On Fri, Apr 5, 2019 at 8:21 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote: > > On 4/5/19 12:59 PM, Philipp Zabel wrote: > > On Thu, 2019-01-24 at 19:04 +0900, Tomasz Figa wrote: > >> Due to complexity of the video decoding process, the V4L2 drivers of > >> stateful decoder hardware require specific sequences of V4L2 API calls > >> to be followed. These include capability enumeration, initialization, > >> decoding, seek, pause, dynamic resolution change, drain and end of > >> stream. > >> > >> Specifics of the above have been discussed during Media Workshops at > >> LinuxCon Europe 2012 in Barcelona and then later Embedded Linux > >> Conference Europe 2014 in Düsseldorf. The de facto Codec API that > >> originated at those events was later implemented by the drivers we already > >> have merged in mainline, such as s5p-mfc or coda. > >> > >> The only thing missing was the real specification included as a part of > >> Linux Media documentation. Fix it now and document the decoder part of > >> the Codec API. > >> > >> Signed-off-by: Tomasz Figa <tfiga@xxxxxxxxxxxx> > >> --- > >> Documentation/media/uapi/v4l/dev-decoder.rst | 1076 +++++++++++++++++ > >> Documentation/media/uapi/v4l/dev-mem2mem.rst | 5 + > >> Documentation/media/uapi/v4l/pixfmt-v4l2.rst | 5 + > >> Documentation/media/uapi/v4l/v4l2.rst | 10 +- > >> .../media/uapi/v4l/vidioc-decoder-cmd.rst | 40 +- > >> Documentation/media/uapi/v4l/vidioc-g-fmt.rst | 14 + > >> 6 files changed, 1135 insertions(+), 15 deletions(-) > >> create mode 100644 Documentation/media/uapi/v4l/dev-decoder.rst > >> > >> diff --git a/Documentation/media/uapi/v4l/dev-decoder.rst b/Documentation/media/uapi/v4l/dev-decoder.rst > >> new file mode 100644 > >> index 000000000000..b7db2352ad41 > >> --- /dev/null > >> +++ b/Documentation/media/uapi/v4l/dev-decoder.rst > >> @@ -0,0 +1,1076 @@ > >> +.. -*- coding: utf-8; mode: rst -*- > >> + > >> +.. _decoder: > >> + > >> +************************************************* > >> +Memory-to-memory Stateful Video Decoder Interface > >> +************************************************* > >> + > > [...] > >> + > >> +Drain > >> +===== > >> + > > [...] > >> + > >> +3. Once all the ``OUTPUT`` buffers queued before the ``V4L2_DEC_CMD_STOP`` call > >> + are dequeued and the last ``CAPTURE`` buffer is dequeued, the decoder is > >> + stopped and it will accept, but not process, any newly queued ``OUTPUT`` > >> + buffers until the client issues any of the following operations: > >> + > > [...] > >> + > >> +.. note:: > >> + > >> + Once the drain sequence is initiated, the client needs to drive it to > >> + completion, as described by the steps above, unless it aborts the process by > >> + issuing :c:func:`VIDIOC_STREAMOFF` on any of the ``OUTPUT`` or ``CAPTURE`` > >> + queues. The client is not allowed to issue ``V4L2_DEC_CMD_START`` or > >> + ``V4L2_DEC_CMD_STOP`` again while the drain sequence is in progress and they > >> + will fail with -EBUSY error code if attempted. > > > > Should the V4L2_DEC_CMD_STOP documentation in > > Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst: > > > > * - ``V4L2_DEC_CMD_STOP`` > > - 1 > > - Stop the decoder. When the decoder is already stopped, this > > command does nothing. > > > > be updated to mention that for mem2mem decoders this not only does > > nothing, but returns an -EBUSY error return value? > > Yes. Basically in this case the STOP is still in progress, so returning > EBUSY makes sense and should be documented. > Done. Also for the encoder. > > > > Also, if V4L2_DEC_CMD_STOP_IMMEDIATELY is set, should the decoder drop > > all pending buffers and signal EOS immediately? Should this be mentioned > > here? > > Hmm, the decoder spec says that flags should be set to 0, and current codec > drivers explicitly disallow a non-0 flags value. > > I'm not sure if there is a practical use-case for V4L2_DEC_CMD_STOP_IMMEDIATELY > in the context of a decoder. If you want to stop immediately, then just call > streamoff on the OUTPUT queue. > Agreed. > > > >> + Although mandatory, the availability of decoder commands may be queried > >> + using :c:func:`VIDIOC_TRY_DECODER_CMD`. > > > > Do the TRY_DECODER_CMD also return -EBUSY during the draining phase? > > No. Ack. Best regards, Tomasz > > Regards, > > Hans > > > > > regards > > Philipp > > >
