[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 #25 from Rong Zhang (i@rong.moe) ---
So this version returns 0x3 when the ICMD is 0x1. However, ideapad-laptop only
accepts 0x5 and 0x7. With this version (it probably also has my modification to
HALS, i.e., `Local0 |= 0x10', right?), ideapad-laptop would use SALS to tune
the keyboard backlight instead.

Since I am not sure if Qwen made any other modifications to SALS or the address
of corresponding MMIO fields, please simply upload the full DSDT file of this
version.

If Qwen didn't modify SALS, it would tune the keyboard backlight by writing to
KBLO. Your previously attached DSDT
https://bugzilla.kernel.org/attachment.cgi?id=310268 also did this in KBLC, but
"clicking any of them has no effect on the physical backlight." Fine, we got
two inconsistent results on the same bit. The only difference in your attached
DSDT is that KLFS is also touched.

Could you try to massage 0x8A manually and check if the brightness changes?

1. Write a desired brightness level to 0x2A. It must be different from the
physical one
2. Read 0x8A
3. Manipulate the read value to make KBLO (bit 0) = 0 and KLFS (bit 4) = 0, and
write the modified value back to 0x8A
4. Same as 2, but KBLO=0, KLFS=1
5. Same as 2, but KBLO=1, KLFS=0
6. Same as 2, but KBLO=1, KLFS=1

You may repeat this procedure with different 0x2A values, i.e., brightness
levels.

Also, which BIOS version are you using (see dmidecode)? Sometimes, a BIOS
update might fix something, and you would probably want to try the latest one
(IIUC, it's GLCN68WW). I ask this because I found your device's ACPI tables
have no PNP0D80 for S0ix (which usually gives some clues on how to turn on/off
keyboard LEDs), but I did notice some S0ix-related mentions in the BIOS
changelog.

Another thought of mine is that you could try writing to 0x2A, and close and
reopen the lid to see if doing so updates the physical brightness. According to
my experience, closing the lid causes the EC to turn off the keyboard backlight
temporarily, and reopening it recovers the backlight. If doing so can
synchronize the brightness you've written to 0x2A, dump the EC's MMIO region,
once with the lid open and once with it closed.

Anyway, I am going to sleep now. I will reply to you when I wake up and decide
to have some casual pastimes.

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