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SubjectRe: [PATCH v2 1/2] media: docs-rst: Document memory-to-memory video decoder interface
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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 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@chromium.org>
> ---
> 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

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