[Linaro-mm-sig] [RFC v2] dma-buf: Add buffer sharing framework
sumit.semwal at linaro.org
Wed Sep 28 05:17:11 UTC 2011
Hi Hans, Daniel, Rob,
On 28 September 2011 04:07, Clark, Rob <rob at ti.com> wrote:
> On Tue, Sep 27, 2011 at 9:19 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> >> One other thing: once you call REQBUFS on a V4L device the V4L spec says
> >> 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.
Thanks and best regards,
Linaro Kernel Engineer - Graphics working group
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