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. > >> + 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. Regards, Hans > > regards > Philipp >
