HP ELITEBOOK 8470p FIX Brightness control UBUNTU 14.04

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.