Arch Linux

sigru

Member

Registered: 2013-11-28

Posts: 2

Screen brightness keys (Fn+Home/End) not working on Thinkpad T25

Hi all,

I run Arch on a Thinkpad T25 ("Anniversary Edition"). The screen brightness keys (Fn+Home and Fn-End) used to work without problem, but that changed recently without any obvious reason. I use Gnome, but the problem seems to be independent of that. Here's what I can and cannot do:

- - -

Can do:

- change screen brightness by writing to /sys/class/backlight/intel_backlight/brightness
- change screen brightness using "xbacklight" and other tools
- change screen brightness using the "slider" in the Gnome settings menu

Cannot do:

- change screen brightness using Fn+Home/End

- - -

Based on various Wiki pages and forum posts, I tried the following things and observed the following changes:

1) check key codes with "xev" and "showkey"

Neither tool recognizes the Fn+Home/End combinations (i.e., no key codes shown). The Fn and Home/End buttons by themselved word fine. Other combinations of Fn+X show key codes and work as intended. I also tried "acpi_listen" with a ACPI daemon running in the background (which I normally don't use), but the result was the same.

There are also some keys which work despite not sending key codes (e.g., keyboard backlight). In addition, there are also some "unused" combinations such as Fn+Print and Fn+Pause that return key codes even thought they probably shouldn't.

2) set kernel parameter "acpi_backlight" and "acpi_osi" to different values

Setting "acpi_backlight=vendor" rendered the Fn+Home/End key functional (i.e., they returned key codes) but did not cause them to actually change the screen brightness. In addition, this broke screen brightness management in Gnome such that the brightness "slider" in the settings no longer worked. Pressing either button produced the expected screen overlay in Gnome that appears when screen brightness is adjusted, but the displayed values for minimim, maximum, and current brightness were incorrect.

I could use this and map the key codes directly to "xbacklight", but given the other problems this causes, I would consider this a very hacky solution. Setting "acpi_backlight" to other values caused no change ("native", "video", "none").

3) load "thinkpad-acpi" and "thinkpad_acpi" kernel modules

No change.

4) set option "Backlight" to "intel_backlight" in xorg.conf

No change

- - -

In summary, the issues with screen brightness seem to be superficial, and the real problem seems to be with the keys not being recognized correctly. Does anybody have experience with similar issues or ideas on how I can get the Fn+Home/End keys to work and control screen brightness as intended?

Thanks in advance!
Simon