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

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

[bugzilla-daemon]

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

            Bug ID: 221583
           Summary: Lenovo 82KU: keyboard backlight works via Fn+Space but
                    no kbd_backlight LED device exposed
           Product: Drivers
           Version: 2.5
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: Platform_x86
          Assignee: drivers_platform_x86@kernel-bugs.osdl.org
          Reporter: george.stafilidis@proton.me
        Regression: No

Laptop: Lenovo 82KU
Distribution: Fedora
Kernel: (paste output of uname -r)

Problem:
Keyboard backlight works correctly using Fn+Space
(Off -> Low -> High), but Linux exposes no keyboard
backlight LED interface.

No device appears under:
/sys/class/leds/

Expected behavior:
A standard LED interface such as:
platform::kbd_backlight
or
ideapad::kbd_backlight

Current result:
GNOME cannot expose keyboard backlight controls because
no LED device exists.

Tested:

* modprobe ideapad_laptop
* reboot
* latest Fedora updates

Outputs:

$ ls /sys/class/leds/
input18::capslock
input18::numlock
input18::scrolllock
input3::capslock
input3::numlock
input3::scrolllock
platform::fnlock

$ sudo dmidecode -s system-manufacturer
LENOVO

$ sudo dmidecode -s system-product-name
82KU

$ uname -r
7.0.10-200.fc44.x86_64

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

Rong Zhang (i@rong.moe) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |i@rong.moe

--- Comment #1 from Rong Zhang (i@rong.moe) ---
Hi George,

Could you please dump the files under /sys/kernel/debug/ideapad/ and attach
them when replying? Please also cycle the keyboard backlight brightness with
Fn+Space and see if it changes their content.

An acpidump will also be helpful.

Thanks,
Rong

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

--- Comment #2 from George (george.stafilidis@proton.me) ---
Created attachment 310234
  --> https://bugzilla.kernel.org/attachment.cgi?id=310234&action=edit
acpidump

Hi Rong,

I checked `/sys/kernel/debug/ideapad/`.

Directory contents:

```text
$ sudo ls -l /sys/kernel/debug/ideapad
total 0
-r--r--r--. 1 root root 0 Jun 1 17:23 cfg
-r--r--r--. 1 root root 0 Jun 1 17:23 status
```

These are the only files present:

```text
$ sudo find /sys/kernel/debug/ideapad -type f
/sys/kernel/debug/ideapad/status
/sys/kernel/debug/ideapad/cfg
```

Contents of `cfg`:

```text
_CFG: 0xfe0d0018

Capabilities: bluetooth wifi camera
OSD support: num-lock caps-lock mic-mute touchpad camera
Graphics:
```

Contents of `status`:

```text
Backlight max: 21
Backlight now: 17
BL power value: on (1)
=====================
Radio status: off (0)
Wifi status: off (0)
BT status: off (0)
3G status: off (0)
=====================
Touchpad status: on (1)
Camera status: on (1)
=====================
GBMD: 0x10060020
HALS: 0x0000ca40
```

I cycled the keyboard backlight through all states using Fn+Space (Off → Low →
High → Off), then compared the contents of both files before and after:

```text
$ diff -u ~/cfg-before.txt ~/cfg-after.txt
$ diff -u ~/status-before.txt ~/status-after.txt
```

Both commands produced no output.

I have attached `acpidump.txt.gz`.

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

--- Comment #3 from Rong Zhang (i@rong.moe) ---
(In reply to George from comment #2)
> HALS: 0x0000ca40

Your device reports itself as no keyboard backlight support.

> 
> I cycled the keyboard backlight through all states using Fn+Space (Off → Low
> → High → Off), then compared the contents of both files before and after:
> 
> ```text
> $ diff -u ~/cfg-before.txt ~/cfg-after.txt
> $ diff -u ~/status-before.txt ~/status-after.txt
> ```
> 
> Both commands produced no output.

Sorry, I meant you would need to check for content changes each time Fn+Space
is pressed, i.e., Off → Low, Low → High, High → Off.

> I have attached `acpidump.txt.gz`.

The HALS method seems to lack keyboard backlight stuff. But the SALS method can
be used to set a two-level backlight brightness (off, on), interesting. No
other ACPI method for keyboard backlight is found.

