Arch Linux

dptkby

Member

Registered: 2009-07-02

Posts: 64

[MOSTLY SOLVED] Getting to the bottom of brightness problems

Hello!

While Linux generally works very nicely on my laptop (Acer 3820T) I, like many others, have problems with controlling brightness.

Out of the box, when trying to adjust brightness using keyboards, nothing happens. After appending acpi_osi=Linux to the kernel command line, things work perfectly all through the boot sequence... until Gnome starts. As what I assume is gnome-power-manager kicks in, adjustment becomes very choppy and unreliable... the indicator is often late, it can show the brightness changing even though it doesn't, and vice versa.

KDE seems to exhibit similar behaviour. The setpci method recommended on some sites does not do anything on my computer, neither does xbacklight or writing to /sys/class/backlight/acpi_video0/brightness (there is a file called "actual_brightness" which I can't write to).

Is it possible that the brightness change is entirely hardware-based and that Gnome only messes things up by trying to control it? I don't know anything about this subject and it seems to me there are a million places to start looking for the cause of the problems: gnome-power-manager, xrandr, graphics driver etc. Could anyone point me in the right direction?

Last edited by dptkby (2011-07-06 11:59:07)

StenM

Member

Registered: 2011-07-03

Posts: 33

Re: [MOSTLY SOLVED] Getting to the bottom of brightness problems

Try add to the kernel command line:
acpi_backlight=vendor
or
acpi_backlight=video

dptkby

Member

Registered: 2009-07-02

Posts: 64

Re: [MOSTLY SOLVED] Getting to the bottom of brightness problems

Try add to the kernel command line:
acpi_backlight=vendor
or
acpi_backlight=video

Thank you! acpi_backlight=vendor together with acpi_osi=Linux gives me the best results so far. However, the indicator still gets left behind if you change the brightness too quickly. It works well enough at the moment for me to be content, though, and I  really wasn't expecting a fix this easy, so thank you again!

litemotiv

Forum Fellow

Registered: 2008-08-01

Posts: 5,026

Re: [MOSTLY SOLVED] Getting to the bottom of brightness problems

Please mark your topic solved dptkby.

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