Public bug reported:
After a routine system update that upgraded the kernel from 6.17.0-40-generic
to 7.0.0-28-generic (via linux-image-generic-hwe-24.04), the laptop's screen
brightness control stopped working entirely. This includes both the dedicated
keyboard brightness keys and the GUI brightness slider.
Symptoms:
Brightness hotkeys register correctly (on-screen indicator/slider moves as
expected)
/sys/class/backlight/intel_backlight/brightness and actual_brightness update
correctly when written to, including via direct root-level echo writes
Despite the above, the physical panel brightness does not change at all
xrandr --output eDP-1 --brightness also has no visible effect
dmesg shows hp_wmi: query 0x4 returned error 0x5 on boot
dmesg shows i915 0000:00:02.0: [drm] Skipping intel_backlight registration when
acpi_backlight=video is used
Troubleshooting already performed (no effect on any):
acpi_backlight=native, acpi_backlight=vendor, acpi_backlight=video
i915.enable_dpcd_backlight=0, i915.enable_dpcd_backlight=1,
i915.enable_dpcd_backlight=3
Confirmed video group membership and correct sysfs permissions
Confirmed no firmware/BIOS update occurred alongside the kernel update
(fwupdmgr get-history shows no history)
[Confirmed working / not yet tested] on kernel 6.17.0-40-generic — brightness
control [worked correctly / still broken] on the previous kernel, isolating
this to a kernel-level regression rather than a config or hardware issue.
Hardware:
HP EliteBook 840 G6 (or G7 — confirm your exact model), Intel Coffee Lake
integrated graphics (device ID 3ea0), coffeelake/ult display version 9.00
Kernel versions:
Broken: 7.0.0-28-generic
Working (if confirmed): 6.17.0-40-generic
ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: linux-image-7.0.0-28-generic 7.0.0-28.28~24.04.1
ProcVersionSignature: Ubuntu 6.17.0-40.40~24.04.1-generic 6.17.13
Uname: Linux 6.17.0-40-generic x86_64
ApportVersion: 2.28.2-0ubuntu0.1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: bam 3544 F.... pipewire
bam 3549 F.... wireplumber
/dev/snd/seq: bam 3544 F.... pipewire
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Fri Jul 17 15:06:32 2026
InstallationDate: Installed on 2026-02-05 (162 days ago)
InstallationMedia: Ubuntu 24.04.3 LTS "Noble Numbat" - Release amd64
(20250805.1)
MachineType: HP HP EliteBook 840 G6
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-6.17.0-40-generic
root=UUID=ebc90d0c-5e46-429b-b79e-d70ba70bd581 ro quiet splash vt.handoff=7
RelatedPackageVersions:
linux-restricted-modules-6.17.0-40-generic N/A
linux-backports-modules-6.17.0-40-generic N/A
linux-firmware 20240318.git3b128b60-0ubuntu2.27
SourcePackage: linux-hwe-7.0
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/02/2023
dmi.bios.release: 26.0
dmi.bios.vendor: HP
dmi.bios.version: R70 Ver. 01.26.00
dmi.board.name: 8549
dmi.board.vendor: HP
dmi.board.version: KBC Version 52.6F.00
dmi.chassis.type: 10
dmi.chassis.vendor: HP
dmi.ec.firmware.release: 82.111
dmi.modalias:
dmi:bvnHP:bvrR70Ver.01.26.00:bd10/02/2023:br26.0:efr82.111:svnHP:pnHPEliteBook840G6:pvrSBKPF:rvnHP:rn8549:rvrKBCVersion52.6F.00:cvnHP:ct10:cvr:sku8AG91US#ABA:
dmi.product.family: 103C_5336AN HP EliteBook
dmi.product.name: HP EliteBook 840 G6
dmi.product.sku: 8AG91US#ABA
dmi.product.version: SBKPF
dmi.sys.vendor: HP
** Affects: linux-hwe-7.0 (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug noble third-party-packages wayland-session
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Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/2161091
Title:
n i915 backlight regression on your Coffee Lake panel (device ID
3ea0), and reference that 6.17.0-40 works fine but 7.0.0-28 doesn't
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