Comment # 36 on bug 1180591 from Takashi Iwai

(In reply to Marcel Kuehlhorn from comment #35)
> (In reply to Miroslav Bene������ from comment #34)
> > It has been a while. There is a much newer kernel version in TW now. Does
> > the issue still persist with that? It could be the case, since it looks like
> > a problem with BIOS or ACPI.
> 
> In fact I have just recently also started seeing this issue on Tumbleweed
> 
> It was still working about a week ago for me and now neither the
> xfce4-power-manager nor xbacklight are able to change screen brightness

That's weird.  xfce4-power-manager should access directly /sys/class/backlight
stuff (via xfpm-power-backlight-helper), at least.  If changing the sysfs entry
directly works, it should work, too.

There seems to have had some breakage and got fixed in TW about
xfce4-power-manager (bsc#1202125).  Could you recheck?

> > # xbacklight -set 100
> > RANDR Query Version returned error -1

If any, this must be an issue in user-space, not kernel.

> Using the method of writing to /sys with echo does work for me:
> > echo 378 > /sys/devices/pci0000\:00/0000\:00\:02.0/drm/card1/card1-eDP-1/intel_backlight/brightness