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

[Frank Li]

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?

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
>