Ubuntu – Cannot change backlight brightness Ubuntu 14.04

14.04backlightbrightnessintel graphics

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

Best Answer

I got a fix for my dell 5521 laptop, working for Ubuntu 14.04 but will work for kernels v3.13+.

  1. Open /etc/default/grub

    sudo nano /etc/default/grub

  2. to change the line 

    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

    to

    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=1"

  3. then save and exit and

  4. run

    sudo update-grub

  5. then reboot

The explanation is that ACPI adds its own back light control even if one is already present which is intel_backlight, adding this line forces CPI to use the Intel back light.

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