Re: [PATCH v2 1/2] media: docs-rst: Document memory-to-memory video decoder interface

[Stanimir Varbanov]

Hi Tomasz,

On 10/22/2018 05:48 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 DÃsseldorf. 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  | 1082 +++++++++++++++++
>  Documentation/media/uapi/v4l/devices.rst      |    1 +
>  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, 1137 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..09c7a6621b8e
> --- /dev/null
> +++ b/Documentation/media/uapi/v4l/dev-decoder.rst

<cut>

> +Capture setup
> +=============
> +

<cut>

> +
> +2.  **Optional.** Acquire the visible resolution via
> +    :c:func:`VIDIOC_G_SELECTION`.
> +
> +    * **Required fields:**
> +
> +      ``type``
> +          a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``
> +
> +      ``target``
> +          set to ``V4L2_SEL_TGT_COMPOSE``
> +
> +    * **Return fields:**
> +
> +      ``r.left``, ``r.top``, ``r.width``, ``r.height``
> +          the visible rectangle; it must fit within the frame buffer resolution
> +          returned by :c:func:`VIDIOC_G_FMT` on ``CAPTURE``.
> +
> +    * The following selection targets are supported on ``CAPTURE``:
> +
> +      ``V4L2_SEL_TGT_CROP_BOUNDS``
> +          corresponds to the coded resolution of the stream
> +
> +      ``V4L2_SEL_TGT_CROP_DEFAULT``
> +          the rectangle covering the part of the ``CAPTURE`` buffer that
> +          contains meaningful picture data (visible area); width and height
> +          will be equal to the visible resolution of the stream
> +
> +      ``V4L2_SEL_TGT_CROP``
> +          the rectangle within the coded resolution to be output to
> +          ``CAPTURE``; defaults to ``V4L2_SEL_TGT_CROP_DEFAULT``; read-only on
> +          hardware without additional compose/scaling capabilities

Hans should correct me if I'm wrong but V4L2_SEL_TGT_CROP_xxx are
applicable over OUTPUT queue type?

> +
> +      ``V4L2_SEL_TGT_COMPOSE_BOUNDS``
> +          the maximum rectangle within a ``CAPTURE`` buffer, which the cropped
> +          frame can be output into; equal to ``V4L2_SEL_TGT_CROP`` if the
> +          hardware does not support compose/scaling
> +
> +      ``V4L2_SEL_TGT_COMPOSE_DEFAULT``
> +          equal to ``V4L2_SEL_TGT_CROP``
> +
> +      ``V4L2_SEL_TGT_COMPOSE``
> +          the rectangle inside a ``CAPTURE`` buffer into which the cropped
> +          frame is written; defaults to ``V4L2_SEL_TGT_COMPOSE_DEFAULT``;
> +          read-only on hardware without additional compose/scaling capabilities
> +
> +      ``V4L2_SEL_TGT_COMPOSE_PADDED``
> +          the rectangle inside a ``CAPTURE`` buffer which is overwritten by the
> +          hardware; equal to ``V4L2_SEL_TGT_COMPOSE`` if the hardware does not
> +          write padding pixels
> +
> +    .. warning::
> +
> +       The values are guaranteed to be meaningful only after the decoder
> +       successfully parses the stream metadata. The client must not rely on the
> +       query before that happens.
> +

-- 
regards,
Stan