Re: [PATCH v2 3/5] media: v4l2-core: Add v4l2-stats interface

[Hans Verkuil <hverkuil+cisco@kernel.org>]

On 17/06/2026 20:10, Detlev Casanova wrote:
> Provide helpers for media drivers to set fdinfo data and print the
> key:value pairs in a standard way.
> 
> User drivers can set stats values with helpers like:
>  - v4l2_stats_update_hw_usage
>  - v4l2_stats_set_media_dev_type
> 
> And also call the show helpers from their show_fdinfo callback with:
>  - v4l2_stats_show -- Shows the values set previously
>  - v4l2_stats_show_clock -- Shows the main clock state.
> 
> The show_clock helper is used instead of updating a clock value in
> v4l2_stats for the following reasons:
>  - Clocks are at the device level, this is not a per-fd information
>  - This avoids having clock references in v4l2-core
>  - Drivers can use different approaches to manage clocks
>    (e.g.: bulk_data or not: A set helper wouldn't please all drivers)
>  - Arguably, clocks could be exposed elsewhere (like a debugfs), but we
>    want something close to what DRM does and centralizing information has
>    its advantages for userspace tooling.
> 
> In DRM the key:value pair format for clocks is documented and each driver
> can write them directly based on that.
> In this case, provide a helper and document the format.
> 
> Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>
> ---
>  drivers/media/v4l2-core/Makefile     |  2 +-
>  drivers/media/v4l2-core/v4l2-dev.c   |  2 ++
>  drivers/media/v4l2-core/v4l2-fh.c    |  3 ++
>  drivers/media/v4l2-core/v4l2-stats.c | 65 ++++++++++++++++++++++++++++++++++++
>  include/media/v4l2-fh.h              |  2 ++
>  include/media/v4l2-stats.h           | 44 ++++++++++++++++++++++++
>  6 files changed, 117 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/v4l2-core/Makefile b/drivers/media/v4l2-core/Makefile
> index 329f0eadce99..20e1ab74ac09 100644
> --- a/drivers/media/v4l2-core/Makefile
> +++ b/drivers/media/v4l2-core/Makefile
> @@ -9,7 +9,7 @@ ccflags-y += -I$(srctree)/drivers/media/tuners
>  tuner-objs	:=	tuner-core.o
>  
>  videodev-objs	:=	v4l2-dev.o v4l2-ioctl.o v4l2-device.o v4l2-fh.o \
> -			v4l2-event.o v4l2-subdev.o v4l2-common.o \
> +			v4l2-event.o v4l2-subdev.o v4l2-common.o v4l2-stats.o \
>  			v4l2-ctrls-core.o v4l2-ctrls-api.o \
>  			v4l2-ctrls-request.o v4l2-ctrls-defs.o
>  
> diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> index 3878fa2ff73e..3e7a6876dffd 100644
> --- a/drivers/media/v4l2-core/v4l2-dev.c
> +++ b/drivers/media/v4l2-core/v4l2-dev.c
> @@ -486,6 +486,8 @@ static void v4l2_show_fdinfo(struct seq_file *m, struct file *filp)
>  {
>  	struct video_device *vdev = video_devdata(filp);
>  
> +	seq_printf(m, "media-driver:\t%s\n", vdev->v4l2_dev->name);
> +
>  	if (vdev->fops->show_fdinfo)
>  		vdev->fops->show_fdinfo(m, filp);
>  }
> diff --git a/drivers/media/v4l2-core/v4l2-fh.c b/drivers/media/v4l2-core/v4l2-fh.c
> index b184bed8aca9..1b655672c718 100644
> --- a/drivers/media/v4l2-core/v4l2-fh.c
> +++ b/drivers/media/v4l2-core/v4l2-fh.c
> @@ -17,6 +17,7 @@
>  #include <media/v4l2-event.h>
>  #include <media/v4l2-ioctl.h>
>  #include <media/v4l2-mc.h>
> +#include <media/v4l2-stats.h>
>  
>  void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev)
>  {
> @@ -38,6 +39,7 @@ void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev)
>  	INIT_LIST_HEAD(&fh->subscribed);
>  	fh->sequence = -1;
>  	mutex_init(&fh->subscribe_lock);
> +	v4l2_stats_init(&fh->stats);
>  }
>  EXPORT_SYMBOL_GPL(v4l2_fh_init);
>  
> @@ -88,6 +90,7 @@ void v4l2_fh_exit(struct v4l2_fh *fh)
>  	v4l2_event_unsubscribe_all(fh);
>  	mutex_destroy(&fh->subscribe_lock);
>  	fh->vdev = NULL;
> +	v4l2_stats_exit(&fh->stats);
>  }
>  EXPORT_SYMBOL_GPL(v4l2_fh_exit);
>  
> diff --git a/drivers/media/v4l2-core/v4l2-stats.c b/drivers/media/v4l2-core/v4l2-stats.c
> new file mode 100644
> index 000000000000..93e64ef2e7bb
> --- /dev/null
> +++ b/drivers/media/v4l2-core/v4l2-stats.c
> @@ -0,0 +1,65 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * v4l2-stats.c
> + *
> + * V4L2 statistics management.
> + *
