Comment 2 for bug 1788021

Same problem on an Asus UX331U. In Ubuntu 18.04 setting kbd backlight worked, it's broken in Ubuntu 18.10.

Oct 1 17:43:19 avis gsd-power[2143]: gsd_power_backlight_abs_to_percentage: assertion 'max > min' failed

i am able to manually control the backlight on the shell using
sudo tee /sys/class/leds/asus\:\:kbd_backlight/brightness <<< 3

(replace 3 with [0..3] for brightness levels)

-----------------------------------

rephlex@avis:[/proc]: ls /sys/class/leds/
asus::kbd_backlight asus::lightbar asus-wireless::airplane input4::capslock input4::numlock input4::scrolllock phy0-led

-----------------------------------
root@avis:/sys/class/backlight# ls -la /sys/class/backlight/intel_backlight
lrwxrwxrwx 1 root root 0 Okt 1 17:44 /sys/class/backlight/intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight

root@avis:/sys/class/backlight# ls -la /sys/class/backlight/
insgesamt 0
drwxr-xr-x 2 root root 0 Okt 1 17:44 .
drwxr-xr-x 70 root root 0 Okt 1 17:40 ..
lrwxrwxrwx 1 root root 0 Okt 1 17:44 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight
------------------------------------