +526,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
coherent_pool=nn[KMG] [ARM,KNL]
Sets the size of memory pool for coherent, atomic dma
- allocations if Contiguous Memory Allocator (CMA) is used.
+ allocations, by default set to 256K.
code_bytes [X86] How many bytes of object code to print
in an oops report.