Controlling Backlight on Dell XPS-13 in Fedora 18
I just bought a Dell XPS-13 which comes installed with Ubuntu. I didn't want that, so I installed Fedora 18 from a USB stick. I did test a bit with the shipped OS and all the power management stuff Just Works(tm).
The first thing I noticed after installing Fedora was that the display backlight controls were inoperative. The OSD pops up displaying the brightness level when you press one of the keys to control brightness or when, due to idle, the power management function adjusts the brightness. Doing some searches on Google turned up the suggestion to do this to enable the backlight control:
echo 0 >/sys/class/backlight/intel_backlight/brightness
Well, that immediately enables the backlight controls and all appears to work fine. For a while. Eventually the system reverts to the disabled state on backlight control.
I don't know what all this means. I read that a bug on the kernel should be opened in this case and someone has done that, BZ 928688.
But in the mean time, I figured out how to work around this problem more effectively. Here's a small daemon that starts up at boot-time and watches for changes to the backlight level and continuously re-enables the function when it "sees" a change.
Just unpack it and do the following:
make PREFIX=/usr/local sudo -E make install sudo systemctl start backlight.service
That's it. The service will start up at boot-time and continuously re-enable the backlight control whenever it is changed by keys or power management.