On Fri, 2019-04-05 at 13:21 +0200, Hans Verkuil 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. > > > > > 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. v4l2-compliance currently complains if V4L2_DEC_CMD_STOP_IMMEDIATELY is not supported: fail: v4l2-test-codecs.cpp(104): ret != 0 test VIDIOC_(TRY_)DECODER_CMD: FAIL Should testDecoder be changed to set the V4L2_DEC_CMD_STOP_IMMEDIATELY flag only if node->codec_mask does not have the STATEFUL_DECODER bit set? regards Philipp
