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

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Date: Wed, 01 May 2024 15:55:46 -0400
From: Nicolas Dufresne <nicolas@...fresne.ca>
To: Hans Verkuil <hverkuil-cisco@...all.nl>, 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

Le mercredi 24 avril 2024 à 12:03 +0200, Hans Verkuil a écrit :
> 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.

Same question, though we should document the range, which will differ per-
codecs. We should also document to always use the specified range, rather then a
HW custom range. This way we don't endup with issues we have hit with other ill-
defined controls.

Nicolas

> 
> 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
>