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With the latest nvidia driver and linux 6.11 a phantom screen called unknown "39 is under gnome and from the testing forum (viewtopic.php?id=299450) it happens on other compositors also. I noticed simpledrm was initialized early and that creates 2 gfx cards under /dev/dri and this did not happen on 6.10.
I also had cachyos 6.11 installed and that had no issues. and i think i found the culprit and its in the config parameter: CONFIG_SYSFB_SIMPLEFB=y on cachyos this is not set and it defaults to "n"
I have tested with this not set or set to "n" and then the issue is gone.
The ArchWiki has been suggesting that this parameter is experimental and people should set nvidia_drm.modeset=1 via kernel parameters to activate the workaround instead.
This is because kernel 6.11 changed some `fbdev` related header file name, so the compiled `nvidia_drm` module does not have `fbdev` parameter. So `simpledrm` cannot be automatically disabled.
Apply this PR, and rebuild the kernel module, can fix this issue: https://github.com/NVIDIA/open-gpu-kern … s/pull/692
I tested that PR on the nvidia-open drivers and it seemed to fix the issue with the simpledrm phantom screen.
FTR I wanted to reinstate the skip simpledrm if nvidia-drm.modeset=1 is set patch in the next package release and keep it for the 6.11 cycle. I just didn't think it would take this long for 6.11.1 to appear.
Actually, in the Wiki it is "suggested"[1] to use the module parameters via modprobe.d. But this patch does not work, when applied to the module parameters so far I tested.
It explicitly needs to be set as kernel parameter.
Maybe there should be too some kind of info about this patch then.
FTR I wanted to reinstate the skip simpledrm if nvidia-drm.modeset=1 is set patch
@heftig, it appears this didn't happen? Not sure if directly related.. but now proprietary-Nvidia/Plasma/Wayland is badly broken causing affected users to roll back to 6.10. FWIW, I can repro in a pass-through VM. Basically SDDM comes up fine, but after logging in, black screen then nothing. X11 session seems to work.
Actually, adding nvidia_drm.fbdev=1 makes it work again (previously, this (experimental?) setting would cause weird glitches.. at least on this system).
And just FTR, I still get the phantom monitor under Gnome if nvidia_drm.fbdev=1 is absent. In other words, nvidia_drm.fbdev=1 seems to be required now.