Public bug reported:
On a Dell Inspiron 5480 (BIOS 2.18.0, 11/11/2022), display brightness
cannot be changed from the operating system through any available
backlight interface, while brightness control works correctly from the
BIOS setup screen itself.
Hardware:
Dell Inspiron 5480
Intel Core i7-8565U (Whiskey Lake-U), Intel UHD Graphics 620 + Nvidia GeForce
MX150 (hybrid graphics)
BIOS/UEFI 2.18.0 (11/11/2022), confirmed up to date via fwupdmgr / Dell Service
Tag lookup
Steps taken / diagnostics:
/sys/class/backlight/intel_backlight/brightness accepts writes without error,
but no visible change on screen.
Tested acpi_backlight=vendor → exposes dell_backlight instead of
intel_backlight. Writes via brightnessctl are accepted (confirmed by reading
back the value) but again produce no visible change.
Tested acpi_backlight=vendor i915.enable_dpcd_backlight=1 (DPCD path) → no
change.
Tested acpi_backlight=video video.use_native_backlight=0 → no change.
Tested on both installed kernels: 7.0.0-28-generic and 7.0.0-27-generic → same
behavior on both.
Tested from a plain TTY (Ctrl+Alt+F3, no GNOME/Wayland/X11 running) → still no
change, ruling out desktop environment / compositor involvement.
Removed the dell_laptop module (modprobe -r dell_laptop) → dell_backlight
device disappears entirely, no other screen-backlight device remains.
dmesg shows:
wmi_bus wmi_bus-PNP0C14:04: [Firmware Bug]: WQBC data block query control
method not found
Brightness changes normally when done from the BIOS setup screen (F2 at boot),
confirming the panel/EC hardware itself works correctly.
Expected behavior: Brightness should change when writing to the active
backlight sysfs interface, matching what F2/BIOS control achieves.
Actual behavior: All backlight sysfs interfaces (intel_backlight,
dell_backlight) accept writes silently but produce no physical change in
screen brightness.
Additional info: The [Firmware Bug]: WQBC data block query control
method not found message suggests the Dell WMI ACPI table on this system
is missing the method the kernel expects for backlight control, which
would explain why the OS-level requests never reach the embedded
controller/BIOS layer that actually drives the panel.
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: 2.34.1-0ubuntu0.1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: joelmo 4603 F.... wireplumber
/dev/snd/seq: joelmo 4596 F.... pipewire
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Wed Aug 5 20:51:51 2026
InstallationDate: Installed on 2026-01-19 (199 days ago)
InstallationMedia: Ubuntu 25.10 "Questing Quokka" - Release amd64 (20251007)
Lsusb:
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 046d:c52f Logitech, Inc. Nano Receiver
Bus 001 Device 003: ID 0c45:671b Microdia Integrated_Webcam_HD
Bus 001 Device 004: ID 8087:0aaa Intel Corp. Bluetooth 9460/9560 Jefferson
Peak (JfP)
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
MachineType: Dell Inc. Inspiron 5480
ProcEnviron:
LANG=pt_BR.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-28-generic
root=UUID=f584917d-e1ca-4059-866b-b80dce7c5238 ro quiet splash
acpi_backlight=video video.use_native_backlight=0
crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M
SourcePackage: linux
UpgradeStatus: Upgraded to resolute on 2026-04-24 (103 days ago)
dmi.bios.date: 11/11/2022
dmi.bios.release: 2.18
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 2.18.0
dmi.board.name: 07G539
dmi.board.vendor: Dell Inc.
dmi.board.version: A02
dmi.chassis.asset.tag: 28R57Z
dmi.chassis.type: 10
dmi.chassis.vendor: Dell Inc.
dmi.modalias:
dmi:bvnDellInc.:bvr2.18.0:bd11/11/2022:br2.18:svnDellInc.:pnInspiron5480:pvr:rvnDellInc.:rn07G539:rvrA02:cvnDellInc.:ct10:cvr:sku089C:pfaInspiron:
dmi.product.family: Inspiron
dmi.product.name: Inspiron 5480
dmi.product.sku: 089C
dmi.sys.vendor: Dell Inc.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute
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https://bugs.launchpad.net/bugs/2162937
Title:
Backlight brightness cannot be changed from OS on Dell Inspiron 5480
(WQBC WMI firmware bug)
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