[arch-general] Dual graphics not working in Lenovo P53

[LuKaRo]

Hi all,

My new Lenovo P53 has an Intel UHD Graphics 630 and a NVIDIA Quadro 
T1000 built in. The HDMI port seems to be wired to the NVIDIA graphics. 
However, dual graphics is not working.

When using the nvidia driver and the nvidia-prime package, I can run 
games on the NVIDIA card using prime-run. But xrandr only shows "eDP1" 
(internal screen) and "VIRTUAL0", no external ports are recognized.

When using xf86-video-nouveau, xrandr shows several DP and eDP-ports and 
the HDMI port. However, the ports are always shown as "disconnected", 
even when a HDMI cable is connected (works on another Arch Linux 
machine). Furthermore, DRI_PRIME=1 glxinfo | grep "OpenGL renderer" 
always shows the UHD 630.

Any ideas how to debug or fix this issue?

Thanks a lot,
LuKaRo