https://bugs.kde.org/show_bug.cgi?id=516668
Bug ID: 516668
Summary: Software brightness on external HDMI monitor
flickers/dims erratically during active use (Wayland,
AMD RX 6600)
Classification: Plasma
Product: kwin
Version First 6.5.5
Reported In:
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
===============================================================
KDE BUG REPORT — File at: https://bugs.kde.org/enter_bug.cgi
Product: kwin
Component: platforms/drm
===============================================================
TITLE:
Software brightness on external HDMI monitor flickers/dims erratically during
active use (Wayland, AMD RX 6600)
DESCRIPTION:
On a desktop system with an AMD RX 6600 connected to a Samsung TV via HDMI
(no DDC/CI support), the screen randomly dims and brightens. This happens
during active use — while typing and moving the mouse — not just during idle.
`kscreen-doctor -o` shows the brightness value dropping from 100% to ~60%
spontaneously, then returning to 100%. The effect is a visible flash/flicker.
The monitor does not support DDC/CI (`ddcutil` confirms "I2C slave address x37
is unresponsive"), so KDE is using software (SDR) brightness control. The
`kwinoutputconfig.json` has `allowSdrSoftwareBrightness: true` and
`colorPowerTradeoff: PreferEfficiency`.
Setting `DimDisplayIdleTimeoutSec=0` in `powerdevilrc` and disabling screen
locking has no effect. Disabling Night Color reduces but does not eliminate
the issue. The brightness continues to fluctuate even with all idle/dim
timeouts at 0.
Steps to reproduce:
1. Connect an external monitor via HDMI that does not support DDC/CI
2. Use the system normally (type, move mouse)
3. Observe random dimming flashes
Expected: Stable brightness at the configured level.
Actual: Brightness drops to ~60% erratically, then snaps back, causing
visible flashing.
Workaround (partial): Setting `allowSdrSoftwareBrightness: false` in
`kwinoutputconfig.json` helps, but KWin's running process overwrites the
file with its in-memory state.
System info:
- Plasma 6.5.5 / KWin 6.5.5
- Wayland session
- Nobara 43 (Fedora 43 based)
- Kernel 6.19.2-200.nobara.fc43.x86_64
- Mesa 26.0.0
- GPU: AMD Radeon RX 6600 (Navi 23, amdgpu)
- Monitor: Samsung TV (SAM 3574), 3840x2160@60Hz via HDMI
- DDC/CI: Not supported by monitor
This may be related to the brightness flickering fix in Plasma 6.4.5,
possibly a regression or incomplete fix for external monitors without DDC/CI.
===============================================================
NOBARA REPORT — File at:
https://github.com/Nobara-Project/nobara-core-packages/issues/new
===============================================================
Use the same title and description above. Add a note that this appears to
be an upstream KDE/KWin issue, filed here for visibility in case Nobara
carries any relevant patches.
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