UPower only handles one kbd_backlight
Currently UPower only handles the first keyboard backlight it finds and ignores the rest: https://gitlab.freedesktop.org/upower/upower/-/blob/master/src/up-kbd-backlight.c#L264
However there are Laptops in the wild that have a multi zone (as in 3-zone or per-key) keyboard backlight with each it's own /sys/class/leds/kbd_backlight entry.
Also there can be the case that a laptop with backlight of the build in keyboard is used in conjunction with an external keyboard with built in backlight.
These keyboard backlights might not have the same max_brightness value
I see 2 ways UPower could handle this:
- Expose multiple KbdBacklights to the dbus
- Expose only one KbdBacklight that takes a percentage value that is applied to all keyboard backlights after being converted to the max_brightness range. This however would work kinda wirdly for backlights with only a few backlights steps (like when max_brightness is 2 for example -> off/half/full)
For reference, I'm coming from here: https://bugs.kde.org/show_bug.cgi?id=464751