Public bug reported:
## Summary
After upgrading Ubuntu 26.04 LTS from kernel 7.0.0-27 to 7.0.0-28, the
internal display maximum brightness is significantly reduced
(approximately 50% of the expected brightness).
The brightness slider works normally, but even at 100%, the display is
much dimmer than before.
Booting the previous kernel (7.0.0-27) immediately restores full
brightness.
Windows 11 on the same machine also reaches full brightness, confirming
this is a Linux kernel regression rather than a hardware issue.
## Hardware
Laptop:
Dell Latitude 5421
GPU:
Intel Tiger Lake-H GT1 UHD Graphics
PCI:
00:02.0 VGA compatible controller: Intel Corporation TigerLake-H GT1 [UHD
Graphics] (rev 01)
Ubuntu:
26.04 LTS
Affected kernel:
7.0.0-28-generic
Working kernel:
7.0.0-27-generic
Display:
Internal eDP panel
Backlight driver:
/sys/class/backlight/intel_backlight
brightness:
1023
max_brightness:
1023
## Expected Result
Maximum brightness should match previous kernel versions and Windows.
## Actual Result
Maximum brightness is approximately half of normal.
## Regression
Works:
7.0.0-27-generic
Fails:
7.0.0-28-generic
Regression confirmed by rebooting between both kernels.
## Additional Information
No errors appear in dmesg related to i915 or backlight.
Wayland session.
Windows 11 on the same hardware is unaffected.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2162614
Title:
Dell Latitude 5421: Intel Tiger Lake backlight brightness reduced by
~50% after upgrading from kernel 7.0.0-27 to 7.0.0-28
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