Comment # 25 on bug 1186896 from P

(In reply to Takashi Iwai from comment #20)

> In anyway, please report the issue to upstream if it happens with TW kernel.
> The upstream report should go to gitlab.freedesktop.org Issues.

I've opened AMD issue 1637:
https://gitlab.freedesktop.org/drm/amd/-/issues/1637

It was discovered this is actually an iommu problem. After adding `iommu=off`
to the boot params I was able to successfully boot the laptop. I now have
brightness + external screen. I'm now running on standard Leap 15.3 with the
default kernel (5.3.18) :-)

To avoid problems for future users, it may be useful to see if this iommu issue
is something which can be queried/determined at boot time of the installer.
Because the fix (`ommu=off`) is very simple, but I could never have figured
this out without expert help. Running into runtime issues is one thing, but not
even be able to start the installer is very unsettling. I was at the verge of
returning the laptop to the webshop for a refund.