Fix backlight brightness

Backlight is not detected

So you've got a laptop and session level programs such as gnome-power-manager don't seem to detect a panel, or changes the brightness incorrectly. First we should check if the panel is detected by HAL. We can check laptop panel object using lshal:

[hughsie@work ~]$ lshal | grep laptop_panel
  info.capabilities = {'laptop_panel'} (string list)
  info.category = 'laptop_panel'  (string)
  laptop_panel.access_method = 'general'  (string)
  laptop_panel.brightness_in_hardware = true  (bool)
  laptop_panel.num_levels = 8  (0x8)  (int)

There's nothing detected!

Are you using a Lenovo 3k laptop? If so Lenovo have not exported standard controls using ACPI and do the action instead in hardware. Contact me if you want an experimental driver to allow reading the panel brightness, but not setting.

If you get no output on different hardware, then you probably need to do some research on the Internet. Interesting out of tree drivers to investigate are omnibook and sony.

I've got more than one laptop_panel device!

The video kernel acpi driver is buggy on quite a few IBM and Lenovo laptops. The quick fix is to rmmod video and then hopefully this only leaves one laptop panel.

You can stop the video module being loaded by doing:

[hughsie@work ~]$ su -l
Password: 
[root@work ~]# gedit /etc/modprobe.d/blacklist

Adding the following line to the end will prevent the module being loaded at boot.

blacklist video

My DELL hardware doesn't let me change the brightness after a suspend

Known problem, currently being debugged. For a quick fix solution just change to a text console using Ctrl-Alt-F1 and then back to the X console using Ctrl-Alt-F7. Brightness should then just work.

When I press brightness up the screen blanks

IBM/Lenovo laptop? See the fix above to remove the video module at boot.

When I press brightness up, the screen gets increased twice

Some laptops change the brightness in hardware and need to be added to a quirk database so session software such as gnome-power-manager is notified of the event, and then try to set a new brightness, when the hardware has already done so.

...add more content how to add a quirk...

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