IBM LC921

Hi,

I'm trying to get FreeBSD to run on an IBM LC921.  The wiki mentions the
LC922, which I think is the same Supermicro P9DSU-C but in 2U, so
presumably someone had this working at some point.  Anyway, two snags so
far:

1. The latest PNOR from IBM (V2.18-20210329) won't start any version of
FreeBSD with ISOs currently available.  It just reboots with a
checkstop.  I installed Linux and built kexec-lite and this does seem to
work, but it would be nice if FreeBSD booted directly.

2. When switching over from the intermediate Linux (currently 6.1.0), it
says:

[23465.263516] xhci_hcd 0005:01:00.0: Host halt failed, -110

Then FreeBSD panics with:

xhci0: <XHCI (generic) USB 3.0 controller> mem 0x80000000-0x8000ffff,0x80010000-0x80011fff irq 1030136 at device 0.0 numa-domain 0 on pci12
xhci0: 64 bytes context size, 64-bit DMA
xhci0: Controller halt timeout.
xhci0: XHCI halt/start/probe failed err=18
xhci0: Controller halt timeout.

fatal kernel trap:

   exception       = 0x300 (data storage interrupt)
   (...)
   curthread       = 0xc0080000b258c840
          pid = 12, comm = irq39774168: xhci0

The PNOR kernel doesn't say anything about USB when kexec-ing, so maybe
this is a bug in the newer/stock Linux I'm hopping through.

This is as far as I've gotten.  Any hints would be appreciated.  I'm
happy to test patches if anyone's interested.

Thanks!