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kox

Member

Registered: 2015-05-01

Posts: 146

[solved] Brightness control (xbacklight) randomly does not work

xbacklight -inc 5

Does nothing sometimes. Nothing relevant in the journals.

It works after a reboot for some time and that's the only thing that makes changing brightness possible.

Last edited by kox (2023-01-01 14:07:43)

Head_on_a_Stick

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From: London

Registered: 2014-02-20

Posts: 7,757

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Re: [solved] Brightness control (xbacklight) randomly does not work

Check the contents of /sys/class/backlight/ for both working and non-working instances. You've probably picked up a ACPI interface that's interfering with xbacklight.

If it exists try masking it:

# systemctl mask systemd-backlight@backlight:acpi_video0

^ That presumes the extra directory is called "acpi_video0", correct as needed.

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kox

Member

Registered: 2015-05-01

Posts: 146

Re: [solved] Brightness control (xbacklight) randomly does not work

It seems like it was affected by launching a gui as another user via xhost+ It does not occur anymore after updating packages.

kox

Member

Registered: 2015-05-01

Posts: 146

Re: [solved] Brightness control (xbacklight) randomly does not work

Unfortunately it's not solved. I still get this issue only now the trigger is different. I'm not 100% sure but now I think it breaks after screen sleep.

The contents of the directory is:

intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight

same in all instances.

So I did this:

[root@localhost]# systemctl mask systemd-backlight@backlight:intel_backlight
Created symlink /etc/systemd/system/systemd-backlight@backlight:intel_backlight.service → /dev/null.

but it does not fix it.

I think this could be a bug with  X.

Last edited by kox (2022-12-30 13:45:52)

V1del

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Registered: 2012-10-16

Posts: 21,811

Re: [solved] Brightness control (xbacklight) randomly does not work

Remove xf86-video-intel and stop using xbacklight but something remotely sane like acpilight (you can still use xbacklight in that case but it will actually manipulate the correct low level device instead of a weird xf86-video-intel specific trigger that breaks randomly)

Head_on_a_Stick

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From: London

Registered: 2014-02-20

Posts: 7,757

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Re: [solved] Brightness control (xbacklight) randomly does not work

So I did this:

[root@arch0 maciej]# systemctl mask systemd-backlight@backlight:intel_backlight
Created symlink /etc/systemd/system/systemd-backlight@backlight:intel_backlight.service → /dev/null.

My suggestion was to mask any *extra* backlight services. If you only have one directory in /sys/class/backlight/ then masking it will break the ability of systemd to restore the backlight level to whatever it was when the machine was last shutdown.

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kox

Member

Registered: 2015-05-01

Posts: 146

Re: [solved] Brightness control (xbacklight) randomly does not work

Thanks! Installing acpilight fixed the issue without even needing to restart.  (I removed the mask too). 

Why would I want to remove the video driver though? Is it not going to affect performance?

Head_on_a_Stick

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From: London

Registered: 2014-02-20

Posts: 7,757

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Re: [solved] Brightness control (xbacklight) randomly does not work

X's built-in modesetting driver will probably offer better performance and fewer bugs than xf86-video-intel.

https://dri.freedesktop.org/wiki/DDX/

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V1del

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Registered: 2012-10-16

Posts: 21,811

Re: [solved] Brightness control (xbacklight) randomly does not work

If your system is not over 10 years old modesetting will generally be the better option. Also on a sidenote, fix your hostname: https://wiki.archlinux.org/title/Networ … e_hostname -- localhost is a keyword and might run you into a variety of issues if retained as is.

kox

Member

Registered: 2015-05-01

Posts: 146

Re: [solved] Brightness control (xbacklight) randomly does not work

I see, thanks!