For the Debian installer boot issue, I tried
updating the system with the PNOR file here and now the LSI 9207-4i4e is working
For the OpenBSD installer issue, I've queried it on the OpenBSD ppc mailing list
In Debian, X is able to start on the VGA but it is not working through the RX 580 GPU. The screen flickers, sometimes it says there is no signal, nothing happens.
X logs show it is sees both the GPU and the monitor, it obtains the monitor ID string and supported resolutions.
I tried installing the jumper on the motherboard to disable the regular VGA, that has not helped.
I've tried various other things, for example
- disabled wayland in gdm config
- apt install firmware-linux-nonfree firmware-amd-graphics
- update the Debian kernel from buster-backports, 5.7.0-0.bpo.2-powerpc64le
Can anybody make any suggestions about how to get the GPU and display functional?