[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 #5 from Rong Zhang (i@rong.moe) ---
Hi George,

Based on the debugfs dump and acpidump you provided, ideapad-laptop may not be
able to adjust keyboard backlight brightness as it does for other devices due
to the lack of relevant support in the ACPI table.

That being said, if you would like to debug more, enable dynamic debug for EC
with...

  echo file drivers/acpi/ec.c +p | sudo tee /proc/dynamic_debug/control

...and cycle through all keyboard backlight brightness levels. Then dump dmesg
to see if any EC queries were executed.

I also have a script (attached at the end) to dump the EC's MMIO region.
Dumping it with different keyboard brightness levels and comparing the dumps
may show some additional information:

  sudo bash /path/to/script.sh 0xFE00D400 0xFF 1

Note that dumping MMIO regions could be dangerous, so please save your open
files and sync them to the disk before running the script.

```bash
#!/bin/bash

err() {
        echo "$*" >&2
        exit 1
}

declare -i base=$1
declare -i len=$2
((base >= 0 && len > 0)) || err "Nothing to dump"

declare -l acc=$3
declare -A supp=(
        [1]=1 [2]=2 [4]=4 [8]=8
        [byte]=1 [word]=2 [dword]=4 [qword]=8
)
align=${supp[$acc]}
[[ -n "$align" ]] || err "Unsupported access type: $acc"
(( len < align )) && err "Length is too short: $len"
bits=$((align * 8))
mask=$((align - 1))
(( base & mask )) && err "Misaligned base: $base"

declare -A hex2bin=(
        [0]=0000 [1]=0001 [2]=0010 [3]=0011
        [4]=0100 [5]=0101 [6]=0110 [7]=0111
        [8]=1000 [9]=1001 [A]=1010 [B]=1011
        [C]=1100 [D]=1101 [E]=1110 [F]=1111
)
for ((off = base; off <= base + len - align; off += align)); do
        printf '0x%016X:' "$off"
        if ! out=$(busybox devmem "$off" "$bits" 2>&1); then
                echo " $out"
                continue
        fi
        printf -v hex "%0$((align * 2))X" "$((out))"
        for ((i = ${#hex} - 2; i >= 0; i -= 2)); do
                high=${hex:i:1}
                low=${hex:i+1:1}
                echo -n " ${hex2bin[$high]}${hex2bin[$low]}"
        done
        echo
done
```

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