Bug#950609: systemd: backlight service messes with screen brightness

[Michael Biebl]

On Fri, 7 Feb 2020 20:29:25 +0100 Valerio Passini
<valerio.passini at unicam.it> wrote:
> Hi Michael,
> 
> Il Ven 7 Feb 2020, 19:05 Michael Biebl <biebl at debian.org> ha scritto:
> 
> > Control: tags -1 = moreinfo
> >
> > What exactly was not working? What did you do, what did you expect, what
> > did (not) happen.
> >
> 
> Screen brightness controls (the two keyboard buttons designed to tune
> brightness and the sliders in GNOME and KDE) are ineffective. If I press
> the buttons or I move the slider, the OSD shows that brightness is
changing
> while actually it's not. I expect that brightness is being regulated by my
> actions.
> 
> systemd-backlight at .service simply stores the current backlight value on
> > shutdown and restores it on boot.
> > It reads from /sys/class/backlight/*/brightness and writes accordingly.
> > If that somehow confuses the hardware, this smells like a driver/kernel
> > issue.
> >
> > Michael
> >
> 
> I know that it seems unrelated to systemd-backlight, that service should
> store and restore brightness through reboots, but here:
>
https://devtalk.nvidia.com/default/topic/1061387/linux/screen-brightness-resets-to-max-after-reboot-linux-/
> I have found that systemd-backlight is keeping brightness to maximum and
so
> I tried to disable it just to see if my problem would be fixed, and so it
> is.
> The real culprit might be something else as you said previously, but at
the
> moment it is a decent workaround for me and it might be worth
investigating
> it further.
> 
> Tell me if you need more info. Best regards

Is this problem still reproducible?
If so, is it specific to the proprietary NVIDIA driver or also reproducible
with the noveau driver?

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