[Bug 2150737] Re: M3800 keyboard backlight problem ubuntu 26.04

rom1@rom1-M3800:~$ lsmod | grep dell dell_laptop 40960 0 dell_wmi 28672 1 dell_laptop dell_smbios 36864 2 dell_wmi,dell_laptop dell_smm_hwmon 36864 0 dcdbas 24576 1 dell_smbios sparse_keymap 12288 1 dell_wmi dell_wmi_descriptor 20480 2 dell_wmi,dell_smbios dell_lis3lv02d 16384 0 dell_smo8800 16384 0 dell_rbtn 20480 0 video 77824 3 dell_wmi,dell_laptop,i915 wmi 36864 7 video,dell_wmi,wmi_bmof,dell_smm_hwmon,dell_smbios,dell_wmi_descriptor,mxm_wmi -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb https://bugs.launchpad.net/bugs/2150737 Title: M3800 keyboard backlight problem ubuntu 26.04 Status in linux package in Ubuntu: New Bug description: Hi, I have a bug related to the keyboard backlight of my DELL M3800. If I use FN + F10 key combinaison all is working good. If I try to use the gnome setting or kde setting, nothing happens. rom1@rom1-M3800:~$ ls /sys/class/leds dell::kbd_backlight input3::capslock input3::numlock input3::scrolllock phy0-led rom1@rom1-M3800:~$ cat /sys/class/leds/dell::kbd_backlight/brightness 0 rom1@rom1-M3800:~$ cat /sys/class/leds/dell::kbd_backlight/max_brightness 2 rom1@rom1-M3800:~$ cat /sys/class/leds/dell::kbd_backlight/trigger [none] usb-gadget usb-host rfkill-any rfkill-none kbd-scrolllock kbd-numlock kbd-capslock kbd-kanalock kbd-shiftlock kbd-altgrlock kbd-ctrllock kbd-altlock kbd-shiftllock kbd-shiftrlock kbd-ctrlllock kbd-ctrlrlock disk-activity disk-read disk-write mtd nand-disk cpu cpu0 cpu1 cpu2 cpu3 cpu4 cpu5 cpu6 cpu7 panic ACAD-online BAT1-charging-or-full BAT1-charging BAT1-full BAT1-charging-blink-full-solid BAT1-charging-orange-full-green mmc0 rc-feedback bluetooth-power hci0-power rfkill0 rfkill1 phy0rx phy0tx phy0assoc phy0radio rfkill2 If I use the key combinaison I can see the value of brightness move from 0 to 2 or 1 and physically the keyboard backlight works well. If I try to force the value to 2 in the brightness using command line, nothing happens and the value foes back to 0. I tried with Ubuntu 26.04, Kubuntu 26.04 and Fedora 44 gnome + kde. All have the same behaviour. When writing to /sys/class/leds/dell::kbd_backlight/brightness via echo, the command returns without error but the value immediately reverts to 0. The file permission show -rw-r--r-- 1 root root. The driver appears to silently reject writes from userspace while accepting them from the ACPI firmware via FN + F10. Could you please fix this ? Best regards. ProblemType: Bug DistroRelease: Ubuntu 26.04 Package: linux-image-7.0.0-15-generic 7.0.0-15.15 ProcVersionSignature: Ubuntu 7.0.0-15.15-generic 7.0.0 Uname: Linux 7.0.0-15-generic x86_64 ApportVersion: 2.34.0-0ubuntu2 Architecture: amd64 AudioDevicesInUse:  USER PID ACCESS COMMAND  /dev/snd/controlC1: rom1 3768 F.... wireplumber  /dev/snd/controlC0: rom1 3768 F.... wireplumber  /dev/snd/seq: rom1 3749 F.... pipewire CasperMD5CheckResult: pass CurrentDesktop: ubuntu:GNOME Date: Thu Apr 30 13:07:07 2026 InstallationDate: Installed on 2026-04-24 (6 days ago) InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1) MachineType: Dell Inc. Dell Precision M3800 ProcEnviron:  LANG=fr_FR.UTF-8  PATH=(custom, no user)  SHELL=/bin/bash  TERM=xterm-256color  XDG_RUNTIME_DIR=<set> ProcFB: 0 i915drmfb ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-15-generic root=UUID=1e291b4f-afed-45e8-ab4d-25bdbd06707a ro quiet splash crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M SourcePackage: linux UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 07/02/2020 dmi.bios.release: 65.14 dmi.bios.vendor: Dell Inc. dmi.bios.version: A14 dmi.board.name: Dell Precision M3800 dmi.board.vendor: Dell Inc. dmi.board.version: A14 dmi.chassis.type: 8 dmi.chassis.vendor: Dell Inc. dmi.chassis.version: Not Specified dmi.modalias: dmi:bvnDellInc.:bvrA14:bd07/02/2020:br65.14:svnDellInc.:pnDellPrecisionM3800:pvrA14:rvnDellInc.:rnDellPrecisionM3800:rvrA14:cvnDellInc.:ct8:cvrNotSpecified:skuDellPrecisionM3800:pfa: dmi.product.name: Dell Precision M3800 dmi.product.sku: Dell Precision M3800 dmi.product.version: A14 dmi.sys.vendor: Dell Inc. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2150737/+subscriptions