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

--- Comment #4 from George (george.stafilidis@proton.me) ---
Hi Rong,

I repeated the test while checking the debug files after each keyboard
backlight state transition:

* Off
* Low
* High

The contents of both `/sys/kernel/debug/ideapad/status` and
`/sys/kernel/debug/ideapad/cfg` remained identical in all three states.

Relevant values remained unchanged:

```text
HALS: 0x0000ca40
_CFG: 0xfe0d0018
```

No differences were observed when cycling the keyboard backlight with Fn+Space.

Please let me know if there are additional ACPI methods, traces, or debug
options that would be useful to collect.

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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
```

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

--- Comment #6 from George (george.stafilidis@proton.me) ---
Hi, following your advice, I dumped the EC MMIO region while cycling through
the keyboard backlight states. I found a consistent pattern at offset 0x2A
(Base address 0xFE00D400).
Here are the exact values read from 0xFE00D42A for each state:

    Backlight OFF: 0x00000000FE00D42A: 00000001 (Hex: 0x01)
    Backlight LOW: 0x00000000FE00D42A: 00000011 (Hex: 0x03)
    Backlight HIGH: 0x00000000FE00D42A: 00000101 (Hex: 0x05)

(Note: I identified the laptop in dmesg as ideapad_acpi VPC2004:00)
Could this offset be used to implement software control via the ideapad-laptop
driver or a custom ACPI method? Let me know if you need any further dumps or
testing!

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

--- Comment #7 from Rong Zhang (i@rong.moe) ---
Created attachment 310266
  --> https://bugzilla.kernel.org/attachment.cgi?id=310266&action=edit
DSDT patch

Hi George,

Thanks for debugging. Based on the information, software control should be
possible by overriding the device's DSDT with appropriate ACPI methods properly
implemented, which is (unfortunately) not upstreamable.

But as the first step, please try writing to the address via /dev/mem and see
if the keyboard backlight brightness changes (replace 0xXX with the values you
found):

  sudo busybox devmem 0xFE00D42A 8 0xXX

Writing to EC registers could be dangerous, so please be cautious.

I copied and pasted some code from my device's DSDT to create a DSDT patch for
your device. If writing to the address works, you may use it to provide the
required ACPI method to ideapad-laptop. I'm not an expert in writing ASL and
didn't test it at all, so there is a chance that things could go wrong. Be
cautious.

See
https://www.kernel.org/doc/html/latest/admin-guide/acpi/initrd_table_override.html
and https://wiki.archlinux.org/title/DSDT for detailed instructions on
overriding DSDT.

I'd recommend overriding it using GRUB2. See also
https://www.gnu.org/software/grub/manual/grub/html_node/acpi.html
If it ain't work, try GRUB_EARLY_INITRD_LINUX_CUSTOM. See
https://www.gnu.org/software/grub/manual/grub/html_node/Simple-configuration.html

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

--- Comment #8 from George (george.stafilidis@proton.me) ---
Created attachment 310267
  --> https://bugzilla.kernel.org/attachment.cgi?id=310267&action=edit
Keyboard showing up on quick settings

Hey, I'm not very good at writing ASL myself, so I asked Qwen to help. I
managed to get it to a point where the OSD popup was working and the keyboard
button showed up in Quick Settings, but it still wasn't changing the keyboard
backlight.

After some more tinkering, I got it so the Quick Settings button would switch
between Off and Low, but it still wouldn't go to High. At this point, I have no
idea what's going on.

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

--- Comment #9 from Rong Zhang (i@rong.moe) ---
I attached a DSDT patch in my previous reply. Did you try that?

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

--- Comment #10 from Rong Zhang (i@rong.moe) ---
IIUC, if you can only get Off and Low using my DSDT patch, you are probably
using an old kernel.

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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

--- Comment #11 from Rong Zhang (i@rong.moe) ---
Oh, you are using 7.0.x according to you first message. So that's not a
problem. Could you attach the final DSDT patch you applied?

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.

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

[bugzilla-daemon]

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.

-- 
You may reply to this email to add a comment.

You are receiving this mail because:
You are watching the assignee of the bug.