Public bug reported:
After updating to kernel 7.0.0-28-generic on a Dell G5 laptop (hybrid
graphics setup), the display backlight drops to near-zero/unusable
brightness as soon as the display manager (GDM/login screen) loads.
During early boot (GRUB and initial splash screen), the screen
brightness remains normal. Rolling back to kernel 7.0.0-27-generic or
7.0.0-22-generic completely fixes the issue and restores full backlight
control.
Expected Behavior:
Display backlight should maintain normal brightness levels when transition to
GDM / desktop session occurs.
Actual Behavior:
Display backlight drops drastically to minimal output upon reaching GDM.
Steps to Reproduce:
Boot system using kernel 7.0.0-28-generic.
Wait for the boot sequence to transition from splash screen to GDM /
login screen.
Display brightness drops to near-zero.
System Information:
Hardware: Dell G5 Laptop
OS: Ubuntu 26.04
Affected Kernel: 7.0.0-28-generic (Regression)
Working Kernel: 7.0.0-27-generic / 7.0.0-22-generic
NVIDIA Driver Version: 595.71.05
Log Diagnostic Snippet (dmesg):
The kernel appears to register two competing ACPI video devices (GFX0 and
PEGP), creating conflicting backlight buses:
Plaintext
[ 0.228094] ACPI: [Firmware Bug]: BIOS _OSI(Linux) query ignored
[ 11.173678] ACPI: video: Video Device [GFX0] (multi-head: yes rom: no post:
no)
[ 11.191146] input: Video Bus as /devices/pci0000:00/acpi.video_bus.0/
[ 11.204954] ACPI: video: Video Device [PEGP] (multi-head: no rom: yes post:
no)
[ 11.205018] input: Video Bus as
/devices/pci0000:00/0000:00:01.0/acpi.video_bus.1/
Tested kernel parameters acpi_backlight=native and acpi_backlight=vendor, but
neither resolved the brightness drop at GDM initialization.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2161578
Title:
Lost Bright after install kernel 7.0.0-28-generic on a Dell G5
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