[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

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            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

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

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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

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

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--- 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`.

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--- 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.

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--- 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.

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--- 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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--- 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!

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--- 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

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--- 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.

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

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--- 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.

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--- 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?

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--- 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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--- Comment #13 from George (george.stafilidis@proton.me) ---
I reinstalled Fedora on my laptop I somehow messed up what the power button
does.

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--- Comment #14 from Rong Zhang (i@rong.moe) ---
Hi George,

I am afraid you have somewhat overtrusted AI hallucinations...

(In reply to George from comment #12)
> 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.

Having all three states just means that the KBLC method correctly returns 0x5
when the first (and the only) argument is 0x1.

Except for that, everything goes wrong and has fundamental divergences from my
patch. The divergences make absolutely no sense to me. I don't believe your
device's keyboard backlight brightness has anything to do with KBLO and KLFS. I
will explain why later.

> 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.

What version? My patch or an AI-generated/modified one? Please attach it.

And please rollback to the version, it's probably a right step toward software
control. Then, set all three states via software, and dump 0xFE00D42A to see
what happens.

> Through EC memory dumping, I confirmed my laptop uses register 0x8A
> (not 0x2A as in the original patch), 

You confirmed, or AI confirmed?

Bit 0 of 0x8A is KBLO. AI must have seen the ASL code of other Lenovo laptops
during the pre-training stage, so it told you that "KBLO" is meant for keyboard
backlight brightness. Unfortunately, it makes no sense for your device. The
KBLO field and the SALS method exist on your device just because Lenovo
engineers produced a lot of dead code by copying and pasting ASL code across
different products and insanely "evolving" them. That's probably also the
reason why KLFS exists.

Meanwhile, these field names look like abbreviations and are very good at
causing AI hallucinations. AI will be easily stuck in its speculations for
absolutely no reason.

Your previous MMIO dumps have already proved that 0x2A is the offset we were
looking for. Your dumps are very similar to the ones on my device. Trust your
MMIO dumps, instead of AI.

> 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.

Completely AI hallucinations. In my patch, KLEN is located at bits 1-2 of 0x2A.
There is no chance that it overwrites UCHE at bit 1 of 0x8A. If something ever
inadvertently sets the UCHE bits, it must be an AI hallucination that puts KLEN
at bits 0-1 of 0x8A.

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

Your replies had too many divergences from my patch, which made me suspect
whether you've really tried my patch yourself instead of simply throwing it to
an AI. I'm not confident enough about the AI-generated answers or agentic
actions, either.

So, let's save each other's time. Ignore the instructions from AI, just answer
me:

What happened when you manually wrote the values you've found to 0xFE00D42A
through /dev/mem?

Have you ever tried my patch *without* any modifications? What was the exact
result when you applied it as is?

I've asked these questions before, and I am still waiting for your answers.

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--- Comment #15 from George (george.stafilidis@proton.me) ---
Sorry for my poor responses. English is not my first language, so there were
some things I didn't fully understand. I also used AI to help me with certain
parts because of the language barrier and because I haven't had much free time
due to exams.

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--- Comment #16 from George (george.stafilidis@proton.me) ---
Also, regarding your question: when I manually wrote values to /dev/mem, I
remember the software state cycling correctly through 0 (Off), 1 (Low), and 2
(High). However, the keyboard's physical backlight did not change.

I'm going to start over from scratch and repeat the process more carefully,
this time taking notes as I go instead of experimenting late at night and
relying on memory.

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--- Comment #17 from Rong Zhang (i@rong.moe) ---
(In reply to George from comment #13)
> I reinstalled Fedora on my laptop I somehow messed up what the power button
> does.

If acpi_listen can still see events from the power button, it's probably just a
configuration issue in GNOME.

(In reply to George from comment #15)
> Sorry for my poor responses. English is not my first language, so there were
> some things I didn't fully understand. I also used AI to help me with
> certain parts because of the language barrier

Well, you can ask me for more detailed explanations.

While AI is good at translating texts as is, things could go wrong when it
starts to explain them. Also, Qwen is not very good at these obscure issues, so
try not to push it too far.

> and because I haven't had much free time due to exams.

When I check Bugzilla, I usually take that as a casual pastime. In other words,
I'm not in a hurry to get your test results or feedback. You can take your
time. 

