Controlling screen brightness on HP ProBook 4540s in Fedora 20

Controlling screen brightness on HP ProBook 4540s in Fedora 20

Everything on my HP ProBook 4540s works out of the box in Fedora 20 except the screen brightness control. The brightness is always 100% which just burns my eyes badly. When I press the shortcuts on the keyboard to adjust the brightness, I can see a KDE bar pops up in the center of the screen and the percentage changes, but no actual brightness is changed. If I leave the laptop for long enough, Fedora is able to turn the screen off. But once I start using the laptop, the brightness is back to 100% again. So there is no gray area between the black and the white.

I first found out that I was able to control through manipulating /sys/class/backlight/intel_backlight:

  1. [she@localhost ~]$ su
  2. Password:
  3. [root@localhost she]# cat /sys/class/backlight/intel_backlight/max_brightness
  4. 3484
  5. [root@localhost she]# echo 2000 > /sys/class/backlight/intel_backlight/brightness
  6. [root@localhost she]# cat /sys/class/backlight/intel_backlight/actual_brightness
  7. 2000
  8. [root@localhost she]#

The echo command is able to change the screen brightness. Note that the max_brightness has a value of 3484 in my case, so it is not a percentage. Any non-negative value smaller than 3484 works for me.

Then I added acpi_backlight=vendor to kernel boot parameters as in the following:

[root@localhost class]# vim /etc/default/grub

append acpi_backlight=vendor to GRUB_CMDLINE_LINUX, so it looks like

GRUB_CMDLINE_LINUX=" vconsole.font=latarcyrheb-sun16 $([ -x /usr/sbin/rhcrashkernel-param ] &&
/usr/sbin/rhcrashkernel-param || :) rhgb quiet acpi_backlight=vendor"

finally, run the command below and restart after that.

[root@localhost class]# grub2-mkconfig -o /boot/grub2/grub.cfg

Before this, there was acpi_video0 together with intel_backlight under /sys/class/backlight, but now there is only intel_backlight.

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