Hi Hans, Daniel, Rob,
On 28 September 2011 04:07, Clark, Rob rob@ti.com wrote:
On Tue, Sep 27, 2011 at 9:19 AM, Daniel Vetter daniel@ffwll.ch wrote:
One other thing: once you call REQBUFS on a V4L device the V4L spec says
that
the memory should be allocated at that time. Because V4L often needs a
lot of
memory that behavior makes sense: you know immediately if you can get
the memory
or not. In addition, that memory is mmap-ed before the DMA is started.
If that is actually a fixed requirement for v4l, that's a good reason for mmap support on the dma_buf object. We could hide all the complecity of shooting down userspace mmapings on buffer movements from the drivers. Can you elaborate a bit on this?
I would hope if we are using V4L2_MEMORY_DMABUF that V4L should not create a user mapping of the buffer.
Given that V4L2_MEMORY_DMABUF is something new, I think it is fine to spec out this part of the V4L spec to now require a userspace mapping.
Thanks for your questions and comments - and for clarifying the use cases to Hans. I will create a Documentation doc for explaining it as easily and crisply as Daniel has done. I will also update the patch based on all your comments - I think a v3 posted here is warranted before I post to upstream lists I guess.
BR, -R
Thanks and best regards,
Sumit Semwal
Linaro Kernel Engineer - Graphics working group
Linaro.org http://www.linaro.org/* **│ *Open source software for ARM SoCs* ***
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