Re: [PATCH] Documentation: media: improve V4L2_CID_MIN_BUFFERS_FOR_*, doc

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Thu, Oct 31, 2024 at 11:26:47AM +0100, Hans Verkuil wrote:
> On 10/31/24 11:11, Laurent Pinchart wrote:
> > Hi Hans,
> > 
> > Thank you for the patch.
> > 
> > On Thu, Oct 31, 2024 at 08:50:04AM +0100, Hans Verkuil wrote:
> >> Clearly state that the V4L2_CID_MIN_BUFFERS_FOR_OUTPUT and
> >> V4L2_CID_MIN_BUFFERS_FOR_CAPTURE controls are required for
> >> stateful codecs.
> > 
> > Wouldn't it be better for this kind of information to be centralized in
> > a stateful decoder document ? That would make it easier for developers
> > to see all they need to implement. Otherwise they would need to read
> > through the whole documentation to pick the parts of the API they need
> > to support in their drivers.
> 
> It's also already mentioned in the documentation for the stateful de/encoders here:
> 
> https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/dev-mem2mem.html

OK, then it's fine to have it here too I think.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> Also, once this vicodec patch is merged:
> 
> https://patchwork.linuxtv.org/project/linux-media/patch/1dd09050-40ca-4c5b-b985-819731140388@xs4all.nl/
> 
> I plan to push v4l2-compliance patches that explicitly test for the presence of
> these controls and fail if they are missing (like they are now in vicodec).
>
> >> Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
> >> ---
> >>  Documentation/userspace-api/media/v4l/control.rst | 6 ++++--
> >>  1 file changed, 4 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/Documentation/userspace-api/media/v4l/control.rst b/Documentation/userspace-api/media/v4l/control.rst
> >> index 57893814a1e5..9253cc946f02 100644
> >> --- a/Documentation/userspace-api/media/v4l/control.rst
> >> +++ b/Documentation/userspace-api/media/v4l/control.rst
> >> @@ -290,13 +290,15 @@ Control IDs
> >>      This is a read-only control that can be read by the application and
> >>      used as a hint to determine the number of CAPTURE buffers to pass to
> >>      REQBUFS. The value is the minimum number of CAPTURE buffers that is
> >> -    necessary for hardware to work.
> >> +    necessary for hardware to work. This control is required for stateful
> >> +    decoders.
> >>
> >>  ``V4L2_CID_MIN_BUFFERS_FOR_OUTPUT`` ``(integer)``
> >>      This is a read-only control that can be read by the application and
> >>      used as a hint to determine the number of OUTPUT buffers to pass to
> >>      REQBUFS. The value is the minimum number of OUTPUT buffers that is
> >> -    necessary for hardware to work.
> >> +    necessary for hardware to work. This control is required for stateful
> >> +    encoders.
> >>
> >>  .. _v4l2-alpha-component:
> >>

-- 
Regards,

Laurent Pinchart