(In reply to George from comment #16)
> Also, regarding your question: when I manually wrote values to /dev/mem, I
> remember the software state cycling correctly through 0 (Off), 1 (Low), and
> 2 (High). However, the keyboard's physical backlight did not change.

Then the previous version of the DSDT code where "Off and Low worked physically
and the OSD appeared" (comment #12) is important. If possible, please attach it
in a reply.

> I'm going to start over from scratch and repeat the process more carefully,
> this time taking notes as I go instead of experimenting late at night and
> relying on memory.

Thanks.

Do experiments carefully, but keep a relaxed and casual attitude. You don't
need to do them overnight.

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--- Comment #18 from George (george.stafilidis@proton.me) ---
Created attachment 310272
  --> https://bugzilla.kernel.org/attachment.cgi?id=310272&action=edit
dump_off

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--- Comment #19 from George (george.stafilidis@proton.me) ---
Created attachment 310273
  --> https://bugzilla.kernel.org/attachment.cgi?id=310273&action=edit
dump_low

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--- Comment #20 from George (george.stafilidis@proton.me) ---
Created attachment 310274
  --> https://bugzilla.kernel.org/attachment.cgi?id=310274&action=edit
dump_high

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--- Comment #21 from George (george.stafilidis@proton.me) ---
Created attachment 310275
  --> https://bugzilla.kernel.org/attachment.cgi?id=310275&action=edit
dmesg_ec.txt

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--- Comment #22 from George (george.stafilidis@proton.me) ---
Thank you for the explanation and for your patience. I have attached
(dump_off.txt,dump_low.txt,dump_high.txt and dmesg_ec.txt) I hope i did it
correctly.


I did try the unmodified patch and from what i can see the GNOME Quick Settings
panel correctly displays all three states (Off, Low, High) but dotes not change
the brightness of they keyboard. Pressing Fn + Space correctly triggers the OSD
notification. i could upload a video if that's possible to show you what I can
see. (is it possible to upload mp4?)

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--- Comment #23 from Rong Zhang (i@rong.moe) ---
(In reply to George from comment #22)
> Thank you for the explanation and for your patience. I have attached
> (dump_off.txt,dump_low.txt,dump_high.txt and dmesg_ec.txt) I hope i did it
> correctly.

Thanks. It did seem that 0x2A controlled the keyboard backlight brightness.

> I did try the unmodified patch and from what i can see the GNOME Quick
> Settings panel correctly displays all three states (Off, Low, High) but
> dotes not change the brightness of they keyboard.

Given that neither my patch nor manually writing to 0x2A worked, I guess the EC
needs an additional synchronization mechanism to really trigger a brightness
change from register writing.

> Pressing Fn + Space
> correctly triggers the OSD notification. i could upload a video if that's
> possible to show you what I can see. (is it possible to upload mp4?)

You don't need to upload a video. For now, I need the previous version of the
DSDT code where "Off and Low worked physically and the OSD appeared" to figure
out what triggers the brightness change.

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--- Comment #24 from George (george.stafilidis@proton.me) ---
                            Method (KBLC, 1, Serialized)
                            {
                                Name (ICMD, Zero)
                                Name (IDTL, Zero)
                                Name (IDTH, Zero)
                                Name (RETD, Zero)
                                ICMD = (Arg0 & 0x0F)
                                IDTL = (Arg0 & 0xFFF0)
                                IDTL >>= 0x04
                                IDTH = (Arg0 & 0xFFFF0000)
                                IDTH >>= 0x10
                                RETD |= One
                                Switch (ToInteger (ICMD))
                                {
                                    Case (One)
                                    {
                                        Local0 = 0x02
                                        RETD |= Local0
                                    }
                                    Case (0x02)
                                    {
                                        Switch (ToInteger (IDTL))
                                        {
                                            Case (One)
                                            {
                                                Local0 = KLEN
                                                RETD |= Local0
                                            }
                                            Case (0x02)
                                            {
                                                Local0 = KLEN
                                                RETD |= Local0
                                            }
                                        }
                                    }
                                    Case (0x03)
                                    {
                                        Switch (ToInteger (IDTL))
                                        {
                                            Case (One)
                                            {
                                                Local0 = (IDTH & 0x03)
                                                KLEN = Local0
                                                RETD |= Local0
                                            }
                                            Case (0x02)
                                            {
                                                KLEN = IDTH
                                                RETD |= KLEN
                                            }
                                        }
                                    }
                                }
                                Return (ToInteger (RETD))
                            }

i think this is what you asking me to share with you. I think it is this
because I took a screenshot of what it did. The OSD notification when i applied
this version did not show up at all and only two options were showing in Quick
Settings: Off and High but both options were working when I clicked them (but
no osd). I think this is where Qwen got confused.

