System lockup on kldload amdgpu

[Phil Norman]

Hi.

I have a Ryzen 2400G (built-in Vega graphics), and am trying to get it
working with x11 (on FreeBSD 12.0-STABLE r343112 GENERIC  amd64). Pete
Wright has been helping me out with instructions (over on freebsd-stable@),
and so far I've got as far as installing drm-kmod, and setting
'hw.sysconf.disable=1' in /boot/loader.conf.

However, on 'kldload amdgpu', the kldload process doesn't exit quickly, but
hangs (no new command-line prompt) for about 5s. Then the screen goes
blank, and my keyboard (caps lock led) and ethernet stop working. There are
more details, including /var/log/messages dumps, on the thread at
https://lists.freebsd.org/pipermail/freebsd-stable/2019-January/090491.html.

Can anyone please advise me on how I can get the amdgpu driver working? I'd
very much like to run this machine without a separate graphics card.

Thanks in advance,
Phil