Kernel 6.5 breaks display brightness controls and sets it to 100% all the time

[Paddy Landau]

Since kernel 6.5, monitor brightness is set to 100%, and cannot be changed: The brightness controls have disappeared from Settings, and brightness doesn't respond to the keypad controls.

See the attached screenshot, showing the difference between the settings in kernels 6.2 and 6.5.

This applies to Ubuntu 22.04 and 23.10, whether using Wayland or X.Org.

It's possible (when using X.Org) to adjust the brightness with…

$ xrandr --output [monitor] --brightness [brightness]

e.g. on my machine…

$ xrandr --output eDP-1 --brightness 0.5

… but, unfortunately, it doesn't last long — anywhere between a less than a second later and about a minute later, the screen reverts to 100% brightness.

As a workaround, I am running the following command in the background…

$ while true; do xrandr --output eDP-1 --brightness 0.5; sleep 1s; done

… which results in the screen at the correct brightness, but frequently flashing!

———————
UPDATES
———————

• See comment #7 — This is somehow linked to the Night Light.
• Even when Night Light is permanently turned off, the screen still (sometimes; it's intermittent) goes bright when…
— Playing a video full screen (e.g. VLC, YouTube).
— Chrome gives a pop-up dialogue (e.g. downloading) or a notification (e.g. Calendar notification).

—————————
TESTED ON
—————————

• Ubuntu 22.04
— Kernel 6.2.0-39 and prior works correctly
— Kernels 6.5.0-14 & 6.5.0.15 have the problem

• Ubuntu 23.10
— Kernel 6.5.0-9 has the problem

$ sudo lshw -numeric -C display
  *-display
       description: VGA compatible controller
       product: CometLake-S GT2 [UHD Graphics 630] [8086:9BC5]
       vendor: Intel Corporation [8086]
       physical id: 2
       bus info: pci@0000:00:02.0
       logical name: /dev/fb0
       version: 05
       width: 64 bits
       clock: 33MHz
       capabilities: pciexpress msi pm vga_controller bus_master cap_list rom fb
       configuration: depth=32 driver=i915 latency=0 resolution=1920,1080
       resources: irq:145 memory:c1000000-c1ffffff memory:d0000000-dfffffff ioport:3000(size=64) memory:c0000-dffff

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: linux-image-6.5.0-14-generic 6.5.0-14.14~22.04.1
ProcVersionSignature: Ubuntu 6.5.0-14.14~22.04.1-generic 6.5.3
Uname: Linux 6.5.0-14-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.5
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Sat Jan 13 07:19:58 2024
InstallationDate: Installed on 2022-08-28 (502 days ago)
InstallationMedia: Ubuntu 22.04.1 LTS "Jammy Jellyfish" - Release amd64 (20220809.1)
SourcePackage: linux-signed-hwe-6.5
UpgradeStatus: No upgrade log present (probably fresh install)

[Paddy Landau (paddy-landau)]

I have been pointed to bug #2032174. It says that it has been fixed and ported to Jammy (22.04), but it seems that this is incorrect.

It is probably relevant to indicate my hardware, which is Dell OptiPlex 5480 All-In-One.
And my kernel is linux-signed-hwe-6.5, so maybe it wasn't ported to the HWE version?

[Paddy Landau (paddy-landau)]

Latest information seems to suggest that this isn't specifically to do with Dell (as per bug #2032174) but maybe to do with the Intel 6nn GPU.

In this thread from Ubuntu Forums, @MAFoElffen has this same problem with Intel 630, as I do:
https://ubuntuforums.org/showthread.php?t=2494260

[Launchpad Janitor (janitor)]

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

[Mike Ferreira (mafoelffen)]

I believe, as pointed out in https://bugs.launchpad.net/bugs/2032174 , it has to do with kernel 6.5, source package 'linux'. & source package 'linux-oem-6.5' ... This seems similar, yet a different problem.

It was there for the 6.2.0 series of kernels, but disappeared last week when the HWE stack went to 6.5.0 series kernels.

I have similar hardware than the reporter.

[Paddy Landau (paddy-landau)]

Further information:

I am using "xrandr --brightness …" in a background script that repeats every third of a second, to keep the brightness where I need it whenever the system resets it to 100%.

I've noticed that the system resets the brightness *exactly* every 60 seconds, with five resets over five seconds (the screen flashes each time before my script resets it). The resets aren't equally timed, but they always follow the same consistent pattern.

However, the system sometimes leaves the brightness alone for a longer period before reverting to resetting each minute.

I would love to be able to help by diagnosing what is causing that weird behaviour. The problem is that I have no clue whatsoever where to start.

[Paddy Landau (paddy-landau)]

Update:

This appears to be linked to the Night Light.

When Night Light is off:

• The brightness stays at whatever I set it to with xrandr. But, the computer still boots at 100% brightness, and missing the brightness controls.

When Night Light is on:

• The brightness resets to 100% every 60 seconds exactly, and for a few seconds after that according to a consistent pattern.

Interestingly, whenever I manually turn the Night Light on or off, the brightness immediately resets to 100%.