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Subject: Re: [PATCH v9 2/9] media: v4l: Add definitions for MPEG-2 slice
 format and metadata
To:     Paul Kocialkowski <contact@paulk.fr>, linux-media@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, devel@driverdev.osuosl.org
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Chen-Yu Tsai <wens@csie.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        linux-sunxi@googlegroups.com, Randy Li <ayaka@soulik.info>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        Tomasz Figa <tfiga@chromium.org>,
        Alexandre Courbot <acourbot@chromium.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>
References: <20180906222442.14825-1-contact@paulk.fr>
 <20180906222442.14825-3-contact@paulk.fr>
From:   Hans Verkuil <hverkuil@xs4all.nl>
Message-ID: <3133cebf-2980-8f3d-4900-f410d4a704fc@xs4all.nl>
Date:   Mon, 10 Sep 2018 11:45:22 +0200
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On 09/07/2018 12:24 AM, Paul Kocialkowski wrote:
> From: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> 
> Stateless video decoding engines require both the MPEG-2 slices and
> associated metadata from the video stream in order to decode frames.
> 
> This introduces definitions for a new pixel format, describing buffers
> with MPEG-2 slice data, as well as control structure sfor passing the
> frame metadata to drivers.
> 
> This is based on work from both Florent Revest and Hugues Fruchet.
> 
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> ---
>  .../media/uapi/v4l/extended-controls.rst      | 176 ++++++++++++++++++
>  .../media/uapi/v4l/pixfmt-compressed.rst      |  16 ++
>  .../media/uapi/v4l/vidioc-queryctrl.rst       |  14 +-
>  .../media/videodev2.h.rst.exceptions          |   2 +
>  drivers/media/v4l2-core/v4l2-ctrls.c          |  63 +++++++
>  drivers/media/v4l2-core/v4l2-ioctl.c          |   1 +
>  include/media/v4l2-ctrls.h                    |  18 +-
>  include/uapi/linux/v4l2-controls.h            |  65 +++++++
>  include/uapi/linux/videodev2.h                |   5 +
>  9 files changed, 351 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/media/uapi/v4l/extended-controls.rst b/Documentation/media/uapi/v4l/extended-controls.rst
> index 9f7312bf3365..f1951236266a 100644
> --- a/Documentation/media/uapi/v4l/extended-controls.rst
> +++ b/Documentation/media/uapi/v4l/extended-controls.rst
> @@ -1497,6 +1497,182 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>  
>  
>  
> +.. _v4l2-mpeg-mpeg2:
> +
> +``V4L2_CID_MPEG_VIDEO_MPEG2_SLICE_PARAMS (struct)``
> +    Specifies the slice parameters (as extracted from the bitstream) for the
> +    associated MPEG-2 slice data. This includes the necessary parameters for
> +    configuring a stateless hardware decoding pipeline for MPEG-2.
> +    The bitstream parameters are defined according to :ref:`mpeg2part2`.
> +
> +.. c:type:: v4l2_ctrl_mpeg2_slice_params
> +
> +.. cssclass:: longtable
> +
> +.. flat-table:: struct v4l2_ctrl_mpeg2_slice_params
> +    :header-rows:  0
> +    :stub-columns: 0
> +    :widths:       1 1 2
> +
> +    * - __u32
> +      - ``bit_size``
> +      - Size (in bits) of the current slice data.
> +    * - __u32
> +      - ``data_bit_offset``
> +      - Offset (in bits) to the video data in the current slice data.
> +    * - struct :c:type:`v4l2_mpeg2_sequence`
> +      - ``sequence``
> +      - Structure with MPEG-2 sequence metadata, merging relevant fields from
> +	the sequence header and sequence extension parts of the bitstream.
> +    * - struct :c:type:`v4l2_mpeg2_picture`
> +      - ``picture``
> +      - Structure with MPEG-2 picture metadata, merging relevant fields from
> +	the picture header and picture coding extension parts of the bitstream.
> +    * - __u8
> +      - ``quantiser_scale_code``
> +      - Code used to determine the quantization scale to use for the IDCT.
> +    * - __u8
> +      - ``backward_ref_index``
> +      - Index for the V4L2 buffer to use as backward reference, used with
> +	B-coded and P-coded frames.
> +    * - __u8
> +      - ``forward_ref_index``
> +      - Index for the V4L2 buffer to use as forward reference, used with
> +	P-coded frames.

Do these indices refer to the output or capture buffers? I think these should
refer to the output buffers, since this control is used in a request for the
output side.

Regards,

	Hans