[Bug 2161102] Re: Regression: Intel TigerLake eDP backlight broken after Linux 7.0.0-27 (Dell Latitude 5420)

Thanks for reporting the bug and providing the logs already! This issue looks to be much alike https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2161309, would you mind looking at comment #4 and #10 and possibly doing a few more checks? You'll need to revert any boot line params you have added and update grub to I can have a clear picture whether you are hitting exactly the same issue. Thanks! ** Changed in: linux (Ubuntu) Importance: Undecided => High ** Changed in: linux (Ubuntu) Assignee: (unassigned) => Krystian Kaniewski (kkaniewski) -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb https://bugs.launchpad.net/bugs/2161102 Title: Regression: Intel TigerLake eDP backlight broken after Linux 7.0.0-27 (Dell Latitude 5420) Status in linux package in Ubuntu: Confirmed Bug description: **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. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2161102/+subscriptions