> + * Maintain a per-file handle list of statistics about the hardware and handle
> + * exposing it in the fdinfo.
> + *
> + * Copyright (C) 2026 Collabora.
> + *
> + * Contact: Detlev Casanova <detlev.casanova@collabora.com>
> + */
> +
> +#include <linux/types.h>
> +#include <linux/seq_file.h>
> +#include <linux/clk.h>
> +#include <media/v4l2-stats.h>
> +
> +static const char * const dev_type_name[] = {
> +	[MEDIA_DEV_TYPE_V4L2] = "media",
> +	[MEDIA_DEV_TYPE_V4L2_STATELESS_ENCODER] = "encoder",
> +	[MEDIA_DEV_TYPE_V4L2_STATELESS_DECODER] = "decoder",
> +};
> +
> +void v4l2_stats_init(struct v4l2_stats *stats)
> +{
> +	stats->hw_usage_time = 0;
> +	stats->media_dev_type = MEDIA_DEV_TYPE_V4L2;
> +}
> +
> +void v4l2_stats_exit(struct v4l2_stats *stats)
> +{
> +}
> +
> +void v4l2_stats_update_hw_usage(struct v4l2_stats *stats, u64 usage_time)
> +{
> +	stats->hw_usage_time += usage_time;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_stats_update_hw_usage);
> +
> +void v4l2_stats_set_media_dev_type(struct v4l2_stats *stats, enum v4l2_media_dev_type type)
> +{
> +	if (type >= MEDIA_DEV_TYPE_COUNT)
> +		return;
> +
> +	stats->media_dev_type = type;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_stats_set_media_dev_type);
> +
> +void v4l2_stats_show(struct v4l2_stats *stats, struct seq_file *m)
> +{
> +	seq_printf(m, "media-type:\t%s\n", dev_type_name[stats->media_dev_type]);
> +	seq_printf(m, "media-engine-usage:\t%llu ns\n", stats->hw_usage_time);
> +}
> +EXPORT_SYMBOL_GPL(v4l2_stats_show);
> +
> +void v4l2_stats_show_clock(struct seq_file *m, struct clk *clk)
> +{
> +	seq_printf(m, "media-maxfreq:\t%lu Hz\n",
> +		   clk_get_rate(clk));
> +	seq_printf(m, "media-curfreq:\t%lu Hz\n",
> +		   clk_get_rate(clk));
> +}
> +EXPORT_SYMBOL_GPL(v4l2_stats_show_clock);
> diff --git a/include/media/v4l2-fh.h b/include/media/v4l2-fh.h
> index aad4b3689d7e..ae6688722bee 100644
> --- a/include/media/v4l2-fh.h
> +++ b/include/media/v4l2-fh.h
> @@ -17,6 +17,7 @@
>  #include <linux/kconfig.h>
>  #include <linux/list.h>
>  #include <linux/videodev2.h>
> +#include <media/v4l2-stats.h>
>  
>  struct video_device;
>  struct v4l2_ctrl_handler;
> @@ -43,6 +44,7 @@ struct v4l2_fh {
>  	struct list_head	list;
>  	struct video_device	*vdev;
>  	struct v4l2_ctrl_handler *ctrl_handler;
> +	struct v4l2_stats	stats;
>  	enum v4l2_priority	prio;
>  
>  	/* Events */
> diff --git a/include/media/v4l2-stats.h b/include/media/v4l2-stats.h
> new file mode 100644
> index 000000000000..d580933c4181
> --- /dev/null
> +++ b/include/media/v4l2-stats.h
> @@ -0,0 +1,44 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * v4l2-stats.h
> + *
> + * V4L2 statistics management.
> + *
> + * Maintain a per-file handle list of statistics about the hardware and handle
> + * exposing it in the fdinfo.
> + *
> + * Copyright (C) 2026 Collabora.
> + *
> + * Contact: Detlev Casanova <detlev.casanova@collabora.com>
> + */
> +#ifndef V4L2_STATS_H
> +#define V4L2_STATS_H
> +
> +#include <linux/types.h>
> +
> +struct clk;
> +struct seq_file;
> +
> +enum v4l2_media_dev_type {
> +	MEDIA_DEV_TYPE_V4L2 = 0,
> +	MEDIA_DEV_TYPE_V4L2_STATELESS_ENCODER,
> +	MEDIA_DEV_TYPE_V4L2_STATELESS_DECODER,
> +
> +	MEDIA_DEV_TYPE_COUNT,

I'm a bit unhappy about introducing yet another type. Do we need it?

> +};
> +
> +struct v4l2_stats {

Poor name, and it conflicts with ISP statistics.

How about v4l2_pdinfo? And v4l2-fdinfo.h etc. That avoids any confusion and
also clearly says what this is about.

> +	u64 hw_usage_time;
> +	enum v4l2_media_dev_type media_dev_type;

This should be the first field.

> +};
> +
> +void v4l2_stats_init(struct v4l2_stats *stats);
> +void v4l2_stats_exit(struct v4l2_stats *stats);
> +
> +void v4l2_stats_update_hw_usage(struct v4l2_stats *stats, u64 usage_time);
> +void v4l2_stats_set_media_dev_type(struct v4l2_stats *stats, enum v4l2_media_dev_type type);
> +
> +void v4l2_stats_show(struct v4l2_stats *stats, struct seq_file *m);
> +void v4l2_stats_show_clock(struct seq_file *m, struct clk *clk);
> +
> +#endif /* V4L2_STATS_H */
> 

Regards,

	Hans