[Linaro-mm-sig] [RFC v2] dma-buf: Add buffer sharing framework

[Clark, Rob]

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 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.

BR,
-R