Comment 35 for bug 954661

I have a brand new dell xps 13 (L321X). I downloaded the kernel from the Sputnik project but it didn't solved the problem of the backlight.
I tried also the method here:
http://askubuntu.com/questions/142017/brightness-keys-f4-and-f5-not-working-on-dell-xps-15-6-laptop
(change /etc/default/grub)
and here:
https://bugs.launchpad.net/ubuntu/+source/gnome-power-manager/+bug/762670
(add /etc/X11/xorg.conf)
but didn't help.

Any suggestions?