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Subject: Re: [RFC 07/12] media: uapi: h264: Add DPB entry field reference
 flags
From:   Ezequiel Garcia <ezequiel@collabora.com>
To:     Jonas Karlman <jonas@kwiboo.se>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Boris Brezillon <boris.brezillon@collabora.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
        "linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
        "linux-rockchip@lists.infradead.org" 
        <linux-rockchip@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Date:   Fri, 10 Jul 2020 01:21:07 -0300
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Hello Jonas,

In the context of the uAPI cleanup,
I'm revisiting this patch.

On Sun, 2019-09-01 at 12:45 +0000, Jonas Karlman wrote:
> Add DPB entry flags to help indicate when a reference frame is a field picture
> and how the DPB entry is referenced, top or bottom field or full frame.
> 
> Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
> ---
>  Documentation/media/uapi/v4l/ext-ctrls-codec.rst | 12 ++++++++++++
>  include/media/h264-ctrls.h                       |  4 ++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> index bc5dd8e76567..eb6c32668ad7 100644
> --- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> @@ -2022,6 +2022,18 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>      * - ``V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM``
>        - 0x00000004
>        - The DPB entry is a long term reference frame
> +    * - ``V4L2_H264_DPB_ENTRY_FLAG_FIELD_PICTURE``
> +      - 0x00000008
> +      - The DPB entry is a field picture
> +    * - ``V4L2_H264_DPB_ENTRY_FLAG_REF_TOP``
> +      - 0x00000010
> +      - The DPB entry is a top field reference
> +    * - ``V4L2_H264_DPB_ENTRY_FLAG_REF_BOTTOM``
> +      - 0x00000020
> +      - The DPB entry is a bottom field reference
> +    * - ``V4L2_H264_DPB_ENTRY_FLAG_REF_FRAME``
> +      - 0x00000030
> +      - The DPB entry is a reference frame
>  
>  ``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE (enum)``
>      Specifies the decoding mode to use. Currently exposes slice-based and
> diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> index e877bf1d537c..76020ebd1e6c 100644
> --- a/include/media/h264-ctrls.h
> +++ b/include/media/h264-ctrls.h
> @@ -185,6 +185,10 @@ struct v4l2_ctrl_h264_slice_params {
>  #define V4L2_H264_DPB_ENTRY_FLAG_VALID		0x01
>  #define V4L2_H264_DPB_ENTRY_FLAG_ACTIVE		0x02
>  #define V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM	0x04
> +#define V4L2_H264_DPB_ENTRY_FLAG_FIELD_PICTURE	0x08
> +#define V4L2_H264_DPB_ENTRY_FLAG_REF_TOP	0x10
> +#define V4L2_H264_DPB_ENTRY_FLAG_REF_BOTTOM	0x20
> +#define V4L2_H264_DPB_ENTRY_FLAG_REF_FRAME	0x30
>  

I've been going thru the H264 spec and I'm unsure,
are all these flags semantically needed?

For instance, if one of REF_BOTTOM or REF_TOP (or both)
are set, doesn't that indicate it's a field picture?

Or conversely, if neither REF_BOTTOM or REF_TOP are set,
then it's a frame picture?

Thanks,
Ezequiel