I am not able to change the brightness of the screen backlight with /sys/class/backlight/acpi_video0. actual_brightness and brightness both return 0 but the backlight is actually at full brightness.
I have tried passing acpi_osi=Linux acpi_backlight=vendor to linux but in that case /sys/class/backlight is empty.
After reading http://mjg59.livejournal.com/127103.html I am left with the impression that either I need a vendor module that does not exist or I should control the brightness via the GPU. The machine is a HP Pavilion DM1-4341 with a built in AMD Radeon HD 7340 Discrete-Class. I'm currently using the open source driver.
Does anyone have any suggestions?
I found that I first need to set the brightness of my graphics card interface to 0 before any changes to the acpi_video0 interface have any effect. In my case I alter the brightness file found in /sys/class/backlight/intel_backlight, which I assume corresponds to the Intel 3000 graphics card I have in my notebook.
Running following commands lets me change my screen brightness to a value x out of 15.:
# echo 0 > /sys/class/backlight/intel_backlight/brightness # echo x > /sys/class/backlight/acpi_video0/brightness
I would try setting the brightness of your specific GPU interface to 0 before modifying the acpi_video0 brightness, hopefully the solution can be applied in general.
Thank you for the response. I forgot to mention I only have acpi_video0 in my /sys/class/backlight/ directory. I will have to look into why the GPU brightness is not being registered.
Last edited by Fluxis (2013-01-15 19:49:04)