Public bug reported:
Summary
After upgrading to Linux kernel 7.0.0-28-generic on Ubuntu 26.04 LTS,
the internal display backlight no longer responds to brightness changes
on an HP ZBook Studio G4.
The brightness slider and keyboard brightness keys update the kernel
backlight values correctly, but the LCD brightness remains unchanged.
Booting the same installation with Linux 7.0.0-14-generic restores
normal brightness control immediately.
System Information
Laptop
HP ZBook Studio G4
BIOS: P71 Ver. 01.45 (12/15/2022)
CPU
Intel Core i7-7820HQ (Kaby Lake)
Integrated GPU
Intel HD Graphics 630
Discrete GPU
NVIDIA Quadro M1200 4 GB
Operating System
Ubuntu 26.04 LTS
GNOME 50
Wayland
Working Kernel
Linux 7.0.0-14-generic
Brightness works normally.
Broken Kernel
Linux 7.0.0-28-generic
Symptoms:
Brightness slider moves
Brightness hotkeys function
/sys/class/backlight/intel_backlight/brightness changes
/sys/class/backlight/intel_backlight/actual_brightness changes
LCD panel brightness never changes
Diagnostics Performed
Confirmed:
Internal display driven by Intel i915
intel_backlight interface exists
Intel HD 630 detected correctly
Windows brightness control works
Ubuntu Live USB brightness works
Same BIOS
Same hardware
Same Ubuntu release
The issue occurs only after booting Linux 7.0.0-28.
Additional Notes
Removing the NVIDIA proprietary driver does not resolve the issue.
Booting the exact same installation using Linux 7.0.0-14 immediately
restores brightness control without any other changes.
This appears to be a kernel regression affecting Intel backlight
handling on HP ZBook Studio G4 systems.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: linux-image-7.0.0-14-generic 7.0.0-14.14
ProcVersionSignature: Ubuntu 7.0.0-14.14-generic 7.0.0
Uname: Linux 7.0.0-14-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: ifeoluwa 3539 F.... wireplumber
/dev/snd/controlC1: ifeoluwa 3539 F.... wireplumber
/dev/snd/seq: ifeoluwa 3533 F.... pipewire
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Thu Jul 30 22:03:09 2026
InstallationDate: Installed on 2026-07-29 (1 days ago)
InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1)
Lsusb:
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 04f2:b595 Chicony Electronics Co., Ltd HP HD Camera
Bus 001 Device 003: ID 138a:003f Validity Sensors, Inc. VFS495 Fingerprint
Reader
Bus 001 Device 004: ID 8087:0a2b Intel Corp. Bluetooth wireless interface
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
MachineType: HP HP ZBook Studio G4
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-14-generic
root=UUID=d2260859-0793-4b8d-91f7-341afa2a0601 ro quiet splash
crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 12/15/2022
dmi.bios.release: 1.45
dmi.bios.vendor: HP
dmi.bios.version: P71 Ver. 01.45
dmi.board.name: 826B
dmi.board.vendor: HP
dmi.board.version: KBC Version 47.80
dmi.chassis.type: 10
dmi.chassis.vendor: HP
dmi.ec.firmware.release: 71.128
dmi.modalias:
dmi:bvnHP:bvrP71Ver.01.45:bd12/15/2022:br1.45:efr71.128:svnHP:pnHPZBookStudioG4:pvr:rvnHP:rn826B:rvrKBCVersion47.80:cvnHP:ct10:cvr:sku3UJ13UC:pfa103C_5336ANHPZBookStudio:
dmi.product.family: 103C_5336AN HP ZBook Studio
dmi.product.name: HP ZBook Studio G4
dmi.product.sku: 3UJ13UC
dmi.sys.vendor: HP
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
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https://bugs.launchpad.net/bugs/2162386
Title:
Brightness/backlight regression on HP ZBook Studio G4 (Kaby Lake):
works on Linux 7.0.0-14 but fails on 7.0.0-28
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