linux-kernel - Re: [PATCH v2 1/3] media: v4l2-ctrls: Add average qp control

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Message-ID: <c9fdf07d-f434-430e-bb41-8bc8f6bf1bb8@collabora.com>
Date: Mon, 29 Apr 2024 19:38:32 +0200
From: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
To: Ming Qian <ming.qian@....com>, mchehab@...nel.org,
 hverkuil-cisco@...all.nl
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 v2 1/3] media: v4l2-ctrls: Add average qp control

Hi Ming Qian,

W dniu 25.04.2024 o 08:50, Ming Qian pisze:
> Add a control V4L2_CID_MPEG_VIDEO_AVERAGE_QP to report the average qp
> value of current encoded frame. the value applies to the last dequeued
> capture buffer.
> 
> Signed-off-by: Ming Qian <ming.qian@....com>
> ---
> v2
>   - improve document description according Hans's comments
>   - drop volatile flag
> 
>   Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 5 +++++
>   drivers/media/v4l2-core/v4l2-ctrls-defs.c                 | 5 +++++
>   include/uapi/linux/v4l2-controls.h                        | 2 ++
>   3 files changed, 12 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..7d82ab14b8ba 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -1653,6 +1653,11 @@ 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. The value applies to the last dequeued capture buffer
> +    (VIDIOC_DQBUF). Applicable to encoders.
> +

What is the intended range of the values? And why? Is your intention to make it
a hardware-agnostic control or a hardware-specific control?

Regrds,

Andrzej

>   .. 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..1ea52011247a 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> @@ -970,6 +970,7 @@ const char *v4l2_ctrl_get_name(u32 id)
>   	case V4L2_CID_MPEG_VIDEO_LTR_COUNT:			return "LTR Count";
>   	case V4L2_CID_MPEG_VIDEO_FRAME_LTR_INDEX:		return "Frame LTR Index";
>   	case V4L2_CID_MPEG_VIDEO_USE_LTR_FRAMES:		return "Use LTR Frames";
> +	case V4L2_CID_MPEG_VIDEO_AVERAGE_QP:			return "Average QP Value";
>   	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";
>   
> @@ -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_READ_ONLY;
> +		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)