[SOLVED] laptop brightness keys no longer work

[o5gmmob8]

My function keys to control the laptop screen brightness no longer work. It seemed to happen all of a sudden, I don't believe I performed any system updates or anything.

I am still able to control the brightness via xbacklight -set 100, but I have to do that as root.

dmesg ACPI errors:

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[Tue Jan 27 18:20:04 2026] acpi-tad ACPI000E:00: Missing _PRW
[Tue Jan 27 18:20:05 2026] ACPI Error: Needed [Buffer/String/Package], found [Integer] 000000007ebda429 (20240827/exresop-557)
[Tue Jan 27 18:20:05 2026] ACPI Error: AE_AML_OPERAND_TYPE, While resolving operands for [OpcodeName unavailable] (20240827/dswexec-433)
[Tue Jan 27 18:20:05 2026] ACPI Error: Aborting method \_SB.WMID.WHCM due to previous error (AE_AML_OPERAND_TYPE) (20240827/psparse-529)
[Tue Jan 27 18:20:05 2026] ACPI Error: Aborting method \_SB.WMID.WMAA due to previous error (AE_AML_OPERAND_TYPE) (20240827/psparse-529)
[Tue Jan 27 18:20:05 2026] ACPI Error: Needed [Buffer/String/Package], found [Integer] 00000000b087e2af (20240827/exresop-557)
[Tue Jan 27 18:20:05 2026] ACPI Error: AE_AML_OPERAND_TYPE, While resolving operands for [OpcodeName unavailable] (20240827/dswexec-433)
[Tue Jan 27 18:20:05 2026] ACPI Error: Aborting method \_SB.WMID.WHCM due to previous error (AE_AML_OPERAND_TYPE) (20240827/psparse-529)
[Tue Jan 27 18:20:05 2026] ACPI Error: Aborting method \_SB.WMID.WMAA due to previous error (AE_AML_OPERAND_TYPE) (20240827/psparse-529)
[Tue Jan 27 20:15:22 2026] ACPI: EC: interrupt blocked
[Tue Jan 27 20:36:02 2026] ACPI BIOS Error (bug): Could not resolve symbol [^^^^NPCF.DTGP], AE_NOT_FOUND (20240827/psargs-332)
[Tue Jan 27 20:36:02 2026] ACPI Error: Aborting method \_SB.PCI0.LPC0.EC0._Q37 due to previous error (AE_NOT_FOUND) (20240827/psparse-529)
[Tue Jan 27 21:33:30 2026] ACPI BIOS Error (bug): Could not resolve symbol [\_SB.PCI0.LPCB.BAT1], AE_NOT_FOUND (20240827/psargs-332)
[Tue Jan 27 21:33:30 2026] ACPI Error: Aborting method \_SB.PEP._DSM due to previous error (AE_NOT_FOUND) (20240827/psparse-529)
[Tue Jan 27 21:33:30 2026] ACPI: EC: interrupt unblocked

Dmesg output when pressing brightness function keys

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[Wed Jan 28 12:05:06 2026] atkbd serio0: Unknown key released (translated set 2, code 0xab on isa0060/serio0).
[Wed Jan 28 12:05:06 2026] atkbd serio0: Use 'setkeycodes e02b <keycode>' to make it known.

I rebooted to see if that might help, but it did not. I'm thinking that somehow, perhaps the firmware got corrupted. I am running an update now to see if that *MAY* help.

I don't know if it is worth mentioning here, but my dmesg output has the wrong time, whereas date has the correct time. It is off by ~ 1h 15m which does not correspond to my timezone offset. I tried to sync my RTC, but had no such luck.

Any ideas would be greatly appreciated.

[turtles]

EC typically means Embedded Controller,

Could not resolve symbol [\_SB.PCI0.LPCB.BAT1], AE_NOT_FOUND in \_SB.PEP._DSM

Firmware is likely referencing a battery object BAT1 that is not present.
Are you running openrc or systemd?
Wayland or xorg?

On a xorg system you run

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xev -event keyboard

it opens up a window and you can debug the brightness keys.

you might also check out app-misc/evtest



I'd investigate if you changed users groups / permissions recently.
check for changed udev rules or conflicting ones:

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grep -RIns --color=auto 'backlight\|brightness\|acpilight' /etc/udev/rules.d /lib/udev/rules.d 2>/dev/null

I think wayland and x can both provide a command called xbacklight I dont know if they both behave exactly the same but check which one you have:

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which xbacklight
xbacklight -h 2>&1 | head
equery b "$(which xbacklight)"    # or: qfile "$(which xbacklight)"

[turtles]

On laptops I have used this to debug if you run this as root it will report if the kernel is getting the keypresses from the embedded controller;

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dev=$(ls -1 /sys/class/backlight 2>/dev/null | head -n1) || exit 1
b="/sys/class/backlight/$dev/brightness"
ab="/sys/class/backlight/$dev/actual_brightness"

echo "device=$dev"
old="$(cat "$ab" 2>/dev/null || cat "$b")"
echo "start=$old"

while :; do
  new="$(cat "$ab" 2>/dev/null || cat "$b")"
  if [ "$new" != "$old" ]; then
    echo "$(date +%T) brightness $old -> $new"
    old="$new"
  fi
  sleep 0.1
done

[o5gmmob8]

1. systemd
2. wayland via sway

Yes, xbacklight works.

I will check the above and report back. I think that is a good call with permissions or groups.

[o5gmmob8]

Good call, somehow, my user was no longer part of the video group or wheel.

I still see ACPI errors, but I suppose I can ignore those? The buttons work now.

[turtles]

Good call, somehow, my user was no longer part of the video group or wheel.

I still see ACPI errors, but I suppose I can ignore those? The buttons work now.

Glad you got it fixed, the ACPI can always be improved, but I don't think those errors are affecting you.