Re: [RFC PATCH 1/7] media: v4l2-ctrls: Add V4L2_CID_MEMORY_USAGE control

[Nicolas Dufresne <nicolas@ndufresne.ca>]

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Le mardi 31 mars 2026 à 10:33 -0400, Frank Li a écrit :
> On Tue, Mar 31, 2026 at 03:23:11PM +0800, ming.qian@oss.nxp.com wrote:
> > From: Ming Qian <ming.qian@oss.nxp.com>
> > 
> > Add a new read-only control V4L2_CID_MEMORY_USAGE that allows
> > applications to query the total amount of memory currently used
> > by a device instance.
> > 
> > This control reports the memory consumption in bytes, including
> > internal buffers, intermediate processing data, and other
> > driver-managed allocations. Applications can use this information
> > for debugging, resource monitoring, or making informed decisions
> > about buffer allocation strategies.
> > 
> > Signed-off-by: Ming Qian <ming.qian@oss.nxp.com>
> > ---
> 
> Not sure why not export these information by debugfs, or any benefit vs
> debugfs?

There is also a on-going proposal that uses fdinfo.

Nicolas

> 
> Generanlly document should be first patch, then driver change.
> 
> Frank
> 
> >  drivers/media/v4l2-core/v4l2-ctrls-defs.c | 8 ++++++++
> >  include/uapi/linux/v4l2-controls.h        | 4 +++-
> >  2 files changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/v4l2-core/v4l2-ctrls-defs.c b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> > index 551426c4cd01..053db78ff661 100644
> > --- a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> > +++ b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> > @@ -831,6 +831,7 @@ const char *v4l2_ctrl_get_name(u32 id)
> >  	case V4L2_CID_ALPHA_COMPONENT:		return "Alpha Component";
> >  	case V4L2_CID_COLORFX_CBCR:		return "Color Effects, CbCr";
> >  	case V4L2_CID_COLORFX_RGB:              return "Color Effects, RGB";
> > +	case V4L2_CID_MEMORY_USAGE:		return "Memory Usage";
> > 
> >  	/*
> >  	 * Codec controls
> > @@ -1476,6 +1477,13 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
> >  		*min = 0;
> >  		*max = 0xffff;
> >  		break;
> > +	case V4L2_CID_MEMORY_USAGE:
> > +		*type = V4L2_CTRL_TYPE_INTEGER64;
> > +		*flags |= V4L2_CTRL_FLAG_READ_ONLY;
> > +		*min = 0;
> > +		*max = S64_MAX;
> > +		*step = 1;
> > +		break;
> >  	case V4L2_CID_FLASH_FAULT:
> >  	case V4L2_CID_JPEG_ACTIVE_MARKER:
> >  	case V4L2_CID_3A_LOCK:
> > diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> > index 68dd0c4e47b2..02c6f960d38e 100644
> > --- a/include/uapi/linux/v4l2-controls.h
> > +++ b/include/uapi/linux/v4l2-controls.h
> > @@ -110,8 +110,10 @@ enum v4l2_colorfx {
> >  #define V4L2_CID_COLORFX_CBCR			(V4L2_CID_BASE+42)
> >  #define V4L2_CID_COLORFX_RGB			(V4L2_CID_BASE+43)
> > 
> > +#define V4L2_CID_MEMORY_USAGE			(V4L2_CID_BASE+44)
> > +
> >  /* last CID + 1 */
> > -#define V4L2_CID_LASTP1                         (V4L2_CID_BASE+44)
> > +#define V4L2_CID_LASTP1                         (V4L2_CID_BASE+45)
> > 
> >  /* USER-class private control IDs */
> > 
> > --
> > 2.53.0
> > 

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