Public bug reported:
# Bug report draft — for Launchpad (ubuntu-bug linux)
## Title
i915: backlight brightness writes have no physical effect on ASUS VivoBook
N580GD (X580GD) with kernel 7.0.0-28-generic — regression from 6.17
## Summary
After upgrading from linux-image-6.17.0-40-generic (HWE) to
linux-image-7.0.0-28-generic
(HWE, noble-updates) on Kubuntu 24.04.4, changing the display brightness stops
having any
physical effect. The panel stays at a fixed brightness level regardless of:
- fn+brightness hotkeys,
- the KDE Plasma brightness slider,
- direct writes to /sys/class/backlight/intel_backlight/brightness as root.
In all cases the sysfs value AND actual_brightness update normally and userspace
(PowerDevil/applet) tracks the change — but the physical panel backlight never
changes.
Booting back into 6.17.0-40-generic on the same system fully restores
brightness control.
## Hardware
- ASUS VivoBook_ASUSLaptop X580GD_N580GD (BIOS X580GD.322, 05/19/2020)
- Intel Core i7-8750H, UHD Graphics 630 (CoffeeLake-H GT2, 8086:3e9b) — desktop
renders on i915
- NVIDIA GTX 1050 Mobile (PRIME on-demand, nvidia-driver-580) — not involved:
issue
reproduces with the panel driven by i915; nvidia driver loaded in both kernels
- Internal eDP panel
## Observations / diagnostics done
1. `/sys/class/backlight/` contains only `intel_backlight` on both kernels.
2. On 7.0.0-28 the brightness scale changed: max_brightness = 1023
(on 6.17.0-40 the range is much larger, ~7500; systemd-backlight logged
"Saved brightness 3600 is too high; decreasing to 1023" on first 7.0 boot).
3. Writing any value (200 / 500 / 800) to intel_backlight/brightness as root:
value is accepted, actual_brightness follows, panel does NOT change. No
dmesg errors.
4. KDE PowerDevil DBus setBrightness works the same way — value tracked, no
physical change.
5. No relevant errors in dmesg/journal (no i915 warnings, no ACPI errors).
6. Suspicion: i915 in 7.0 may be picking the wrong backlight control method for
this eDP
panel (PWM pin vs DPCD aux). Not yet tested: booting 7.0 with
i915.enable_dpcd_backlight=0 / =1.
## Steps to reproduce
1. Boot linux-image-7.0.0-28-generic on ASUS N580GD/X580GD.
2. Press brightness hotkeys or `echo 200 | sudo tee
/sys/class/backlight/intel_backlight/brightness`.
3. Observe actual_brightness changes but the physical panel brightness does not.
## Workaround
Boot the previous HWE kernel 6.17.0-40-generic (brightness control fully
functional there).
## Version info
- Description: Ubuntu 24.04.4 LTS (Kubuntu), Plasma 5.27 X11 session
- Regression window: linux-hwe 6.17.0-40 (good) → 7.0.0-28 (bad), same userspace
ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: linux-image-7.0.0-28-generic 7.0.0-28.28~24.04.1
ProcVersionSignature: Ubuntu 7.0.0-28.28~24.04.1-generic 7.0.12
Uname: Linux 7.0.0-28-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.28.2-0ubuntu0.1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: vlad 1663 F.... wireplumber
/dev/snd/seq: vlad 1660 F.... pipewire
CRDA: N/A
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Sat Jul 18 12:36:42 2026
HibernationDevice: RESUME=none
InstallationDate: Installed on 2020-07-28 (2181 days ago)
InstallationMedia: Kubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
Lsusb:
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 13d3:56a2 IMC Networks USB2.0 HD UVC WebCam
Bus 001 Device 003: ID 0bda:0129 Realtek Semiconductor Corp. RTS5129 Card
Reader Controller
Bus 001 Device 004: ID 8087:0036 Intel Corp.
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
MachineType: ASUSTeK COMPUTER INC. VivoBook_ASUSLaptop X580GD_N580GD
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-7.0.0-28-generic
root=/dev/mapper/vgkubuntu-root ro quiet splash mitigations=off vt.handoff=7
PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No
PulseAudio daemon running, or not running as session daemon.
RelatedPackageVersions:
linux-restricted-modules-7.0.0-28-generic N/A
linux-backports-modules-7.0.0-28-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: 05/19/2020
dmi.bios.release: 5.13
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: X580GD.322
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: X580GD
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: 1.0
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK COMPUTER INC.
dmi.chassis.version: 1.0
dmi.modalias:
dmi:bvnAmericanMegatrendsInc.:bvrX580GD.322:bd05/19/2020:br5.13:svnASUSTeKCOMPUTERINC.:pnVivoBook_ASUSLaptopX580GD_N580GD:pvr1.0:rvnASUSTeKCOMPUTERINC.:rnX580GD:rvr1.0:cvnASUSTeKCOMPUTERINC.:ct10:cvr1.0:sku:pfaVivoBook:
dmi.product.family: VivoBook
dmi.product.name: VivoBook_ASUSLaptop X580GD_N580GD
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK COMPUTER INC.
** Affects: linux-hwe-7.0 (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug noble regression-update
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https://bugs.launchpad.net/bugs/2161183
Title:
i915: backlight brightness writes have no physical effect on ASUS
VivoBook N580GD (X580GD) with kernel 7.0.0-28-generic — regression
from 6.17
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