Public bug reported:
# Bug Report: Screen Brightness Control Non-Functional on Dell Latitude
5490 (Intel UHD 620 / i915)
## Summary
On a Dell Latitude 5490 with Intel UHD Graphics 620 (Kaby Lake-R), the screen
brightness slider and Fn brightness keys have no effect on actual screen
brightness. The backlight sysfs interface accepts and retains written values,
but the physical display never changes brightness. The same hardware works
correctly in Windows 10 (dual-boot), ruling out a hardware fault.
## System Information
- **Model:** Dell Latitude 5490
- **BIOS version:** 1.41.0
- **Graphics:** Intel Kaby Lake-R, UHD Graphics 620 (PCI device ID 5917),
driver `i915`
- **OS:** Ubuntu 26.04 LTS, dual-boot with Windows 10
- **Kernels tested:** `7.0.0-29-generic` (stock) and `6.17.x` (manually
installed mainline build) — issue identical on both
- **Desktop/session:** GNOME, default Wayland session
- **Only backlight device exposed:**
```
$ ls /sys/class/backlight/
intel_backlight
$ cat /sys/class/backlight/intel_backlight/max_brightness
1023
```
## Expected Behavior
Moving the brightness slider in Quick Settings, or pressing the Fn brightness
keys, should increase or decrease the physical screen brightness.
## Actual Behavior
- The slider does not visibly respond to input (appears to "float").
- Fn brightness keys have no effect.
- Manually writing to `/sys/class/backlight/intel_backlight/brightness` updates
and *retains* the value, but the physical panel brightness never visibly
changes.
## Steps to Reproduce
1. Fresh install of Ubuntu 26.04 LTS via dual-boot alongside Windows 10 on a
Dell Latitude 5490.
2. Log into the default GNOME (Wayland) session.
3. Attempt to adjust brightness via the Quick Settings slider or Fn+brightness
keys.
4. No change in screen brightness occurs.
## Troubleshooting Already Performed
**1. Confirmed the value is written and held (not being reset by another
process):**
```
$ sudo sh -c 'echo 1023 > /sys/class/backlight/intel_backlight/brightness'
$ for i in 1 2 3 4 5; do cat /sys/class/backlight/intel_backlight/brightness;
sleep 1; done
1023
1023
1023
1023
1023
```
No visible brightness change despite the value holding steady for 5+ seconds.
**2. Ruled out file permissions:**
- Added a udev rule granting the `video` group write access to the brightness
file.
- Confirmed user is a member of the `video` group.
- Confirmed resulting permissions: `-rw-rw-r-- 1 root video ... brightness`.
- No change in behavior.
**3. Tested multiple i915/ACPI backlight kernel parameters** (each tested
individually via GRUB):
- `acpi_backlight=vendor`
- `acpi_backlight=native`
- `acpi_backlight=video`
- `i915.enable_dpcd_backlight=1`
- `i915.enable_dpcd_backlight=3`
None resolved the issue.
**4. Tested an alternate kernel:** manually installed mainline kernel
`6.17.x` (via `.deb` packages from kernel.ubuntu.com), requiring Secure
Boot to be disabled in BIOS to boot the unsigned build. The issue is
identical on `6.17.x`, ruling out a regression isolated to the `7.0.0`
kernel series.
**5. Confirmed relevant Dell kernel modules are loaded:**
```
$ lsmod | grep dell
dell_pc, platform_profile, dell_rbtn, dell_laptop, dell_smm_hwmon,
dell_wmi, dell_smbios, dcdbas, dell_wmi_sysman, dell_wmi_descriptor,
dell_lis3lv02d, dell_smo8800, video
```
No separate Dell-specific backlight device is created — only `intel_backlight`
appears in `/sys/class/backlight/`.
**6. Confirmed GNOME's `gsd-power` and `gsd-color` daemons run
normally** and are not overwriting or resetting the brightness value.
**7. Checked `dmesg` for i915/panel/eDP-related errors:** the display
initializes cleanly —
```
i915 0000:00:02.0: [drm] Found kabylake (device ID 5917) integrated display
version 9.00 stepping C0
i915 0000:00:02.0: [drm] Finished loading DMC firmware i915/kbl_dmc_ver1_04.bin
(v1.4)
```
No explicit backlight/panel/DPCD/PWM error or warning messages are logged.
**8. Hardware ruled out entirely:** booting into Windows 10 on the same
physical machine, the brightness slider and Fn keys work correctly and
reliably. This confirms the panel, backlight hardware, and cabling are
all functioning correctly — the issue is isolated to Linux/i915 driver
behavior on this model.
## Additional Notes
- Issue has been present since the very first boot after installation (not a
regression from a later update on this machine).
- Willing to provide further debug output on request (e.g., `sudo acpidump`,
`intel_reg dump`, full `journalctl -b`, `sudo dmesg` in full).
## Suggested Tags
`i915` `backlight` `kaby-lake` `dell-latitude-5490` `brightness` `dual-boot`
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: xorg (not installed)
ProcVersionSignature: Ubuntu 7.0.0-29.29-generic 7.0.12
Uname: Linux 7.0.0-29-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Mon Aug 17 10:32:50 2026
InstallationDate: Installed on 2026-08-16 (1 days ago)
InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1)
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
SourcePackage: xorg
Symptom: display
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: xorg (Ubuntu)
Importance: Undecided
Status: New
** Tags: brightness not slider working
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https://bugs.launchpad.net/bugs/2163618
Title:
brightness slider is not increasing or decreasing brightness
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