On Thu, 2019-01-31 at 13:30 +0100, Hans Verkuil wrote: > On 1/31/19 11:45 AM, Hans Verkuil wrote: > > On 1/24/19 11:04 AM, 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 > > > > > > > <snip> > > > > > +4. **This step only applies to coded formats that contain resolution information > > > + in the stream.** Continue queuing/dequeuing bitstream buffers to/from the > > > + ``OUTPUT`` queue via :c:func:`VIDIOC_QBUF` and :c:func:`VIDIOC_DQBUF`. The > > > + buffers will be processed and returned to the client in order, until > > > + required metadata to configure the ``CAPTURE`` queue are found. This is > > > + indicated by the decoder sending a ``V4L2_EVENT_SOURCE_CHANGE`` event with > > > + ``V4L2_EVENT_SRC_CH_RESOLUTION`` source change type. > > > + > > > + * It is not an error if the first buffer does not contain enough data for > > > + this to occur. Processing of the buffers will continue as long as more > > > + data is needed. > > > + > > > + * If data in a buffer that triggers the event is required to decode the > > > + first frame, it will not be returned to the client, until the > > > + initialization sequence completes and the frame is decoded. > > > + > > > + * If the client sets width and height of the ``OUTPUT`` format to 0, > > > + calling :c:func:`VIDIOC_G_FMT`, :c:func:`VIDIOC_S_FMT`, > > > + :c:func:`VIDIOC_TRY_FMT` or :c:func:`VIDIOC_REQBUFS` on the ``CAPTURE`` > > > + queue will return the ``-EACCES`` error code, until the decoder > > > + configures ``CAPTURE`` format according to stream metadata. > > > > I think this should also include the G/S_SELECTION ioctls, right? > > I've started work on adding compliance tests for codecs to v4l2-compliance and > I quickly discovered that this 'EACCES' error code is not nice at all. > > The problem is that it is really inconsistent with V4L2 behavior: the basic > rule is that there always is a format defined, i.e. G_FMT will always return > a format. > > Suddenly returning an error is actually quite painful to handle because it is > a weird exception just for the capture queue of a stateful decoder if no > output resolution is known. > > Just writing that sentence is painful. > > Why not just return some default driver defined format? It will automatically > be updated once the decoder parsed the bitstream and knows the new resolution. > > It really is just the same behavior as with a resolution change. > > It is also perfectly fine to request buffers for the capture queue for that > default format. It's pointless, but not a bug. > > Unless I am missing something I strongly recommend changing this behavior. I just wrote the same in my reply to Nicolas, the CODA driver currently sets the capture queue width/height to the output queue's crop rectangle (rounded to macroblock size) without ever having seen the SPS. regards Philipp
