I lately had some problems changing my laptops (A Samsung Q45) brightness since the major distributions went on and started using KMS instead of the prior Xorg driver, even though most Samsung laptops aren’t properly supported. Searching around the net I found some hints about using setpci – Writing directly into the hardware.

dekar@vasectomy:~$ sudo dmidecode -s system-manufacturer
SAMSUNG ELECTRONICS CO., LTD.
dekar@vasectomy:~$ sudo dmidecode -s system-product-name
SQ45S70S
dekar@vasectomy:~$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller (rev 03)
dekar@vasectomy:~$ sudo setpci -s 00:02.0 F4.B=FF

Values between 0x00 and 0xFF should work, though my display turns off once I lower them too far and refuses to start working unless I reboot the whole thing. 0x40 to 0xFF should be safe.

Update:
The following samsung-backlight fork worked for me in fully integrating the backlight control again. Works fine now using the hotkeys 🙂
https://github.com/xonatius/samsung-backlight

You probably need to install the kernel sources, at least the headers. Besides this installing should be totally painless and after doing so you can load it using ‘modprobe samsung-backlight’.