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

[Ming Qian(OSS)]

Hi Nicolas,

On 3/31/2026 10:54 PM, Nicolas Dufresne wrote:
> 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@xxxxxxxxxxx wrote:
> > > From: Ming Qian <ming.qian@xxxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxxx>
> > > ---
> >
> > 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

Thanks for the reminder about the ongoing fdinfo proposal.

Just to confirm, you are referring to Detlev’s ongoing fdinfo proposal,
specifically this series:
https://lore.kernel.org/lkml/20260212162328.192217-1-detlev.casanova@xxxxxxxxxxxxx/

I will align my work with it and switch to using fdinfo.
Once the show_fdinfo support from that series is merged, I will prepare
the next revision of my patch accordingly.

Regards,
Ming

> > 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