Arch Linux

alllexx88

Member

Registered: 2023-12-22

Posts: 52

nvidia dGPU+eGPU: Plasma on Wayland has black screen on dGPU

Hello,

I have a problem with Wayland Plasma sessions when using 2 different nvidia GPUs for outputing video on my laptop: dGPU RTX 4070 Max-Q for the Built-in screen and eGPU RTX 4070 Ti for an external monitor. I've been having problems with the eGPU likely due to a race condition with nvidia drivers trying to initialize the drm device before eGPU fully initializes. Thanks to great help from seth a workaround for this problem has been found: https://bbs.archlinux.org/viewtopic.php?id=300049.
The problem I'm facing now is that I have black screen with cursor from the eGPU output (dGPU output is fine) on SDDM on Wayland, and the opposite when I start a Plasma Wayland session from SDDM: black dGPU output with a cursor and an OK output from eGPU. If I start X11 session from SDDM, I get both dGPU and eGPU outputs working fine.

Some info from kscreen-doctor (note that I have the same external monitor connected twice, via eGPU and dGPU, hence the 3 outputs; eDP-1 is the black one, but if I enable DP-1 it's also black):

$ kscreen-doctor -i
Environment:
  * KSCREEN_BACKEND           : [not set]
  * KSCREEN_BACKEND_INPROCESS : [not set]
  * KSCREEN_LOGGING           : [not set]
Logging to                : [logging disabled]
Preferred KScreen backend : KSC_KWayland.so
Available KScreen backends:
  * KSC_Fake.so: /usr/lib/qt6/plugins/kf6/kscreen/KSC_Fake.so
  * KSC_KWayland.so: /usr/lib/qt6/plugins/kf6/kscreen/KSC_KWayland.so
  * KSC_QScreen.so: /usr/lib/qt6/plugins/kf6/kscreen/KSC_QScreen.so
  * KSC_XRandR.so: /usr/lib/qt6/plugins/kf6/kscreen/KSC_XRandR.so

$ kscreen-doctor -o
Output: 1 DP-4
        enabled
        connected
        priority 1
        DisplayPort
        Modes:  1:2560x1440@60!  2:2560x1440@165  3:2560x1440@144*  4:2560x1440@120  5:1920x1080@120  6:1920x1080@120  7:1920x1080@75  8:1920x1080@60  9:1920x1080@60  10:1920x1080@50  11:1680x1050@120  12:1680x1050@60  13:1280x1024@120  14:1280x1024@75  15:1280x1024@60  16:1440x900@120  17:1440x900@60  18:1280x720@60  19:1024x768@75  20:1024x768@60  21:800x600@75  22:800x600@60  23:720x576@50  24:720x480@60  25:640x480@75  26:640x480@60  27:640x480@60
        Geometry: 1829,0 2560x1440
        Scale: 1
        Rotation: 1
        Overscan: 0
        Vrr: incapable
        RgbRange: unknown
        HDR: incapable
        Wide Color Gamut: incapable
        ICC profile: none
        Color profile source: sRGB
        Brightness control: supported, set to 100%
Output: 2 DP-1
        disabled
        connected
        priority 0
        DisplayPort
        Modes:  28:2560x1440@60!  29:2560x1440@144*  30:2560x1440@120  31:1920x1080@120  32:1920x1080@75  33:1920x1080@60  34:1920x1080@50  35:1680x1050@120  36:1680x1050@60  37:1280x1024@120  38:1280x1024@75  39:1280x1024@60  40:1440x900@120  41:1440x900@60  42:1280x720@60  43:1280x720@50  44:1024x768@75  45:1024x768@60  46:800x600@75  47:800x600@60  48:720x576@50  49:720x480@60  50:640x480@75  51:640x480@60  52:640x480@60
        Geometry: 2048,0 2560x1440
        Scale: 1
        Rotation: 1
        Overscan: 0
        Vrr: incapable
        RgbRange: unknown
        HDR: incapable
        Wide Color Gamut: incapable
        ICC profile: none
        Color profile source: sRGB
        Brightness control: supported, set to 100%
Output: 3 eDP-1
        enabled
        connected
        priority 2
        Panel
        Modes:  53:2560x1600@60!  54:2560x1600@240*
        Geometry: 0,149 1829x1143
        Scale: 1.4
        Rotation: 1
        Overscan: 0
        Vrr: Automatic
        RgbRange: unknown
        HDR: incapable
        Wide Color Gamut: incapable
        ICC profile: none
        Color profile source: EDID
        Brightness control: supported, set to 100%

"qdbus org.kde.KWin /KWin supportInformation": http://0x0.st/XlOp.txt
Xorg log for an X11 session that works fine: http://0x0.st/XlOf.txt

Thanks