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

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Date:   Tue, 14 Feb 2023 14:45:57 +0900
From:   Yunke Cao <yunkec@...omium.org>
To:     Ricardo Ribalda <ribalda@...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!

On Fri, Jan 13, 2023 at 5:26 PM Ricardo Ribalda <ribalda@...omium.org> wrote:
>
> 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

Thanks! I will fix these in the next version if we decide to proceed.

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

Sakari, Hans, do you think this idea makes sense?

Best,
Yunke

>
> 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