Re: [PATCH v2 0/6] media: uvcvideo: Implement the Privacy GPIO as a subdevice

Hans Verkuil
2024-11-10T10:29:32Z

On 10/11/2024 11:02, Mauro Carvalho Chehab wrote:
> Em Sat, 9 Nov 2024 17:29:54 +0100
> Ricardo Ribalda <ribalda@chromium.org> escreveu:
>
>>>
>>> I think that should sort the issue, assuming that 1. above holds true.
>>>
>>> One downside is that this stops UVC button presses from working when
>>> not streaming. But userspace will typically only open the /dev/video#
>>> node if it plans to stream anyways so there should not be much of
>>> a difference wrt button press behavior.
>>
>> I do not personally use the button, but it is currently implemented as
>> a standard HID device.
>
> IMO, controlling the privacy via evdev is the best approach then. There's
> no need for a RW control neither at subdev or at device level. It could
> make sense a Read only to allow apps to read, but still it shall be up to
> the Kernel to protect the stream if the button is pressed.
>
>> Making it only work during streamon() might be
>> a bit weird.
>> I am afraid that if there is a button we should keep the current behaviour.
>
> Privacy matters only when streaming. IMO the Kernel check for it needs to
> be done at DQBUF time and at read() calls, as one can enable/disable the
> camera while doing videoconf calls. I do that a lot with app "soft" buttons,
> and on devices that physically support cutting the video.

We could add a vb2_s_privacy(bool privacy) function to vb2 to tell vb2 if the privacy
mode is on. And if so, take action. E.g. calling QBUF/DQBUF would return a -EACCES error.

That will ensure consistent behavior for all drivers that have a privacy function.

Note that there are two types of privacy GPIO: one that triggers when a physical
cover is moved, blocking the sensor, and one that is a button relying on software
to stop streaming video. In the first case it is informative, but you can keep
streaming.

Regards,

Hans

>
> I don't trust myself privacy soft buttons, specially when handled in userspace,
> so what I have are webcam covers (and a small stick glued at a laptop camera
> that has a too small sensor for a webcam cover). I only remove the cover/stick
> when I want to participate on videoconf with video enabled with the builtin
> camera.
>
> Regards
>
> Thanks,
> Mauro
>