linux-kernel - Re: [PATCH 1/2] media: v4l2-ctrls: Add average qp control

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Message-ID: <25a33db9-3bc1-4d90-83d4-0bdbea9bc5d8@xs4all.nl>
Date: Wed, 24 Apr 2024 12:03:44 +0200
From: Hans Verkuil <hverkuil-cisco@...all.nl>
To: Ming Qian <ming.qian@....com>, mchehab@...nel.org
Cc: shawnguo@...nel.org, robh+dt@...nel.org, s.hauer@...gutronix.de,
 kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
 xiahong.bao@....com, eagle.zhou@....com, tao.jiang_2@....com,
 ming.qian@....nxp.com, imx@...ts.linux.dev, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] media: v4l2-ctrls: Add average qp control

On 29/03/2024 10:23, Ming Qian wrote:
> Add a control V4L2_CID_MPEG_VIDEO_AVERAGE_QP to report the average qp
> value of current encoded frame.
> 
> Signed-off-by: Ming Qian <ming.qian@....com>
> ---
>  Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 4 ++++
>  drivers/media/v4l2-core/v4l2-ctrls-defs.c                 | 5 +++++
>  include/uapi/linux/v4l2-controls.h                        | 2 ++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index 2a165ae063fb..cef20b3f54ca 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -1653,6 +1653,10 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>      Quantization parameter for a P frame for FWHT. Valid range: from 1
>      to 31.
>  
> +``V4L2_CID_MPEG_VIDEO_AVERAGE_QP (integer)``
> +    This read-only control returns the average qp value of the currently
> +    encoded frame. Applicable to the H264 and HEVC encoders.

qp -> QP

Why is this applicable to H264/HEVC only? I think it is fine for any codec.

This needs to document that the value applies to the last dequeued buffer
(VIDIOC_DQBUF).

> +
>  .. raw:: latex
>  
>      \normalsize
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-defs.c b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> index 8696eb1cdd61..88e86e4e539d 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> @@ -972,6 +972,7 @@ const char *v4l2_ctrl_get_name(u32 id)
>  	case V4L2_CID_MPEG_VIDEO_USE_LTR_FRAMES:		return "Use LTR Frames";
>  	case V4L2_CID_FWHT_I_FRAME_QP:				return "FWHT I-Frame QP Value";
>  	case V4L2_CID_FWHT_P_FRAME_QP:				return "FWHT P-Frame QP Value";
> +	case V4L2_CID_MPEG_VIDEO_AVERAGE_QP:			return "Average QP value";

value -> Value

Also move it up two lines so that it follows V4L2_CID_MPEG_VIDEO_USE_LTR_FRAMES
rather than FWHT controls.

>  
>  	/* VPX controls */
>  	case V4L2_CID_MPEG_VIDEO_VPX_NUM_PARTITIONS:		return "VPX Number of Partitions";
> @@ -1507,6 +1508,10 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>  		*max = 0xffffffffffffLL;
>  		*step = 1;
>  		break;
> +	case V4L2_CID_MPEG_VIDEO_AVERAGE_QP:
> +		*type = V4L2_CTRL_TYPE_INTEGER;
> +		*flags |= V4L2_CTRL_FLAG_VOLATILE | V4L2_CTRL_FLAG_READ_ONLY;

Drop the volatile flag, this isn't a volatile value.

> +		break;
>  	case V4L2_CID_PIXEL_RATE:
>  		*type = V4L2_CTRL_TYPE_INTEGER64;
>  		*flags |= V4L2_CTRL_FLAG_READ_ONLY;
> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> index 99c3f5e99da7..974fd254e573 100644
> --- a/include/uapi/linux/v4l2-controls.h
> +++ b/include/uapi/linux/v4l2-controls.h
> @@ -898,6 +898,8 @@ enum v4l2_mpeg_video_av1_level {
>  	V4L2_MPEG_VIDEO_AV1_LEVEL_7_3 = 23
>  };
>  
> +#define V4L2_CID_MPEG_VIDEO_AVERAGE_QP  (V4L2_CID_CODEC_BASE + 657)
> +
>  /*  MPEG-class control IDs specific to the CX2341x driver as defined by V4L2 */
>  #define V4L2_CID_CODEC_CX2341X_BASE				(V4L2_CTRL_CLASS_CODEC | 0x1000)
>  #define V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE		(V4L2_CID_CODEC_CX2341X_BASE+0)

Regards,

	Hans