Can't change laptop screen backlight brightness after upgrading to 13.04

[Guest]

I have an Asus laptop that I installed 12.10 on some time ago. At first, I was unable to change the screen brightness via the keyboard or power management settings, but I was able to fix this by adding "acpi_backlight=vendor" to GRUB_CMDLINE_LINUX_DEFAULT in my GRUB settings. After upgrading to 13.04, this fix no longer works and I'm back to being unable to change the screen brightness. I've tried a fresh install of 13.04 as well, but that didn't solve the problem.

I suppose I should mention that with the "acpi_backlight=vendor" GRUB setting, I have two entries in /sys/class/backlight: "asus_laptop" and "intel_backlight".

When I press the brightness buttons on my keyboard, I see the value in /sys/class/backlight/asus_laptop/brightness changing (this is true for both 12.10 and 13.04). 12.10 would respond to changes in /sys/class/backlight/asus_laptop/brightness by changing my screen brightness. However, the trouble is that 13.04 doesn't respond to changes in that file. It responds to /sys/class/backlight/intel_backlight instead, but the brightness keys on my keyboard are still modifying the file in asus_laptop.

As a result, I can do

sudo echo 10 > /sys/class/backlight/intel_backlight/brightness

and my screen brightness changes accordingly. So I was trying to get the brightness controls to operate on intel_backlight instead of asus_laptop but I couldn't figure it out. It's a little bit frustrating that I am actually capable of changing the screen brightness but I can't configure the brightness controls to operate on the correct backlight :P

Any tips?

[Snowhog]

Try editing (as root) /etc/default/grub and add noapic to the GRUB_CMDLINE_LINUX= entry:

GRUB_CMDLINE_LINUX="noapic"

Save and close the file. Then in a console run:

sudo update-grub2

Log out and reboot. Try your brightness control keys when you are back in your Desktop.

[Guest]

Unfortunately that doesn't appear to change anything.

Edit: Ahah! I fixed it I found a kernel parameter to disable asus_backlight, which no longer doeess anything, forcing intel_backlight to be used instead. I can now adjust my screen brightness with the brightness control. I added this to GRUB_CMDLINE_LINUX_DEFAULT:

asus_laptop.backlight=0

[Snowhog]

Okay. Edit the file again. Make the following lines:

GRUB_CMDLINE_LINUX_DEFAULT=
GRUB_CMDLINE_LINUX=

Look like this:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux acpi_backlight=vendor" <<< add the bold text
GRUB_CMDLINE_LINUX=



Save and close and run again:

sudo update-grub2

[Teunis]

I once had such a problem with a Toshiba and noticed I could change the screen brightness during the boot phase, before X came up.
It's not a permanent solution but for me it worked until a proper solution came around.