Bug 209055

Hello

The notebook is an Asus Zenbook 14' UM431D. I'm using KUbuntu 20.04.1, with Kernel 5.8.3 (Installed using Ubuntu Mainline Kernel Installer). The backlight keyboard have 4 levels (0 to 3, being 0 Off and 3 Max)

The only way to change the keyboard backlight brightness is the Fn+F7 key, it changes consecutively to the 4 levels of brightness: 0 (Off), 1, 2, 3 (Max).

The keyboard backlight status is currently and correctly detected for the KDE Plasma 5 enviroment battery and brightness status, but it can't change the status. Although, if you move the slider, to "2" when the backlight is off, the slider is misplaced by two if you change the backlight brightness via the Fn+F7 Key. The brightness or the volume is controlled perfectly via this control panel (although, the volume slider has other issue which seeems unrelated to this one https://bugzilla.kernel.org/show_bug.cgi?id=209053)

I tried "brightnessctl" command which also detects correctly the backlight info, but it can't change the brightness itself. If you set to 0, 1, 2 or 3, the backlight is off althought the Current brightness in the brightnessctl info is changed:

$ sudo brightnessctl --device 'asus::kbd_backlight' info
[sudo] contraseña para ******: 
Device 'asus::kbd_backlight' of class 'leds':
        Current brightness: 0 (0%)
        Max brightness: 3

brightnessctl current brightness also changes to the correct brightness level when using Fn+F7 key, but setting again via command line changes the info, but do nothing with the real brightness level.

The sys pseudo-file system which exposes the keyboard backlight interface is in /sys/class/leds/asus::kbd_backlight/.

$ ls -l /sys/class/leds/asus::kbd_backlight/
total 0
-rw-rw-r-- 1 root input 4096 ago 27 00:37 brightness
-r--r--r-- 1 root root  4096 ago 26 22:59 brightness_hw_changed
lrwxrwxrwx 1 root root     0 ago 27 00:26 device -> ../../../asus-nb-wmi
-r--r--r-- 1 root root  4096 ago 26 22:59 max_brightness
drwxr-xr-x 2 root root     0 ago 27 00:26 power
lrwxrwxrwx 1 root root     0 ago 26 22:59 subsystem -> ../../../../../class/leds
-rw-r--r-- 1 root root     0 ago 27 00:26 trigger
-rw-r--r-- 1 root root  4096 ago 26 22:59 uevent

The max_brightness file is always 3, and the brightness and the brightness_hw_changed files are updated with the correct level of brigthness selected with the Fn+F7 key (0 to 3). They  don't change with the KDE keyboard control slider, or the brightnessctl command, and the files can't be edited manually (including with root access).

What components are the affected to make the backlight keyboard controllable via software with my system? 

Thanks in advance.