linux-kernel - Re: [PATCH 4/4] media: uvcvideo: Introduce allow_privacy

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Message-ID: <374afd7b45297979278d02f6b06abaed35c12eae.camel@irl.hu>
Date: Tue, 18 Nov 2025 16:36:55 +0100
From: Gergo Koteles <soyer@....hu>
To: Hans de Goede <hansg@...nel.org>,
  Ricardo Ribalda <ribalda@...omium.org>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
  Mauro Carvalho Chehab <mchehab@...nel.org>,
  Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
  linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
  linux-usb@...r.kernel.org
Subject: Re: [PATCH 4/4] media: uvcvideo: Introduce allow_privacy_override

Hi Hans,

On Tue, 2025-11-18 at 15:26 +0100, Hans de Goede wrote:

> 
> > > Do you have a compelling use-case for turning off the privacy LED?
> > > 
> > 
> > As a pet camera, it is useful to be able to turn off the LED.
> > In some cases, it can also eliminate unwanted reflections.
> > Some cameras may have blue LED, and if someone hates blue LEDs..
> 
> And almost all cameras already do not allow manually overriding the LED
> turning on while streaming. There is a very low-tech solution for this,
> put some black isolation tape over the LED :)
> 

Yes, this is also a good and stable solution. :)

> > > My core goal is simple: if the camera is in use, the privacy LED must
> > > be ON. If the LED is ON unexpectedly, it serves as a clear indication
> > > that something unusual is happening.
> 
> ...
> 
> > > No freedom is lost. This change simply increases the
> > > trustworthiness/reliability of your device.
> > 
> > It will decrease to the extent that fewer people will know that such an
> > option exists because they will not read the description of the
> > module's parameters.
> 
> People currently already will not know that the option exists.
> 
> Seeing the current LED controls on Logitech cams requires 2 manual steps:
> 
> 1. Install uvcdynctrl which maps the custom GUIDs to the LED controls
>    Note distros do not install this be default
> 2. Use either a GUI v4l2-control app like qv4l2ucp or gtk-v4l, or
>    v4l-ctrl -l to list controls and then change the setting.
> 
> So there already is close to 0 discoverability for this Logitech
> only feature.

This is not completely true.
The cameractrls uses these extensions and controls with
uvc_xu_control_query() and has over 140k downloads on Flathub alone.

> 
> For the new MIPI cameras on laptops we have deliberately made it
> impossible to disable the privacy LED while streaming even though
> it is often controlled by a separate GPIO because of privacy reasons.
> 
> For the same privacy reasons I fully agree with Ricardo that this should
> be behind a module option. Which replaces step 1. with creating
> a /etc/modprobe.d/uvc.conf file, so just about as much work.
> 

I agree that this will be useful. The module parameter is also simpler
than per-V4L2 control permission management. And the latter is not
needed in other cases, I think.

However, if allow_privacy_override is enabled, would it be worth
mapping these controls by the kernel?
So uvcdynctrl or cameractrls would not be needed for this control.
> 

Regards,
Gergo