On 4/9/19 6:57 PM, Philipp Zabel wrote: > 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? Yes. I see that the vicodec driver doesn't handle the DECODER_CMD ioctl correctly, which is why I haven't noticed this v4l2-compliance issue before. Regards, Hans > > regards > Philipp >
