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dma-buf: add initial vmap documentation 

Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
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Dave Airlie 2012-05-22 13:34:38 +01:00 committed by Sumit Semwal
parent 12c4727e1d
commit b25b086d23
1 changed files with 11 additions and 0 deletions
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Documentation/dma-buf-sharing.txt
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@ -293,6 +293,17 @@ Access to a dma_buf from the kernel context involves three steps:
Note that these calls need to always succeed. The exporter needs to complete Note that these calls need to always succeed. The exporter needs to complete
any preparations that might fail in begin_cpu_access. any preparations that might fail in begin_cpu_access.
For some cases the overhead of kmap can be too high, a vmap interface
is introduced. This interface should be used very carefully, as vmalloc
space is a limited resources on many architectures.
Interfaces:
void *dma_buf_vmap(struct dma_buf *dmabuf)
void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
The vmap call can fail if there is no vmap support in the exporter, or if it
runs out of vmalloc space. Fallback to kmap should be implemented.
3. Finish access 3. Finish access
When the importer is done accessing the range specified in begin_cpu_access, When the importer is done accessing the range specified in begin_cpu_access,