Public bug reported:
## Summary
Display brightness control is nonfunctional on Linux Mint when running
kernel `7.0.0-30-generic` on an MSI GF63 8RD with Intel UHD Graphics
630.
The kernel exposes the `intel_backlight` interface normally, and writes
to the interface successfully update both `brightness` and
`actual_brightness`. However, these changes are not applied to the
physical display backlight, which remains at maximum brightness.
Booting the same installation with kernel `6.14.0-37-generic`
immediately restores normal brightness control.
## Hardware
- **Laptop:** MSI GF63 8RD
- **Integrated GPU:** Intel CoffeeLake-H GT2 [UHD Graphics 630]
- **iGPU driver:** `i915`
- **Discrete GPU:** NVIDIA GeForce GTX 1050 Ti Max-Q
- **NVIDIA driver:** `580.178.04`
- **Internal display:** eDP
- **Session:** X11
## Software
- **Distribution:** Linux Mint 22.3 Cinnamon
- **Affected kernel:** `7.0.0-30-generic`
- **Known-good kernel:** `6.14.0-37-generic`
## Steps to Reproduce
1. Boot Linux Mint using kernel `7.0.0-30-generic`.
2. Attempt to change display brightness using Cinnamon's brightness controls.
3. Observe that the displayed brightness setting changes, but physical screen
brightness does not.
4. Alternatively, bypass userspace and directly change the backlight through
sysfs:
```bash
echo 500 | sudo tee /sys/class/backlight/intel_backlight/brightness
```
5. Read the resulting values:
```bash
cat
/sys/class/backlight/intel_backlight/{brightness,actual_brightness,max_brightness}
```
The kernel reports:
```text
brightness:500
actual_brightness:500
max_brightness:1023
```
Despite this, the physical panel remains at maximum brightness.
6. Reboot and select:
```text
Advanced options for Linux Mint
→ Linux Mint, with Linux 6.14.0-37-generic
```
7. Brightness control now works normally on the same hardware and Linux
Mint installation.
## Backlight Interface on Affected Kernel
```text
/sys/class/backlight/intel_backlight
```
The device resolves to:
```text
../../devices/pci0000:00/0000:00:02.0/drm/card1/card1-eDP-1/intel_backlight
```
Properties before testing:
```text
brightness:1023
actual_brightness:1023
max_brightness:1023
type:raw
```
After writing `500`:
```text
brightness:500
actual_brightness:500
max_brightness:1023
type:raw
```
Again, the physical backlight does not change.
## Relevant ACPI Output
```text
ACPI: video: Video Device [GFX0] (multi-head: yes rom: no post: no)
input: Video Bus as /devices/pci0000:00/acpi.video_bus.0/input/input9
ACPI: video: Video Device [PEGP] (multi-head: no rom: yes post: no)
input: Video Bus as
/devices/pci0000:00/0000:00:01.0/acpi.video_bus.1/input/input10
```
The `video` and `msi_wmi` modules are loaded. Loading `video` explicitly
does not expose an additional ACPI backlight device;
`/sys/class/backlight/` continues to contain only `intel_backlight`.
## Expected Behavior
Changing the brightness setting should alter the physical backlight
intensity, as it does under kernel `6.14.0-37-generic`.
## Actual Behavior
Under `7.0.0-30-generic`, the kernel accepts brightness changes and
reports the requested value through both `brightness` and
`actual_brightness`, but the physical display remains at maximum
brightness.
## Regression
This appears to be a kernel regression.
The exact same Linux Mint installation and hardware behave as follows:
```text
6.14.0-37-generic → brightness works
7.0.0-30-generic → brightness values change, physical backlight does not
```
No userspace or hardware changes are required to reproduce or resolve
the issue; selecting the older kernel at boot is sufficient.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2164918
Title:
Linux 7.0.0-30 i915 Backlight Regression on MSI GF63 8RD
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