It can't be that that much of an issue, because OpenBSD runs on these machines (according to [4] and my tests on serveral PRIMEPOWER 250s). And for the Linux kernel you can actually see some Linux kernel messages before the machine experiences a red state exception... [4]: http://www.openbsd.org/sparc64.html
I avoid the openbsd people and try to just look to freebsd :
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=233579
Which actually is making good progress in the IBM Power9 world on the
TALOS as well as on ye old ppc64 PowerMac units and sparc is in progress
also. With ZFS everywhere.
Anyways, that is well off topic.
dc