Ubuntu – Brightness control on Samsung Ativ Book 6

I recently installed Ubuntu 14.04 on my Samsung Ativ Book 6 (NP680Z5E-X01US).

Since then I am completely unable to modify my brightness settings. The Fn buttons work fine, if I press Fn+F2/F3 I can see the brightness slider, but no change happens until I push it down to where it deactivates the screen. Also, there is no response from the keyboard backlight. Other work fine (audio, wifi, mousepad-lock)

I have tried several options and I am essentialy in the same spot of the user here:

Can't adjust brightness on my MSI VR420 laptop

What I tried:

• Edit /etc/default/grub ↦ GRUB_CMDLINE_LINUX_DEFAULT: acpi_osi=Linux,
  acpi_backlight=vendor (as well as several different combinations of
  these settings being on or off)

• Edit /etc/X11/xorg.conf (file doesn't exist on my system)

• sudo setpci -s 00:02.0 F4.B=XX (does nothing)

• xbacklight -set XX (does nothing)

• install indicator-brightness (changing its value does nothing)

Checking the folder

ls /sys/class/backlight/intel_backlight/

shows that

max_brightness = 4882

while

actual_brightness
brightness

change as I move the slider in step of 244, but no corresponding change in brightness happens.

My graphic card is

00:02.0 VGA compatible controller [0300]: Intel Corporation 3rd Gen Core processor Graphics Controller [8086:0166] (rev 09)       

I also have a Radeon

01:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Mars [Radeon HD 8670A/8670M/8750M] (rev ff)