Re: [PATCH v3 0/5] media: Add fdinfo support for v4l2 drivers

[Detlev Casanova]

Hello !

Do you have any comment on this ?

Regards,
Detlev

On Monday, 6 July 2026 09:42:17 EDT Detlev Casanova wrote:
> fdinfo is useful to poll information from the driver.
> Unlike the ftrace interface, it lets userspace tools get a snapshot of
> the state of the driver at their own pace, instead of getting events for
> each driver status change.
> 
> This works better to get information like HW usage time or clock
> frequencies, as well as memory usage.
> This patch set focuses on mem2mem drivers that are per-frame based and
> an implementation is proposed for the Verisilicon Hantro and Rockchip
> rkvdec drivers, limited to main clock frequency and HW usage time, as
> well as HW cycles counting in Hantro.
> 
> Even though it is not used yet, per core fields are appended with
> `-<core_id>` to support multi-core drivers.
> 
> To ease support in drivers, a v4l2_metrics struct is added.
> It stores metrics information and provides helper functions to write
> the fdinfo file in a standard way.
> 
> An example of usage of this from userspace is implemented in v4l2top:
> 
> https://github.com/cazou/v4l2top (Check the upstream branch)
> 
> checkpatch.pl warning: The 2 arguments in the show_fdinfo callback
> definition are kept unnamed to match with the rest of the struct
> definition.
> 
> Signed-off-by: Detlev Casanova <detlev.casanova@xxxxxxxxxxxxx>
> ---
> Changes in v3:
> - Rename the fdinfo key prefix from "media-" to "v4l2-", and "stats" to
>   "metrics"
> - Restructure the documentation to have mandatory and optional keys
> - Add core ID to fields
> - Add HW cycles count support
> - Add ABI documentation
> - Link to v2:
> https://patch.msgid.link/20260617-v4l2-add-fdinfo-v2-0-d298e98ce06a@collabo
> ra.com
> 
> Changes in v2:
> - Simplify key/value pairs by removing repeated <eng> suffix
> - Add media type support
> - Add v4l2_stats helpers
> - Add support in rkvdec too
> - Link to v1:
> https://patch.msgid.link/20260612-v4l2-add-fdinfo-v1-0-723211abc861@collabo
> ra.com
> 
> To: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> To: Nicolas Dufresne <nicolas.dufresne@xxxxxxxxxxxxx>
> To: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
> To: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
> To: Detlev Casanova <detlev.casanova@xxxxxxxxxxxxx>
> To: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxxxxxxxxx>
> To: Heiko Stuebner <heiko@xxxxxxxxx>
> Cc: kernel@xxxxxxxxxxxxx
> Cc: linux-media@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-rockchip@xxxxxxxxxxxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> 
> ---
> Christopher Healy (2):
>       docs: media: add documentation for V4L2 driver usage metrics
>       media: hantro: Add per-context fdinfo usage metrics
> 
> Detlev Casanova (3):
>       media: v4l2: Add callback for show_fdinfo
>       media: v4l2-core: Add v4l2-metrics interface
>       media: rkvdec: Add per-context fdinfo usage metrics
> 
>  Documentation/ABI/testing/procfs-fdinfo-v4l2       | 129
> +++++++++++++++++++ .../userspace-api/media/drivers/index.rst          |  
> 1 +
>  .../media/drivers/v4l2-usage-metrics.rst           | 137
> +++++++++++++++++++++ drivers/media/platform/rockchip/rkvdec/rkvdec.c    | 
> 19 +++
>  drivers/media/platform/rockchip/rkvdec/rkvdec.h    |   1 +
>  drivers/media/platform/verisilicon/hantro.h        |   3 +
>  drivers/media/platform/verisilicon/hantro_drv.c    |  19 +++
>  drivers/media/platform/verisilicon/hantro_hw.h     |   1 +
>  .../platform/verisilicon/rockchip_vpu981_regs.h    |   1 +
>  .../media/platform/verisilicon/rockchip_vpu_hw.c   |   6 +
>  drivers/media/v4l2-core/Makefile                   |   2 +-
>  drivers/media/v4l2-core/v4l2-dev.c                 |  12 ++
>  drivers/media/v4l2-core/v4l2-fh.c                  |   3 +
>  drivers/media/v4l2-core/v4l2-metrics.c             |  78 ++++++++++++
>  include/media/v4l2-dev.h                           |   1 +
>  include/media/v4l2-fh.h                            |   2 +
>  include/media/v4l2-metrics.h                       |  47 +++++++
>  17 files changed, 461 insertions(+), 1 deletion(-)
> ---
> base-commit: 3c587e0b08bd3c4853a22792b9166b7457870165
> change-id: 20260610-v4l2-add-fdinfo-a790fceab329
> 
> Best regards,
> --
> Detlev Casanova <detlev.casanova@xxxxxxxxxxxxx>
> 
> 
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