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

[Nicolas Dufresne]

Hi,

Le vendredi 29 mars 2024 à 18:23 +0900, Ming Qian a écrit :
> 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@xxxxxxx>
> ---
>  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.

That seems ambiguous at best. What does it mean the "currently encoded frame" ?
The OUTPUT and CAPTURE queue can be holding multiple frames. For "per frame"
accurate reporting, I feel like we'd need something like Hans' read-only
requests proposal [0]. Its basically a mechanism that let you attach request FD
to capture buffer, so that supported controls can be saved per v4l2-buffer and
read later on.

https://patches.linaro.org/project/linux-media/patch/20210610113615.785359-12-hverkuil-cisco@xxxxxxxxx/

If this isn't what you wanted, we'll need a better definition. It might be
helpful to explain what this is used for.

Nicolas

> +
>  .. 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";
>  
>  	/* 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;
> +		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)