linux-kernel - Re: [PATCH RFC 0/3] meida: uvcvideo: reimplement privacy gpio as a separate subdevice

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Message-ID: <CANiDSCuq483Eha-KfUM_1y4zb0sC8rNgf-yki5SjiUo3czaKBw@mail.gmail.com>
Date:   Fri, 13 Jan 2023 09:25:52 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Yunke Cao <yunkec@...omium.org>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH RFC 0/3] meida: uvcvideo: reimplement privacy gpio as a
 separate subdevice

Hi Yunke

Thank you very much for the patchset :)

On Wed, 11 Jan 2023 at 09:52, Yunke Cao <yunkec@...omium.org> wrote:
>
> privacy_gpio in uvc were added as V4L2_CID_PRIVACY in uvc video node in
> https://lore.kernel.org/all/20201223133528.55014-1-ribalda@chromium.org/
>
> Userspace applications often require to constantly poll privacy control.
> Currently, polling privacy control requires keeping the video node open,
> which prevents the camera from autosuspending.
>
> This patchset adds a separate v4l2 subdevice. Userspace access the gpio
> via V4L2_CID_PRIVACY in the new subdevice. Applications can poll the
> privacy control status without opening the video node and activate the
> camera.
>
> The non-gpio V4L2_CID_PRIVACY in uvc is not affected.

Since this is a RFC, lets focus on the idea and not on the code itself.

- I am missing a reference to the subdevice from the media device. How
will a user figure out that /dev/v4l-subdev0 is the privacy gpio of
/dev/media0 and not /dev/media1?. Thake a look to the "ancillary
links"
- We have already exposed the control as part of the main video
device, that means that we need to keep that API. The control on
/dev/v4l-subdev0 should "mirror" the control on /dev/video0
- There is no need to v4l2_ctrl_fill_event(), if you modify the
control with a set controll function, the media controller should take
care of everything

@Sakari Ailus @Hans Verkuil : Assuming a correct implementation, how
would you feel about exposing a privacy gpio as a subdevice?


Thanks!!!


>
> Suggested-by: Ricardo Ribalda <ribalda@...omium.org>
> Signed-off-by: Yunke Cao <yunkec@...omium.org>
> ---
> Yunke Cao (3):
>       media: v4l2-ctrls: Expose v4l2_ctrl_fill_event()
>       media: uvcvideo: remove entity privacy control in the uvc video node
>       media: uvcvideo: reimplement privacy GPIO as a separate subdevice
>
>  drivers/media/usb/uvc/uvc_ctrl.c          | 17 -------
>  drivers/media/usb/uvc/uvc_driver.c        | 44 ++----------------
>  drivers/media/usb/uvc/uvc_entity.c        | 76 +++++++++++++++++++++++++++++++
>  drivers/media/usb/uvc/uvcvideo.h          | 19 +++++---
>  drivers/media/v4l2-core/v4l2-ctrls-core.c |  9 ++--
>  include/media/v4l2-ctrls.h                | 12 +++++
>  6 files changed, 111 insertions(+), 66 deletions(-)
> ---
> base-commit: 7dd4b804e08041ff56c88bdd8da742d14b17ed25
> change-id: 20230111-uvc_privacy_subdev-1e7a167e86eb
>
> Best regards,
> --
> Yunke Cao <yunkec@...omium.org>



-- 
Ricardo Ribalda