Public bug reported:
Hardware:
* Dell XPS 13 9340
* BIOS/firmware version: 1.24.0
* GPU: Intel Meteor Lake-P [Intel Arc Graphics], PCI ID 8086:7d55
* Kernel driver: i915
* Internal display: Sharp SHP 5519, Dell C71M1, 2560×1600 QHD+ LED-backlit LCD
* 64 GiB RAM
Software:
* Ubuntu 26.04.1 LTS, 64-bit
* GNOME 50
* Wayland
* Kernel 7.0.0-30-generic
Expected behaviour:
Changing brightness with the keyboard brightness keys or GNOME brightness
slider should change the physical brightness of the internal display.
Actual behaviour:
The brightness OSD appears and its slider changes, but the physical brightness
of the display remains completely unchanged.
Additional tests:
1. /sys/class/backlight/intel_backlight exists.
2. The interface reports max_brightness=1023 and type=raw.
3. Writing a value directly to /sys/class/backlight/intel_backlight/brightness
changes both brightness and actual_brightness, but the physical display
brightness remains unchanged.
4. For example, after writing 300, both brightness and actual_brightness
reported 300, while the display remained visually identical.
5. Brightness adjustment works correctly inside the Dell BIOS, so the panel and
backlight hardware are functional.
6. The issue also occurs with kernel 7.0.0-29-generic.
7. The following i915 DPCD backlight modes were tested without success:
* i915.enable_dpcd_backlight=1
* i915.enable_dpcd_backlight=2
* i915.enable_dpcd_backlight=3
8. The original boot configuration has been restored to
i915.enable_dpcd_backlight=1.
The issue therefore appears to be in the i915 backlight control for this
specific Sharp/Dell panel: the sysfs values change, but the
corresponding hardware brightness command is not applied.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: linux-image-7.0.0-30-generic 7.0.0-30.30
ProcVersionSignature: Ubuntu 7.0.0-30.30-generic 7.0.12
Uname: Linux 7.0.0-30-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: armando 6199 F.... pipewire
armando 6209 F.... wireplumber
/dev/snd/seq: armando 6199 F.... pipewire
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Fri Sep 4 18:43:49 2026
InstallationDate: Installed on 2026-06-05 (91 days ago)
InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1)
MachineType: Dell Inc. XPS 13 9340
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=/vmlinuz-7.0.0-30-generic
root=/dev/mapper/ubuntu--vg-ubuntu--lv ro quiet splash xe.force_probe=7d14
i915.force_probe=!7d14 xe.fastboot=1 i915.enable_dpcd_backlight=1
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: 01/27/2026
dmi.bios.release: 1.24
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.24.0
dmi.board.name: 08214J
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 10
dmi.chassis.vendor: Dell Inc.
dmi.ec.firmware.release: 1.21
dmi.modalias:
dmi:bvnDellInc.:bvr1.24.0:bd01/27/2026:br1.24:efr1.21:svnDellInc.:pnXPS139340:pvr:rvnDellInc.:rn08214J:rvrA00:cvnDellInc.:ct10:cvr:sku0C87:pfaXPS:
dmi.product.family: XPS
dmi.product.name: XPS 13 9340
dmi.product.sku: 0C87
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/2166520
Title:
Dell XPS 13 9340: intel_backlight values change but Sharp C71M1 panel
brightness does not
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