Dell XPS 13 (7390) brightness is not adjustable with recent kernel update

[Mathew Robinson]

uname -a shows:

Linux rocinante 5.4.0-1002-oem #4-Ubuntu SMP Wed Jan 15 10:44:42 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

I believe this bug is related to https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1862835 and https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1858844

This was broken then began working with kernel 5.4.0-18 however it is now broken again.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.4.0-1002-oem 5.4.0-1002.4
ProcVersionSignature: Ubuntu 5.4.0-1002.4-oem 5.4.8
Uname: Linux 5.4.0-1002-oem x86_64
ApportVersion: 2.20.11-0ubuntu24
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: chasinglogic 17213 F.... pulseaudio
CurrentDesktop: ubuntu:GNOME
Date: Tue Apr 7 09:55:19 2020
InstallationDate: Installed on 2020-04-06 (1 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Beta amd64 (20200402)
MachineType: Dell Inc. XPS 13 7390
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-1002-oem root=UUID=bf15f889-42e1-4e25-b73e-4b05806483ae ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-5.4.0-1002-oem N/A
 linux-backports-modules-5.4.0-1002-oem N/A
 linux-firmware 1.187
SourcePackage: linux-oem-5.4
UpgradeStatus: No upgrade log present (probably fresh install)
WifiSyslog:

dmi.bios.date: 11/25/2019
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.4.0
dmi.board.name: 0377MH
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 10
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr1.4.0:bd11/25/2019:svnDellInc.:pnXPS137390:pvr:rvnDellInc.:rn0377MH:rvrA00:cvnDellInc.:ct10:cvr:
dmi.product.family: XPS
dmi.product.name: XPS 13 7390
dmi.product.sku: 0962
dmi.sys.vendor: Dell Inc.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Lothar Braun (constcast)]

Same problem here. I cannot adjust the brightness using the GUI controls or the intel_backlight controls in /sys. The following action has (almost) no effect to the brightness or the value exposed in "actual_brightness" in /sys/class/backlight/intel_backlight:

echo $value /sys/class/backlight/intel_backlight/brightness

Example no change by running the following commands as root:

echo 1 > /sys/class/backlight/intel_backlight/brightness
echo `cat /sys/class/backlight/intel_backlight/max_brightness` > /sys/class/backlight/intel_backlight/brightness

The only difference that can be observed is when writing 0 to the file:

echo 0 > /sys/class/backlight/intel_backlight/brightness

This turns off the display.

The bug does not exist in linux-image-5.4.0-21-generic, so installing the standard non-oem kernel is a workaround to the bug.

[Timo Aaltonen (tjaalton)]

oem-5.4 is dead, so if the stock focal kernel works then that's enough, but you could also check that oem-5.6 doesn't regress..

[Lothar Braun (constcast)]

I performed a test with linux-image-5.6.0-1007-oem from focal-proposed. The brightness control works without problem on that version. So the problem seems to be fixed on linux-oem-5.6.

Is the version going to make it to the focal release?

[Mathew Robinson (mathew-robinson)]

linux-oem-5.6 resolves this issue for me.

[Timo Aaltonen (tjaalton)]

It's in focal now