[Bug 221583] Lenovo 82KU: keyboard backlight works via Fn+Space but no kbd_backlight LED device exposed

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=221583

--- Comment #12 from George (george.stafilidis@proton.me) ---
Created attachment 310268
  --> https://bugzilla.kernel.org/attachment.cgi?id=310268&action=edit
current dsdt.dsl

Hi Rong,
I’ve attached my current dsdt.dsl. With this version, the GNOME Quick Settings
panel correctly displays all three states (Off, Low, High), but clicking any of
them has no effect on the physical backlight. Additionally, pressing Fn+Space
no longer triggers the OSD popup at all.

For context, I previously had a version where Off and Low worked physically and
the OSD appeared, but selecting High would instantly reset the state to Off.
Through EC memory dumping, I confirmed my laptop uses register 0x8A (not 0x2A
as in the original patch), and that writing 0x02 to the 2-bit KLEN field
inadvertently sets the UCHE (USB Charging) bit, which cuts power to the
backlight or whatever qwant thinks I have no idea.

I’m not confident enough in ASL to resolve this safely.

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