[Arch][Linux 4.17.8-1][Dual GTX 970] Cannot run identical cards in SLI/BaseMosaic mode, happens only when nvidia_drm module is loaded

Hello!

I have encountered a very strange problem where it is impossible for me to use dual video cards in SLI or Base Mosaic mode.

When I try, my monitors all go black, and then enter power save mode.
I can still SSH into the machine, which means the computer is not going through a hard lockup.

I have tried the following resolution steps :

  • Load Older Drivers
  • Load an LTS kernel
  • Swapped the SLI Bridge Cable
  • Uninstall and reinstall current drivers
  • Install Legacy Drivers
  • Turned IOMMU options on and off
  • Rebooted many times
  • Turn off compositing
  • Tested with a regular X server session and a Graphical Boot Manager
  • Create a fresh Xorg.conf file using nvidia-xconfig, nvidia-xconfig --sli=on, nvidia-xconfig --sli = mosaic, nvidia-xconfig --base-mosaic --sli=off
  • Load Modules One At A Time
  • I found much to my surprise that if I load all BUT the nvidia_drm module, I can start an X session, KDE, and a Graphical Boot Manager just fine.

    It’s only when I try to start X with nvidia_drm do I get the noted behavior above.
    I get the following output when I check my DMESG output: https://pastebin.com/nKvCG90z

    EDIT ATTACHED NVIDIA BUG REPORT

    UPDATE:

    Like a fool, I forgot to RTM, and didn’t catch chapter 33, as per https://bbs.archlinux.org/viewtopic.php?pid=1798739#p1798739.

    To any others with this issue, make sure to disable KMS before using SLI.

    Have a great day, all!
    nvidia-bug-report.log.gz (487 KB)