[arch-general] AMDGPU does not show consider external DisplayPort monitors on PRIME laptop

[Giovanni Santini]

Hi all,

I thought it would be easier to ask here first; if I should open a bug
report on the Arch or any other tracker, I can definetely do so.

I have an ASUS laptop with a Ryzen 4800H and a Geforce RTX 2060 Mobile.
All is good, except the support of external monitors via DisplayPort.
While previously I used HDMI via a single monitor, I finally took from
my workplace my working monitors and connected them in daisy chain and
connected the laptop to them via USB-C to USB-C.

The whole setup works on Windows, but on Linux I cannot make it work
when using the AMDGPU driver.
I tried disabling it and using the NVIDIA one via `optimus-manager` and
the latter can easily detect and handle all the monitors.
The weird fact is that DisplayPort partially works with AMDGPU, as I am
able to use my mouse and headset connected to the monitor but I cannot
detect any monitor to display images.

I honestly have no clue why this problem sussists.
I need and would like some tips for investigating the issue and
reporting where necessary.

Thanks in advance.

Bests,

Giovanni