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--- 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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--- Comment #26 from George (george.stafilidis@proton.me) ---
Hi Rong,

I did the lid test exactly as you asked. I set the keyboard brightness to High
using Fn+Space. When I closed the lid, the keyboard light turned off after
about 5 seconds. When I opened the lid again, the light turned back on at High.
(Closing the lid when the keyboard light is off does not turn it open when i
open the lid)

I also ran the diff command on the MMIO dumps before closing and after opening
the lid. The output is:
2c2
< 0x00000000FE00D401: 00010000
---
> 0x00000000FE00D401: 00000001

7c7
< 0x00000000FE00D406: 00011100
---
> 0x00000000FE00D406: 00011010

177,178c177,178
< 0x00000000FE00D4B0: 00110010
< 0x00000000FE00D4B1: 00101100
---
> 0x00000000FE00D4B0: 00100110
> 0x00000000FE00D4B1: 00101010

184c184
< 0x00000000FE00D4B7: 00101000
---
> 0x00000000FE00D4B7: 00100111

199c199
< 0x00000000FE00D4C6: 00010010
---
> 0x00000000FE00D4C6: 00010011

I also did the manual test of register 0x8A as yoy asked

Step 3 (KBLO = 0, KLFS = 0): the light turned OFF
Step 4 (KBLO = 0, KLFS = 1): the light did not turn ON
Step 5 (KBLO = 1, KLFS = 0): the light turns ON at LOW brightness
Step 6 (KBLO = 1, KLFS = 1): the light stays at LOW brightness

Hopefully i got everything correct. I am also attaching the stock dsdt.

Oh  yeah also Bios info:
Version: GLCN68WW
Release Date: 03/19/2025

Have a wonderful night!

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--- Comment #27 from George (george.stafilidis@proton.me) ---
Created attachment 310277
  --> https://bugzilla.kernel.org/attachment.cgi?id=310277&action=edit
stock dsdt

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--- Comment #28 from Rong Zhang (i@rong.moe) ---
(In reply to George from comment #26)
> Hi Rong,
> 
> I did the lid test exactly as you asked. I set the keyboard brightness to
> High using Fn+Space.

What I said was "try writing to 0x2A, and ...". What value did you write?
Nothing? Or the High one? You would need to write a desired brightness value
other than the current physical one to 0x2A right before closing the lid.

> When I closed the lid, the keyboard light turned off
> after about 5 seconds. 

Hmm, after 5s? Most devices I met turn off the keyboard backlight immediately.

Please check if GNOME puts your laptop into suspend (sleep) after receiving a
lid event. If this is the case, please disable the feature in GNOME before
experimenting again.

> When I opened the lid again, the light turned back on
> at High. (Closing the lid when the keyboard light is off does not turn it
> open when i open the lid)
> 
> I also ran the diff command on the MMIO dumps before closing and after
> opening the lid.

Unfortunately, you dumped the MMIO region twice with the lid open: before
closing == lid is open; after opening == lid is open.

I need it once with the lid open and once with it closed (and *keep the lid
closed* while dumping). Basically, you would have to connect to an external
monitor to use the laptop with the lid closed, or use SSH.

> The output is:
> 2c2
> < 0x00000000FE00D401: 00010000
> ---
> > 0x00000000FE00D401: 00000001
> 
> 7c7
> < 0x00000000FE00D406: 00011100
> ---
> > 0x00000000FE00D406: 00011010
> 
> 177,178c177,178
> < 0x00000000FE00D4B0: 00110010
> < 0x00000000FE00D4B1: 00101100
> ---
> > 0x00000000FE00D4B0: 00100110
> > 0x00000000FE00D4B1: 00101010
> 
> 184c184
> < 0x00000000FE00D4B7: 00101000
> ---
> > 0x00000000FE00D4B7: 00100111
> 
> 199c199
> < 0x00000000FE00D4C6: 00010010
> ---
> > 0x00000000FE00D4C6: 00010011

Nothing looks special. They are just some volatile values related to thermal
states.

