Ubuntu – GUI changes brightness in wrong /sys/class/backlight/*/brightness

12.04atibacklightgraphicstoshiba-satellite

When I use Fn+F6 / F7 (brighness down and up on Toshiba) the brightness notification opens up and responds, but the actual screen brightness remains unchanged. When I go to Settings > Brightness and adjust the slider, the same happens.

lspci reports my single graphics card: 01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Mobility Radeon HD 2400

I noticed both actions are taking effect on /sys/class/backlight/toshiba/brightness. When I manually change /sys/class/backlight/acpi_video0/brightness though, the screen finally lightens/darkens accordingly.

toshset reports "required kernel toshiba support not enabled." Installing toshiba-acpi-fix from ppa:keks9n/main doesn't work – install fails with:
"Reloading the module
ERROR: Module toshiba_acpi does not exist in /proc/modules
FATAL: Error inserting toshiba_acpi (/lib/modules/3.2.0-25-generic/kernel/drivers/platform/x86/toshiba_acpi.ko): No such device"

(By the way, I only tried toshset because I saw it suggest elsewhere it could help diagnose the problem. I have no intent or reason to install toshiba-acpi-fix unless it fixes the brightness issue.)

How do I make the system write to the right brightness control file? Is there any way to get rid of the invalid directory entry?

(By the way 2 folders in Sys/Class/Backlight? didn't help me.)

Best Answer

  • OK, between attempting suggested changes I left a acpi_backlight=vendor on the Grub command line. My command line Grub variables now read

    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
    GRUB_CMDLINE_LINUX="splash"
    

    My xorg.conf has the following on Device Section:

    Option "RegistryDwords" "EnableBrightnessControl=1"
    

    And everything is working as it should.