Comment 95 for bug 1007765

May be the community is looking for the solution in the wrong direction.
Looking in /sys/class/backlight/ lists 3 folders on my Dell inspiron 7520.
One of the folders is intel_backlight .

Manually doing
root@Sirius:~# echo 2000 > /sys/class/backlight/intel_backlight/brightness
works.

This means that the problem is somewhere in the X configuration.

From a thread here https://bugs.freedesktop.org/show_bug.cgi?id=29273
I created an entry in xorg.conf

Section "Device"
        Option "Backlight" "intel_backlight"
        Identifier "Card0"
        Driver "intel"
        BusID "PCI:0:2:0"
EndSection

I created this by using X -c
and copying only relevant section to /etc/X11/xorg.conf

The controls are working fine now. I *do not* have acpi_backlight=vendor .
I just have acpi_osi=Linux , and I am not very sure if it is needed at all.