> 
> I also did the manual test of register 0x8A as yoy asked
> 
> Step 3 (KBLO = 0, KLFS = 0): the light turned OFF
> Step 4 (KBLO = 0, KLFS = 1): the light did not turn ON
> Step 5 (KBLO = 1, KLFS = 0): the light turns ON at LOW brightness
> Step 6 (KBLO = 1, KLFS = 1): the light stays at LOW brightness

During the test, what's the 0x2A value? In other words, where was the first
step?

Could you try the procedure below to see if it synchronizes the brightness:

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

And repeat the procedure with different brightness levels written to 0x2A.

> Hopefully i got everything correct.

You've done quite well, other than missing some pieces. Please address them in
your next reply.

> I am also attaching the stock dsdt.

It's not the one I asked. I asked for a full DSDT corresponding to the snippet
in comment 24, which returns 0x3 when the ICMD is 0x1. Your attachment returns
0x5.

Anyway, it's not important anymore, and you don't need to reupload it. Test
results for smashing KBLO are enough for me.

> 
> Oh  yeah also Bios info:
> Version: GLCN68WW
> Release Date: 03/19/2025

Fine, it's up to date. So an up-to-date BIOS can't fix this. Classic Lenovo
conduct, sigh.

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--- Comment #29 from Rong Zhang (i@rong.moe) ---
> 3. Same as 2, but KBLO=1

Sorry, I should be:

  4. Same as 3, but KBLO=1

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--- Comment #30 from George (george.stafilidis@proton.me) ---
> Hmm, after 5s? Most devices I met turn off the keyboard backlight
> immediately.

Sorry I meant to say that I opened the lid after 5 seconds the backlight did
turn off immediately. This is a translation error on my part.

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--- Comment #31 from George (george.stafilidis@proton.me) ---
Ok so I repeated the KBLO synchronization test.

First test:

Physical keyboard brightness was High.

sudo busybox devmem 0xFE00D42A 8
0x05

sudo busybox devmem 0xFE00D42A 8 0x03
sudo busybox devmem 0xFE00D48A 8 0x54
sudo busybox devmem 0xFE00D48A 8 0x55

Result:
The final command caused the keyboard backlight to turn on at Low brightness.

Second test:

sudo busybox devmem 0xFE00D42A 8 0x05
sudo busybox devmem 0xFE00D48A 8 0x54
sudo busybox devmem 0xFE00D48A 8 0x55

Result:
The final command again caused the keyboard backlight to turn on at Low
brightness.

So changing 0x2A before toggling 0x8A did not appear to affect the resulting
brightness. In both cases the keyboard came back at Low brightness. I am so
confused at this point I dont know if i am doing stuff the correct way.

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--- Comment #32 from Rong Zhang (i@rong.moe) ---
Then I doubt if clearing KBLO actually also clears 0x2A.

Try:

1. Set physical keyboard brightness to Low
2. sudo busybox devmem 0xFE00D42A 8 0x05
3. sudo busybox devmem 0xFE00D48A 8 0x54
4. sudo busybox devmem 0xFE00D42A 8
5. sudo busybox devmem 0xFE00D42A 8 0x05
6. sudo busybox devmem 0xFE00D48A 8 0x55

And also try:

1. Set physical keyboard brightness to Low
2. sudo busybox devmem 0xFE00D42A 8 0x05
3. Close the lid
4. Wait several seconds
5. Reopen the lid
6. sudo busybox devmem 0xFE00D42A 8

Please also try:

1. Set physical keyboard brightness to Low
2. sudo busybox devmem 0xFE00D42A 8 0x00
3. sudo busybox devmem 0xFE00D42A 8 0x05
4. sudo busybox devmem 0xFE00D42A 8 0x04
5. sudo busybox devmem 0xFE00D42A 8 0x05

I also have a slightly dangerous idea:

1. Set physical keyboard brightness to Low
2. sudo busybox devmem 0xFE00D42A 8 0x00
3. sudo busybox devmem 0xFE00D42A 8 0xFF
4. sudo busybox devmem 0xFE00D42A 8 0x05

