Public bug reported:
After upgrading to Ubuntu 26.04 (kernel 7.0.0-generic), screen
brightness can no longer be changed on a Dell XPS 13 Plus (9320)
developer edition with the UHD+ 3840x2400 LCD panel (Alder Lake-P /
Raptor Lake-P graphics, device ID a7a0, i915 driver).
The GNOME brightness OSD appears and the slider moves, and the sysfs
interface accepts values, but the panel brightness does not actually
change.
This is a regression: booting the previously installed 6.17.0-35-generic
kernel on the same system, brightness control works normally. Kernels
7.0.0-28-generic and 7.0.0-29-generic are both affected.
## Symptoms / evidence
- /sys/class/backlight contains only intel_backlight (no acpi_video0).
- Writes to /sys/class/backlight/intel_backlight/brightness are accepted; both
`brightness` and `actual_brightness` track the written value (max_brightness =
1023), but the panel does not change.
- brightnessctl and the GNOME slider show the same behavior: values change,
panel does not.
- dmesg contains no backlight/PWM/panel errors at all. The only i915 anomaly
is: `i915 0000:00:02.0: [drm] Selective fetch area calculation failed in pipe A`
- Brightness set in the firmware setup (BIOS) works and persists into the 7.0.0
session, so the backlight hardware itself is functional; the OS just cannot
drive it.
- Brightness set while booted into 6.17.0-35 also persists into a subsequent
7.0.0 boot.
## Ruled out
- i915.enable_psr=0: verified active via
/sys/kernel/debug/dri/1/eDP-1/i915_psr_status (PSR mode: disabled). No effect
on the bug. (With defaults, PSR2 is enabled and the panel sits in DEEP_SLEEP.)
- i915.enable_dpcd_backlight=3: verified active via
/sys/module/i915/parameters/enable_dpcd_backlight. No effect; max_brightness
stayed at 1023, so the driver remained on the PWM path. This suggests the panel
is PWM-dimmed and the regression is in the PWM backlight path.
- Firmware is current (fwupd reports no pending updates).
- Kernel driver in use is i915 (not xe).
## Regression window
- Works: 6.17.0-35-generic (Ubuntu 25.10 kernel)
- Broken: 7.0.0-28-generic, 7.0.0-29-generic (Ubuntu 26.04)
## Hardware
- Dell XPS 13 Plus 9320, UHD+ 3840x2400 LCD (eDP-1), touch
- Intel Alder Lake-P/Raptor Lake-P integrated graphics, device ID a7a0, display
version 13.00 stepping E0
- Wayland session (GNOME), Secure Boot enabled (kernel lockdown: integrity)
## Workaround
Boot 6.17.0-35 (or enter BIOS setup) to set a brightness level, which
then persists into 7.0.0 sessions; brightness is otherwise fixed at that
level.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2163601
Title:
Regression: i915 backlight control broken on Dell XPS 13 Plus (9320,
UHD+ panel) with kernel 7.0.0, worked on 6.17.0
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