https://bugs.kde.org/show_bug.cgi?id=520768
Bug ID: 520768
Summary: Software brightness control has no visual effect on
AMD Phoenix iGPU (Ryzen 8600G) + HDMI on Wayland
Classification: Plasma
Product: kwin
Version First 6.6.5
Reported In:
Platform: CachyOS
OS: Linux
Status: REPORTED
Severity: major
Priority: NOR
Component: colour-management
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
## Environment
- KDE Plasma: 6.6.5
- KWin: 6.6.5
- Kernel: 7.0.10-1-cachyos (CachyOS)
- GPU: AMD Ryzen 5 8600G integrated Radeon 760M (Phoenix/Hawk Point)
- Display: External monitor via HDMI (card1-HDMI-A-1)
- Display server: Wayland (KWin)
- amdgpu.dc: -1 (auto, DC enabled)
## Problem
Software brightness control via kscreen-doctor has no visual effect on the
display. Commands are accepted without error and kscreen-doctor reports the new
value, but the physical display brightness remains unchanged.
## Reproduction
```
kscreen-doctor output.HDMI-A-1.brightness.5
```
kscreen-doctor confirms the change ("set to 5%") but the display does not dim.
Also tested via D-Bus:
```
qdbus6 org.kde.Solid.PowerManagement
/org/kde/Solid/PowerManagement/Actions/BrightnessControl
org.kde.Solid.PowerManagement.Actions.BrightnessControl.setBrightness 500
```
No visual effect.
## Error in journal
```
kwin_wayland: 0x3: GL_INVALID_VALUE in glTexSubImage2D(yoffset 0 + height 1052
> 1022)
```
KWin attempts to upload a gamma LUT texture of height 1052, but the OpenGL
driver reports a maximum of 1022, causing the color management pipeline to fail
silently. As a result brightness changes are accepted but never applied to the
output.
## Additional notes
- DDC/CI (via ddcutil) also does not work: the monitor (HDMI) accepts VCP set
commands and reports the new value via getvcp, but does not apply hardware
brightness changes.
- No /sys/class/backlight/ device exists (external monitor, no internal panel).
- powerdevil D-Bus BrightnessControl interface is active and returns values
(max 10000), but changes have no visual effect for the same reason.
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