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--- Comment #33 from George (george.stafilidis@proton.me) ---
ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0x05
[sudo] password for ultima: 
ultima@fedora:~$ sudo busybox devmem 0xFE00D48A 8 0x54
ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8
0x05
ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0x05
ultima@fedora:~$ sudo busybox devmem 0xFE00D48A 8 0x55
ultima@fedora:~$ 


last command did set it to low

ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0x05
ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8
0x05
ultima@fedora:~$ 


these did nothing


ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0x00
ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0x05
ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0x04
ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0x05
ultima@fedora:~$

these also did nothing 

ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0x00
ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0xFF
ultima@fedora:~$ sudo busybox devmem 0xFE00D42A 8 0x05
ultima@fedora:~$ 

also nothing here

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--- Comment #34 from Rong Zhang (i@rong.moe) ---
Hmm, let's try some radical approaches. There is still a chance that some
registers near 0x8A have something to do with the keyboard backlight
brightness.

1. Set physical keyboard brightness to Low
2. Backup 0x8A: sudo busybox devmem 0xFE00D48A 8
3. sudo busybox devmem 0xFE00D42A 8 0x05
4. sudo busybox devmem 0xFE00D48A 8 0x00
5. sudo busybox devmem 0xFE00D42A 8
6. sudo busybox devmem 0xFE00D42A 8 0x05
7. sudo busybox devmem 0xFE00D48A 8 0xFF
8. sudo busybox devmem 0xFE00D42A 8
9. Restore the backup of 0x8A: sudo busybox devmem 0xFE00D48A 8 <backup value>

REPEAT the same procedure, but replace 0x8A with 0x8B.
REPEAT with 0x8C.
REPEAT with 0x8D.

It could be dangerous as it massages a lot of bits. Be sure you have SSH access
before trying this, as it could turn off the backlight of the screen.

If massaging any of the four registers switches the brightness level to High,
stop experimenting and restore the backup of the register value.

If still no luck, you'd probably have to accept that it may not be possible to
set the brightness to High using software. I don't have any other idea, sigh.
Optimistically speaking, you can still switch between Off and Low using
software and get OSD work for all three states. If you can take that, I think I
can make a DSDT patch to achieve it.

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--- Comment #35 from George (george.stafilidis@proton.me) ---
Hi Rong,
I ran the radical approach test for 0x8A, 0x8B, 0x8C, and 0x8D. None of them
switched the brightness to High, and my screen backlight stayed on the whole
time. 
Since we couldn't find the High state, I would love to take your fallback
offer. Please let me know if you need anything else. Thank you so much for all
your help!

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Rong Zhang (i@rong.moe) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
 Attachment #310266|0                           |1
        is obsolete|                            |

--- Comment #36 from Rong Zhang (i@rong.moe) ---
Created attachment 310278
  --> https://bugzilla.kernel.org/attachment.cgi?id=310278&action=edit
DSDT patch (2nd attempt)

Hi George,

This DSDT patch should allow you to switch between Off and Low using software
and get OSD working for all three states.

Software will not prevent you from switching to High anyway, but the hardware
brightness will be Low.

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--- Comment #37 from George (george.stafilidis@proton.me) ---
Created attachment 310279
  --> https://bugzilla.kernel.org/attachment.cgi?id=310279&action=edit
Applied the patch

Hey Ron,

I’ve applied the patch and attached an MP4 so you can see what’s happening.
When I press Fn + Space, the OSD message appears correctly, and the quick
settings menu shows the keyboard button with Off / Low / High options. However,
the High setting doesn’t seem to have any effect.

Should this keyboard control button even be visible in this case, or did I mess
something up again?

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--- Comment #38 from George (george.stafilidis@proton.me) ---
Rong*

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--- Comment #39 from Rong Zhang (i@rong.moe) ---
Hi George,

That's expected. As I've said, "this DSDT patch should allow you to switch
between Off and Low using software", and "software *will not prevent* you from
switching to High anyway, but the hardware brightness will be Low."

The LED core of Linux does not allow different set and get capabilities. To
have a fully functional OSD, we must provide all three states with the side
effect of ineffective High when using software control. I believe it's the best
result we can achieve. Just ignore the High button :)

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--- Comment #40 from George (george.stafilidis@proton.me) ---
Thank you so much! How do I close this issue?

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--- Comment #41 from George (george.stafilidis@proton.me) ---
By the way, is there someone at Lenovo I could contact to ask what exactly
causes the keyboard to switch to the “high” state? I believe Lenovo has started
supporting LVFS, so maybe there’s a way to get more detailed information or
firmware insights through them?

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