linux-kernel - Re: [RFC v2 09/10] media: uapi: h264: Add DPB entry field reference flags

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Message-ID: <20191031112056.3442d6ac@collabora.com>
Date:   Thu, 31 Oct 2019 11:20:56 +0100
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Jonas Karlman <jonas@...boo.se>
Cc:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Tomasz Figa <tfiga@...omium.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v2 09/10] media: uapi: h264: Add DPB entry field reference
 flags

On Tue, 29 Oct 2019 01:26:01 +0000
Jonas Karlman <jonas@...boo.se> 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@...boo.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 28313c0f4e7c..d472a54d1c4d 100644
> --- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> @@ -2028,6 +2028,18 @@ 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 don't remember all the details, but do we really need 3 flags?
Maybe I'm wrong, but it looks like the following combination doesn't
make sense:

- FIELD_PICTURE + REF_FRAME: if it's a full frame ref it should
  contain both top and bottom fields right, so it's no longer a
  FIELD_PICTURE, is it?

Can't we just have 2 flags?

FIELD_PICTURE		0x08
FIELD_REF_TOP		0x10 (meaning that FIELD_REF_BOTTOM is
			      0x00)

and then have the following combinations:

top field ref => FIELD_PICTURE | FIELD_REF_TOP
bottom field ref => FIELD_PICTURE
full frame ref => 0x0

>  
>  struct v4l2_h264_dpb_entry {
>  	__u64 reference_ts;