Reading this bug-report the issue seems to be that dell-uart-backlight is non-functional in the 6.5.y kernels and completely missing in the 24.04 6.8.y kernels. While in Ubuntu 23.04 with its 6.2 kernel dell- uart-backlight is present and functional.
The problem is that Canonical / Ubuntu wrote the original dell-uart- backlight driver but the way it accessed the serial port was rather hacky so it was never accepted upstream and it seems that when rebasing to a new kernel Ubuntu dropped their downstream patch (after it broken in 6.5.y ?). After I received the first bug reports about backlight issues on Dell AIO systems a few months ago I have re-written the dell-uart-backlight driver and submitted it upstream, this new rewrite was accepted upstream in kernel 6.10 . So I expect that backlight control will start working again for you if you upgrade to kernel 6.10 or newer. I'm not an Ubuntu user myself, but there are unmodified mainline kernels available for Ubuntu which allow you to update to 6.10.y without waiting for Ubuntu to move to this kernel version. Here are some docs on this: https://itsfoss.com/upgrade-linux-kernel-ubuntu/ https://wiki.ubuntu.com/Kernel/MainlineBuilds -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/2067498 Title: Can't control display backlight in 24.04 on Dell AIO system Status in linux package in Ubuntu: Confirmed Bug description: Ubuntu 23.10/24.04 Dell Inspiron 7700 AIO 6.5.0-35-generic/6.8.0-31-generic X11 https://askubuntu.com/questions/1514988/backlight-brightness-not- working-in-ubuntu-23-10-24-04-on-dell-7700-aio lsb_release -rd No LSB modules are available. Description: Ubuntu 24.04 LTS Release: 24.04 dell-uart-backlight kernel driver isn't in the 24.04 distribution, so NO Dell AIO display backlights can be adjusted. No brightness slider appears. (dell-uart-backlight is in the 23.10 distribution, but backlight/brightness slider control doesn't work 100% properly). Works fine in 23.04. ls -alR /lib/modules/6.5.0-35-generic/ | grep dell -rw-r--r-- 1 root root 13689 Apr 26 02:32 dell-smm-hwmon.ko.zst drwxr-xr-x 3 root root 4096 May 15 19:10 dell /lib/modules/6.5.0-35-generic/kernel/drivers/platform/x86/dell: -rw-r--r-- 1 root root 18647 Apr 26 02:32 dell-laptop.ko.zst -rw-r--r-- 1 root root 6158 Apr 26 02:32 dell-rbtn.ko.zst -rw-r--r-- 1 root root 8431 Apr 26 02:32 dell_rbu.ko.zst -rw-r--r-- 1 root root 13963 Apr 26 02:32 dell-smbios.ko.zst -rw-r--r-- 1 root root 4432 Apr 26 02:32 dell-smo8800.ko.zst -rw-r--r-- 1 root root 7762 Apr 26 02:32 dell-uart-backlight.ko.zst -rw-r--r-- 1 root root 3799 Apr 26 02:32 dell-wmi-aio.ko.zst -rw-r--r-- 1 root root 9209 Apr 26 02:32 dell-wmi-ddv.ko.zst -rw-r--r-- 1 root root 4532 Apr 26 02:32 dell-wmi-descriptor.ko.zst -rw-r--r-- 1 root root 11198 Apr 26 02:32 dell-wmi.ko.zst -rw-r--r-- 1 root root 3115 Apr 26 02:32 dell-wmi-led.ko.zst drwxr-xr-x 2 root root 4096 May 15 19:10 dell-wmi-sysman /lib/modules/6.5.0-35-generic/kernel/drivers/platform/x86/dell/dell-wmi-sysman: -rw-r--r-- 1 root root 18312 Apr 26 02:32 dell-wmi-sysman.ko.zst ls -alR /lib/modules/6.8.0-31-generic/ | grep dell -rw-r--r-- 1 root root 15140 Apr 19 14:46 dell-smm-hwmon.ko.zst drwxr-xr-x 3 root root 4096 May 25 10:15 dell /lib/modules/6.8.0-31-generic/kernel/drivers/platform/x86/dell: -rw-r--r-- 1 root root 18629 Apr 19 14:46 dell-laptop.ko.zst -rw-r--r-- 1 root root 6180 Apr 19 14:46 dell-rbtn.ko.zst -rw-r--r-- 1 root root 8582 Apr 19 14:46 dell_rbu.ko.zst -rw-r--r-- 1 root root 14726 Apr 19 14:46 dell-smbios.ko.zst -rw-r--r-- 1 root root 4433 Apr 19 14:46 dell-smo8800.ko.zst -rw-r--r-- 1 root root 3790 Apr 19 14:46 dell-wmi-aio.ko.zst -rw-r--r-- 1 root root 9166 Apr 19 14:46 dell-wmi-ddv.ko.zst -rw-r--r-- 1 root root 4492 Apr 19 14:46 dell-wmi-descriptor.ko.zst -rw-r--r-- 1 root root 11306 Apr 19 14:46 dell-wmi.ko.zst -rw-r--r-- 1 root root 3108 Apr 19 14:46 dell-wmi-led.ko.zst drwxr-xr-x 2 root root 4096 May 25 10:15 dell-wmi-sysman /lib/modules/6.8.0-31-generic/kernel/drivers/platform/x86/dell/dell-wmi-sysman: -rw-r--r-- 1 root root 18307 Apr 19 14:46 dell-wmi-sysman.ko.zst dup: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2067497 ProblemType: Bug DistroRelease: Ubuntu 24.04 Package: linux-image-6.8.0-31-generic 6.8.0-31.31 ProcVersionSignature: Ubuntu 6.8.0-31.31-generic 6.8.1 Uname: Linux 6.8.0-31-generic x86_64 NonfreeKernelModules: nvidia_modeset nvidia ApportVersion: 2.28.1-0ubuntu3 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/seq: al 3689 F.... pipewire /dev/snd/controlC1: al 3696 F.... wireplumber /dev/snd/controlC0: al 3696 F.... wireplumber CasperMD5CheckResult: pass CurrentDesktop: ubuntu:GNOME Date: Wed May 29 08:32:16 2024 InstallationDate: Installed on 2021-09-25 (978 days ago) InstallationMedia: Ubuntu 21.04 "Hirsute Hippo" - Release amd64 (20210420) MachineType: Dell Inc. Inspiron 7700 AIO 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-6.8.0-31-generic root=UUID=f0db2226-e28d-46dd-9b5a-457c87987ed2 ro quiet splash ipv6.disable=1 acpi_backlight=vendor acpi_osi=Linux vt.handoff=7 RelatedPackageVersions: linux-restricted-modules-6.8.0-31-generic N/A linux-backports-modules-6.8.0-31-generic N/A linux-firmware 20240318.git3b128b60-0ubuntu2 SourcePackage: linux UpgradeStatus: Upgraded to noble on 2024-05-25 (4 days ago) dmi.bios.date: 03/27/2024 dmi.bios.release: 1.28 dmi.bios.vendor: Dell Inc. dmi.bios.version: 1.28.0 dmi.board.name: 0K9T56 dmi.board.vendor: Dell Inc. dmi.board.version: A00 dmi.chassis.type: 13 dmi.chassis.vendor: Dell Inc. dmi.modalias: dmi:bvnDellInc.:bvr1.28.0:bd03/27/2024:br1.28:svnDellInc.:pnInspiron7700AIO:pvr:rvnDellInc.:rn0K9T56:rvrA00:cvnDellInc.:ct13:cvr:sku0A07: dmi.product.family: Inspiron dmi.product.name: Inspiron 7700 AIO dmi.product.sku: 0A07 dmi.sys.vendor: Dell Inc. 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