[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 at oss.nxp.com wrote:
>>> From: Ming Qian <ming.qian at 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 at 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
> 

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@collabora.com/

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
>>>