Several days ago I tried to fix a quite popular problem. In my notebook the brightness control keys weren't working. I have added a file /usr/share/X11/xorg.conf.d/20-intel.conf
with following content:
Section "Device"
Identifier "card0"
Driver "intel"
Option "Backlight" "intel_backlight"
BusID "PCI:0:2:0"
EndSection

Now I can adjust the brightness, but every time when I reach the lowest brighness possible - it gets blocked and I cannot return to a higher level of brightness.
Have you encountered a similar problem? My computer is Samsung NP-R509.