Public bug reported:
Expected behavior:
Screen brightness should adjust when moving the KDE Plasma brightness slider or
using hardware hotkeys / brightnessctl.
Current behavior:
Screen brightness is locked at 100% maximum physical backlight output on kernel
7.0.0-28-generic. Moving the slider in KDE or executing `brightnessctl set 50%`
updates the software value in the OS, but the actual screen panel brightness
does not change.
Regression details:
- Working version: Kernel 7.0.0-14-generic (brightness controls worked as
expected).
- Broken version: Kernel 7.0.0-28-generic.
Hardware specs:
- Laptop: LG Gram 16Z90SP-A.AD78P
- CPU: Intel Core Ultra 7 155H (Meteor Lake)
- Integrated GPU: Intel Arc Graphics
- Discrete GPU: NVIDIA GeForce RTX 3050 Laptop GPU
- OS: Kubuntu / Ubuntu Studio 26.04 LTS (KDE Plasma 6.6.5 on Wayland)
Kernel parameters tested (none fixed the issue):
- acpi_backlight=native
- acpi_backlight=vendor
- acpi_backlight=video
- i915.enable_dpcd_backlight=1
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: linux-image-7.0.0-28-generic 7.0.0-28.28
ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12
Uname: Linux 7.0.0-28-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: mrneutel 2509 F.... pipewire
mrneutel 2567 F.... wireplumber
/dev/snd/seq: mrneutel 2509 F.... pipewire
CasperMD5CheckResult: pass
CurrentDesktop: KDE
Date: Sun Jul 26 20:00:57 2026
InstallationDate: Installed on 2026-07-25 (1 days ago)
InstallationMedia: Ubuntu-Studio 26.04 "Resolute Raccoon" - Release amd64
(20260423.1)
MachineType: LG Electronics 16Z90SP-A.AD78P
ProcEnviron:
LANG=C.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=alacritty
XDG_RUNTIME_DIR=<set>
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-28-generic
root=UUID=7e941a57-45f2-4476-91b4-2a758712393f ro quiet splash
acpi_backlight=native preempt=full threadirqs rcu_nocbs=all
PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No
PulseAudio daemon running, or not running as session daemon.
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 02/23/2024
dmi.bios.release: 0.1
dmi.bios.vendor: Phoenix Technologies Ltd.
dmi.bios.version: M2ZI0440 X64
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: 16Z90SP
dmi.board.vendor: LG Electronics
dmi.board.version: FAB1
dmi.chassis.asset.tag: Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: LG Electronics
dmi.chassis.version: 0.1
dmi.ec.firmware.release: 48.0
dmi.modalias:
dmi:bvnPhoenixTechnologiesLtd.:bvrM2ZI0440X64:bd02/23/2024:br0.1:efr48.0:svnLGElectronics:pn16Z90SP-A.AD78P:pvr0.1:rvnLGElectronics:rn16Z90SP:rvrFAB1:cvnLGElectronics:ct10:cvr0.1:skuEVO:pfagramPC:
dmi.product.family: gram PC
dmi.product.name: 16Z90SP-A.AD78P
dmi.product.sku: EVO
dmi.product.version: 0.1
dmi.sys.vendor: LG Electronics
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
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https://bugs.launchpad.net/bugs/2161846
Title:
[Regression] Backlight brightness stuck at 100% on LG Gram with Intel
Core Ultra 7 155H (kernel 7.0.0-28)
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