Public bug reported:
**Title**
Regression: Intel TigerLake eDP backlight broken after Linux 7.0.0-27 on
Dell Latitude 5420
---
### Hardware
* Laptop: Dell Latitude 5420
* BIOS: 1.54.1
* GPU: Intel TigerLake (i915)
* Internal display: AU Optronics eDP panel
* External display: Lenovo T2254pC (HDMI)
---
### Kernel versions
Working:
```
7.0.0-27-generic
```
Broken:
```
7.0.0-28-generic
```
---
### Description
After upgrading from kernel 7.0.0-27 to 7.0.0-28, the internal laptop
display brightness can no longer be controlled.
The GNOME brightness slider still moves normally, but the panel
brightness does not change.
The external HDMI monitor continues to work normally.
Booting back into kernel 7.0.0-27 immediately restores normal brightness
control.
This makes the issue appear to be a kernel regression.
---
### Working kernel
```
$ cat /sys/class/backlight/intel_backlight/max_brightness
96000
$ cat /sys/class/backlight/intel_backlight/brightness
96000
$ cat /sys/class/backlight/intel_backlight/actual_brightness
96000
```
Brightness changes correctly.
---
### Broken kernel
```
$ cat /sys/class/backlight/intel_backlight/max_brightness
1023
$ cat /sys/class/backlight/intel_backlight/brightness
1023
$ cat /sys/class/backlight/intel_backlight/actual_brightness
1023
```
Changing the brightness slider updates these values between 10 and 1023,
but the physical panel brightness never changes.
---
### Additional information
The internal panel is detected correctly.
PSR is disabled:
```
PSR mode: disabled
```
The issue occurs only after updating to kernel 7.0.0-28.
Rolling back to kernel 7.0.0-27 restores full functionality immediately
without any other changes.
This looks like a regression in Intel i915 eDP backlight handling.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: linux-image-7.0.0-28-generic 7.0.0-28.28
ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12
Uname: Linux 7.0.0-28-generic x86_64
ApportVersion: 2.34.0-0ubuntu2
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: ali-masroori 4129 F.... wireplumber
/dev/snd/seq: ali-masroori 4113 F.... pipewire
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Fri Jul 17 17:22:16 2026
InstallationDate: Installed on 2026-05-30 (48 days ago)
InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1)
MachineType: Dell Inc. Latitude 5420
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-28-generic
root=UUID=483412b7-bd4f-4bbc-81f0-7ea79150a588 ro quiet splash
i915.enable_dpcd_backlight=0
crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M
PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No
PulseAudio daemon running, or not running as session daemon.
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 04/23/2026
dmi.bios.release: 1.54
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.54.1
dmi.board.name: 01M3M4
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 10
dmi.chassis.vendor: Dell Inc.
dmi.modalias:
dmi:bvnDellInc.:bvr1.54.1:bd04/23/2026:br1.54:svnDellInc.:pnLatitude5420:pvr:rvnDellInc.:rn01M3M4:rvrA00:cvnDellInc.:ct10:cvr:sku0A20:pfaLatitude:
dmi.product.family: Latitude
dmi.product.name: Latitude 5420
dmi.product.sku: 0A20
dmi.sys.vendor: Dell Inc.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
--
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https://bugs.launchpad.net/bugs/2161102
Title:
Regression: Intel TigerLake eDP backlight broken after Linux 7.0.0-27
(Dell Latitude 5420)
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