RE: [PATCH v2 1/2] v4l: Add resolution change event.

[Kamil Debski <k.debski@samsung.com>]

Hi Pawel,

> From: Pawel Osciak [mailto:posciak@chromium.org]
> Sent: Monday, April 21, 2014 12:27 PM
> To: Arun Kumar K
> Cc: linux-media@vger.kernel.org; linux-samsung-soc; Kamil Debski;
> Sylwester Nawrocki; Hans Verkuil; Laurent Pinchart
> Subject: Re: [PATCH v2 1/2] v4l: Add resolution change event.
> 
> As a side note, because this is not really codified in the API, I would
> like this event to indicate not only resolution change mid-stream, but
> also detection of initial resolution, which should be a subset of
> resolution change. I think this would make sense for the codec
> interface:
> 
> Video decode:
> 1. S_FMT to given codec on OUTPUT queue.
> 2. REQBUFS(n) and STREAMON on OUTPUT queue.
> 3. Keep QBUFing until we get an resolution change event on the CAPTURE
> queue; until then, the driver/codec HW will operate on the OUTPUT queue
> only and try to detect relevant headers in the OUTPUT buffers, and will
> send resolution change event once it finds resolution, profile, etc.
> info). DQEVENT.
> 4. G_FMT on CAPTURE to get the discovered output format (resolution),
> REQBUFS and STREAMON on the CAPTURE queue.
> 5. Normal mem-to-mem decoding.
> 6. If a resolution change event arrives on CAPTURE queue, DQEVENT,
> STREAMOFF, REQBUFS(0) only on CAPTURE queue, and goto 4. OUTPUT queue
> operates completely independently of this.
> 
> Also, this event should invariably indicate all of the below:
> - all output buffers from before resolution change are already ready on
> the CAPTURE queue to DQBUF (so it's ready to REQBUFS(0) after DQBUFs),
> and
> - there will be no more new ready buffers on the CAPTURE queue until
> the streamoff-reqbufs(0)-g_fmt-reqbufs()-streamon is performed, and
> - OUTPUT queue is completely independent of all of the above and can be
> still used as normal, i.e. stream buffers can still keep being queued
> at any stage of the resolution change and they will be decoded after
> resolution change sequence is finished;
> 
> If we all agree to the above, I will prepare a subsequent patch for the
> documentation to include the above.

If I understand correctly this will keep the old application working.
By this I mean application that do not use events and rely on the current
mechanism to detect initial header parsing and resolution change.

If backward compatibility is kept I am all for the changes proposed by you.

> 
> Thanks,
> Pawel

Best wishes,
-- 
Kamil Debski
Samsung R&D Institute Poland