I happened to do some extra testing. Searching the web, found the way to manually change screen brightness.
I have investigated and there the interface is up, and reports as following:
OpenELEC-T440p:~ # ls /sys/class/backlight/intel_backlight/
actual_brightness device subsystem
bl_power max_brightness type
brightness power uevent
I can then issue a command to change backlight to an arbitrary value:
echo XXX > /sys/class/backlight/intel_backlight/brightness
Where XXX is a value between 0 (backlight off) and max_brightness (4794 for this particular model).
So apparently the issue is related to the keys themselves not responding or setting the change.
I am not very acknowledgeable in any way with scripting, but I guess that it should be fairly simple to create a script that could increment or decrement by 10% (1/10th of the max-min brightness) and assign it to a Kodi key.
Can anyone help me to achieve this?
Thanks!