maintainer-feedback requested: [Bug 245374] graphics/drm-fbsd12.0-kmod: kldload amdgpu on Vega64 halts the system

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Bug 245374: graphics/drm-fbsd12.0-kmod: kldload amdgpu on Vega64 halts the
system
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=245374



--- Description ---
Raised in https://github.com/FreeBSDDesktop/kms-drm/issues/232

Copy of the description below:

I know about the issue with drm-kfbsd12.0-kmod on 12.1. I found it when I tried
to fix the issue I am seeing.

I am using one system to build the kernel, world and packages and another, a
desktop, to install them.

The build system is running AMD Phenom and NVidia graphics card. I am using
poudriere to compile packages. The build system and the poudriere jail are
running FreeBSD-12.1-RELEASE-p3. On the build system I have also compiled a new
kernel and world from FBSD-12.1-RELEASE-p3 sources.

On the desktop where I am loading the module I have used FreeBSD-base packages
to install the kernel and world compiled on the build system. The desktop is
running on AMD Ryzen with Vega 64 graphics card.

Initially the desktop was running a stock version of FreeBSD-12.1-RELEASE-p3
with Generic kernel and the drm-kfbsd12.0-kmod build on the build system. The
behaviour is the same regardless if I am using GENERIC kernel/world or my own.

I am logging either as single or multi user into the command line. Then

kldload amdgpu

On the screen I see a bunch of drivers being loaded. There is a few loaded for
vega_10... then the screen goes blank. The system is halted. Any SSH session
are now defunct. Only power off/on is able to restart it.

I am happy to collect some debug information if you tell me how.