Public bug reported:
After a routine apt upgrade on 2026-07-21, the kernel was automatically
updated from 6.17.0-35-generic to 7.0.0-28-generic via
linux-image-generic-hwe-24.04.
Since then, screen brightness cannot be adjusted via GNOME slider or Fn keys.
Hardware: HP EliteBook 820 G2, Intel Broadwell CPU (2015), BIOS M71 Ver.
01.31
Diagnosis performed:
- /sys/class/backlight/intel_backlight exists, max_brightness=1023
- Writing to brightness file (even as root) succeeds and value persists
(verified via cat), but has no visible effect on the physical panel
- Confirmed via clean A/B boot test: brightness control works normally
on 6.17.0-35-generic, fails on 7.0.0-28-generic — same hardware,
same session, only kernel version differs
- Tested boot parameters acpi_backlight=native and acpi_backlight=vendor —
neither restored functionality
This appears related to Bug #2161102 (Intel TigerLake eDP backlight broken
after Linux 7.0.0-27), though that report concerns different Intel graphics
generation (TigerLake vs. Broadwell here) and different hardware (Dell vs HP),
so likely a related but distinct regression in the same kernel series.
Current workaround: pinned to 6.17.0-35-generic via GRUB_DEFAULT +
apt-mark hold on linux-image-7.0.0-28-generic and linux-image-generic-hwe-24.04.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2161562
Title:
Backlight control broken on HP EliteBook 820 G2 (Broadwell) after
upgrade to 7.0.0-28-generic
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