LG 27GP950-B should require DP 1.4a for DSC; Valve Index should only be DP 1.2.
Considering the card is DP 2.1 capable, both should easily be covered but I get zero display output or USB-C connectivity from this port. xrandr also shows no potential modes for DisplayPort-1, which is not promising.
My USB-C Samsung T5 SSD also doesn't ever mount when using the port, nor seems to indicate that it is receiving power. All other usb-c ports on the system work fine.
This behavior occurs on Win10 21H2 as well as Gentoo Linux kernel 6.1.2.
I initially had luck running my older Pixio PX7 (1440p 144hz) on the USB-C port with an adapter (https://smile.amazon.com/dp/B07F17ZHJY?psc=1), but the monitor was already in a dying state and became unusable shortly thereafter, hence why I replaced it with the LG 27GP950-B.
So far I've tried two adapters (https://smile.amazon.com/dp/B07F17ZHJY, and https://smile.amazon.com/dp/B08QV2FSKT) and one USB-C to DisplayPort 1.4 cable to no avail thus far for the new LG monitor or Valve Index (https://smile.amazon.com/dp/B01J6DT070).
Clearly, something is up with this USB-C port and it doesn't seem to be an OS-specific driver issue, and as a result one fourth of my gpu's outputs are useless, and considering the HDMI port can't handle the monitor or HMD in question, that is not a viable alternative.
EDIT: For reference, here's what I get in my syslog when attempting to plug in my USB-C SSD into the 7900 XTX:
Jan 4 16:34:14 gentoo kernel: xhci_hcd 0000:0f:00.2: Command completion event does not match command
Jan 4 16:34:14 gentoo kernel: xhci_hcd 0000:0f:00.2: ERROR mismatched command completion event
Jan 4 16:34:14 gentoo last message buffered 2 times
Jan 4 16:34:32 gentoo kernel: xhci_hcd 0000:0f:00.2: Error while assigning device slot ID: Command Aborted
Jan 4 16:34:32 gentoo kernel: xhci_hcd 0000:0f:00.2: Max number of devices this xHCI host supports is 64.
Jan 4 16:34:32 gentoo kernel: usb usb8-port1: couldn't allocate usb_device
Jan 4 16:34:45 gentoo kernel: xhci_hcd 0000:0f:00.2: Error while assigning device slot ID: Command Aborted
Jan 4 16:34:45 gentoo kernel: xhci_hcd 0000:0f:00.2: Max number of devices this xHCI host supports is 64.
Jan 4 16:34:45 gentoo kernel: usb usb8-port1: couldn't allocate usb_device
EDIT 2: It seems as of Linux kernel 6.1.3 my issue with USB-C and a DisplayPort 1.4 adapter has been fixed!
DisplayPort-1 connected 2160x3840+3840+0 left (normal left inverted right x axis y axis) 600mm x 340mm
3840x2160 144.00*+ 60.00 + 120.01 96.03 72.02 60.00 50.00 48.01 94.98
Not sure if Windows will be working now as well, as that is not my primary OS.
Have to report that the USB-C port has stopped working for any OS, kernel, mesa, or driver variation as of a few days ago. It worked for about a month and has randomly decided to stop working once again.
Opened an issue here (https://gitlab.freedesktop.org/drm/amd/-/issues/2415) but figured I'd ping this thread again.
It's back in a working state. Seems to potentially be an issue with my X570 Aorus Master interacting with the card at times as a full power-off with the PSU switch in the off-state overnight allowed it to work again the morning after.