On 07/24/2018 04:06 PM, 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 | 872 +++++++++++++++++++ > Documentation/media/uapi/v4l/devices.rst | 1 + > Documentation/media/uapi/v4l/v4l2.rst | 10 +- > 3 files changed, 882 insertions(+), 1 deletion(-) > 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..f55d34d2f860 > --- /dev/null > +++ b/Documentation/media/uapi/v4l/dev-decoder.rst > @@ -0,0 +1,872 @@ <snip> > +6. 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 driver must keep processing and returning > + each buffer to the client until required metadata to configure the > + ``CAPTURE`` queue are found. This is indicated by the driver sending > + a ``V4L2_EVENT_SOURCE_CHANGE`` event with > + ``V4L2_EVENT_SRC_CH_RESOLUTION`` source change type. There is no > + requirement to pass enough data for this to occur in the first buffer > + and the driver must be able to process any number. > + > + * If data in a buffer that triggers the event is required to decode > + the first frame, the driver must not return it to the client, > + but must retain it for further decoding. > + > + * If the client set width and height of ``OUTPUT`` format to 0, calling > + :c:func:`VIDIOC_G_FMT` on the ``CAPTURE`` queue will return -EPERM, > + until the driver configures ``CAPTURE`` format according to stream > + metadata. What about calling TRY/S_FMT on the capture queue: will this also return -EPERM? I assume so. Regards, Hans
