[PATCH v2 3/5] media: v4l2-core: Add v4l2-stats interface
Detlev Casanova
detlev.casanova at collabora.com
Thu Jun 25 07:53:03 PDT 2026
Hi Hans,
On 6/19/26 09:05, Hans Verkuil wrote:
> 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 at 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 at 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 at 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?
I didn't want it either, but this will extend to other kind of drivers
and I couldn't find a type enum to rule them all.
Maybe just using Device Capabilities Flags ?
It still won't differentiate encoder from decoder.
I wouldn't super mad if we loose that information (userspace can simply
see it as a capture device) but it'd still be nice to have 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.
As mentioned in the other patch, "v4l2_metrics" is more accurate.
Detlev.
>
>> + 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
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