Put in
/usr/share/X11/xorg.conf.d/20-intel.conf
20-intel.conf
Section "Device"
Identifier "card0"
Driver "intel"
Option "Backlight" "intel_backlight"
BusID "PCI:0:2:0"
EndSection
root@uranix:/usr/share/X11/xorg.conf.d# ls -ltr
total 36
-rw-r--r-- 1 root root 842 fév 5 2014 50-wacom.conf
-rw-r--r-- 1 root root 364 fév 5 2014 11-evdev-trackpoint.conf
-rw-r--r-- 1 root root 590 fév 5 2014 11-evdev-quirks.conf
-rw-r--r-- 1 root root 115 fév 5 2014 50-vmmouse.conf
-rw-r--r-- 1 root root 590 avr 10 2014 51-synaptics-quirks.conf
-rw-r--r-- 1 root root 1757 avr 10 2014 50-synaptics.conf
-rw-r--r-- 1 root root 1867 fév 12 15:51 10-quirks.conf
-rw-r--r-- 1 root root 1099 fév 12 15:51 10-evdev.conf
-rw-r--r-- 1 root root 167 mar 26 09:57 20-intel.conf
Now brightness control work fine.
