This morning I found that I cannot change the brightness of my Dell XPs 13 laptop's display anymore. I tried the following to change the brightness
- Use keyboard brightness keys
- Run the commands shown below
- Boot with kernel option acpi_backlight=vendor. This resulted in a dell_something folder being present in the /sys/class/backlight folder. Changing the brightness file in that folder does not help.
- Add 'intel_backlight' to xorg.conf
- Set "load legacy option ROM" BIOS option to enabled and "secure boot" to disabled
- Boot with kernel option i915.disable-pch_pwm=0
- Boot from a fresh Ubuntu 12.04 USB stick installation. I can still not control the brightness. This is strange as the laptop came preinstalled with 12.04. Maybe this a hardware problem?
- Install latest intel video driver
Any ideas why this broke suddendly? I've upgraded from 12.04 to 14.04 in April and till yesterday the brightness keys were working fine.
Thanks!
echo 100 > /sys/class/backlight/intel_backlight/brightness
echo 100 > /sys/class/backlight/acpi_video0/brightness