https://bugs.kde.org/show_bug.cgi?id=527184
Bug ID: 527184
Summary: [Wayland] Direct scanout causes rapid brightness/gamma
flicker over Chromium on Intel+NVIDIA hybrid GPU
Classification: Plasma
Product: kwin
Version First 6.8.0
Reported In:
Platform: Arch Linux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: wayland-generic
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
DESCRIPTION
Moving the mouse cursor over Chromium-based browser windows on a hybrid GPU
setup causes the screen brightness/gamma to rapidly flicker (dimming and
restoring in rapid bursts).
At the same time, kwin_wayland continuously logs:
"kwin_wayland: Failed to allocate a graphics buffer for a swapchain"
STEPS TO REPRODUCE
1. Run Plasma 6.8 on Wayland on a hybrid GPU setup (Intel iGPU + NVIDIA dGPU).
2. Set display scale to 125% with default `colorPowerTradeoff:
PreferEfficiency`.
3. Open Chromium / Google Chrome and move the cursor around inside the window.
OBSERVED RESULT
Screen brightness rapidly dips and flickers during cursor motion.
`journalctl --user -u plasma-kwin_wayland -f` spams:
kwin_wayland: Failed to allocate a graphics buffer for a swapchain
kwin_wayland: Failed to allocate a graphics buffer for a swapchain
EXPECTED RESULT
Smooth cursor movement and steady brightness without swapchain allocation
failures.
SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 6.8.0
KDE Frameworks Version: 6.31.0
Qt Version: 6.12.0
Graphics Platform: Wayland
ADDITIONAL INFORMATION
Hardware:
- GPUs: Intel Raptor Lake-S UHD Graphics (eDP-1) + NVIDIA GeForce RTX 5060
Mobile (nvidia-open 615.78.08, RTD3)
- Display: 1920x1080@144Hz, 125% scale, 8-bit SDR panel
Root Cause & Workarounds Tested:
1. Setting `colorPowerTradeoff: PreferAccuracy` via:
`kscreen-doctor output.eDP-1.colorPowerTradeoff.preferAccuracy`
immediately fixes the issue and eliminates the swapchain log spam.
2. Setting `KWIN_DRM_NO_DIRECT_SCANOUT=1` while keeping `PreferEfficiency` also
completely stops the flicker and the swapchain errors.
This indicates that under `PreferEfficiency`, KWin attempts MultiGpuSwapchain
direct scanout for Chromium's surface across the Intel/NVIDIA boundary, but
buffer allocation fails during cursor updates. Because the allocation failure
is not cached/inhibited, KWin rapidly alternates between direct scanout and
compositor pipelines on every frame/cursor event, causing gamma thrashing.
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