KWin 6.5: USB-C DisplayPort not detected in Hybrid GPU mode (worked in 6.4.5)

Development
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1

# Issue Summary

After updating from KWin 6.4.5 to 6.5.0, my USB-C DisplayPort (physically wired to NVIDIA
dGPU) is no longer detected on my AMD+NVIDIA hybrid laptop. It worked perfectly in 6.4.5
without any special configuration.

Hardware

  • Laptop: ASUS ROG Zephyrus G15 GA503QR
  • GPU Setup: AMD iGPU (primary) + NVIDIA RTX 3070 Mobile (secondary)
  • Mode: Hybrid (supergfxctl) - both GPUs active
  • USB-C port is physically wired to NVIDIA card

What Works

  • Kernel detects display: `/sys/class/drm/card0-DP-2/status` = `connected`
  • Laptop screen (AMD eDP) works
  • HDMI port (AMD) works
  • `nvidia-drm.modeset=1` is set

What’s Broken

  • USB-C DisplayPort not detected in KDE Display Settings
  • `/sys/class/drm/card0-DP-2/enabled` stays `disabled`
  • KWin logs: `failed to open drm device at “/dev/dri/card0”`
  • `xrandr --listproviders` shows 0 providers (should show AMD + NVIDIA)

Timeline

  • **KWin 6.4.5-4:** Everything worked, no special config needed
  • **Oct 24:** Updated to KWin 6.5.0-1
  • **Oct 25:** USB-C display stopped working

Workaround Found

Setting `KWIN_DRM_DEVICES=/dev/dri/card1:/dev/dri/card0` restores functionality. I created a
mode-aware script in `~/.config/plasma-workspace/env/` that only applies this in Hybrid
mode.

Questions

  1. **Is this a regression or intentional behavior change?** Did KWin 6.5 change how it
    enumerates DRM devices in multi-GPU setups?
  2. **Should KWIN_DRM_DEVICES be required** for hybrid laptops where the dGPU has physical
    outputs?
  3. **Is anyone else experiencing this** on AMD+NVIDIA or Intel+NVIDIA hybrid laptops?

I have full technical details and logs if needed. Should I file a bug report, or is this
expected behavior?

**System:** Arch Linux, g-14 Kernel 6.17.4, KWin 6.5.0, NVIDIA 580.95.05, Plasma Wayland

2

That’s the source of the problem, but I don’t think KWin has any influence over it.

xrandr isn’t relevant.

Obviously not.

Works fine on my Intel+NVidia test setup.

4

agreed, because

I had to change manually.

5

I have a kind of similar problem. After the update, the DVI connections for the monitors on the docking station no longer work. However, the HDMI connection works.

The log says:
‘kwin_wayland_drm: failed to open drm device at \’\‘\n’

It’s a docking station for ThinkPad T490 with Intel UHD Graphics 620.