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common: DMA-mapping: add DMA_ATTR_NO_KERNEL_MAPPING attribute 

This patch adds DMA_ATTR_NO_KERNEL_MAPPING attribute which 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().

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
hifive-unleashed-5.1
Marek Szyprowski 2012-05-16 15:20:37 +02:00
parent 64ccc9c033
commit d5724f172f
2 changed files with 19 additions and 0 deletions
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18
Documentation/DMA-attributes.txt
View File

@ -49,3 +49,21 @@ 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.

1
include/linux/dma-attrs.h
View File

@ -15,6 +15,7 @@ enum dma_attr {
DMA_ATTR_WEAK_ORDERING,
DMA_ATTR_WRITE_COMBINE,
DMA_ATTR_NON_CONSISTENT,
DMA_ATTR_NO_KERNEL_MAPPING,
DMA_ATTR_MAX,
};