https://bugs.kde.org/show_bug.cgi?id=521716
Bug ID: 521716
Summary: [Wayland] Black screen on iGPU display (cursor
visible) when forcing dGPU as primary via
KWIN_DRM_DEVICES on muxless hybrid setup
Classification: Plasma
Product: kwin
Version First 6.7.0
Reported In:
Platform: CachyOS
OS: Linux
Status: REPORTED
Severity: major
Priority: NOR
Component: compositing
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
DESCRIPTION
When explicitly setting the discrete GPU as the primary renderer in a hybrid
graphics setup on Plasma 6.7 (Wayland), the screen connected to the integrated
GPU fails to render the desktop, showing a black screen with only a working
hardware cursor.
STEPS TO REPRODUCE
1. Use a laptop with a muxless AMD Hybrid Graphics setup (AMD Ryzen 7 5800H
with Radeon Graphics + AMD Radeon RX 6700M, no MUX switch available).
2. Force KWin to use the dGPU as the primary renderer by exporting:
KWIN_DRM_DEVICES="/dev/dri/by-path/pci-0000:03:00.0-card:/dev/dri/by-path/pci-0000:06:00.0-card"
3. Log into a Plasma Wayland session with the internal laptop screen active.
OBSERVED RESULT
The desktop environment fails to render on the internal laptop screen (iGPU).
The screen is completely black, but the hardware cursor is fully visible and
can be moved around normally. External monitors connected directly to the dGPU
render perfectly with zero latency.
EXPECTED RESULT
The desktop should be rendered properly on the iGPU display via KWin's
multi-GPU copying, just like it did in previous Plasma versions.
SOFTWARE/OS VERSIONS
Operating System: CachyOS Linux
KDE Plasma Version: 6.7.0
KDE Frameworks Version: 6.27.0
Qt Version: 6.11.1
Kernel Version: 7.0.12-1-cachyos (64-bit)
Graphics Platform: Wayland
ADDITIONAL INFORMATION
Adding the environment variable `KWIN_DRM_USE_MODIFIERS=0` fixes the issue
completely. With this variable, the laptop screen renders perfectly again while
keeping the dGPU as primary.
This suggests the regression is directly related to how the dGPU is
compressing/sending the frames to the older Renoir iGPU using DRM modifiers
under the new Vulkan multi-GPU swapchain introduced recently.
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