xserver does not see secondary GPU devices when they are present when Xorg starts
1.20 is fine, but with master I'm seeing the following:
- Take a machine using i915 display hardware + an udl device, both using the modesetting driver
- Start Xorg
- I do see: [ 1327.722] (II) xfree86: Adding drm device (/dev/dri/card0) [ 1327.722] (II) systemd-logind: got fd for /dev/dri/card0 ... messages for both /dev/dri/card0 and /dev/dri/card1
- But xrandr --listproviders only shows the i915 GPU.
- Unplug + replug the udl device, now it does show up (leaving it unplugged and plugging it in after starting Xorg also works)
IIRC secondary GPU additions is suppressed during the initial cold plug, so that the primary GPU is the first device, but there should be code which adds the skipped secondary GPUs once the cold plug phase is done, this seems to be broken in master.