OpenBSD 7.5 as the IO domain on T5220: the Intel driver failed to initialize

Hi,

I have a Sun Oracle Netra T5220.  I'm running Solaris 11.3 as the
control domain.  I want my OpenBSD to be an IO domain, i.e., a domain
that has direct access to IO: in my case, the four RJ45 network
interfaces on the back of the server (plus an NVMe card).  In T5220,
the four interfaces connect to two Intel 82571EB chips, which in turn
connect to a single PCIe bus.

So in Solaris I first enable IO virtualization for the PCIe bus:

root@solaris:~# ldm set-io iov=on pci

And then assign these two chips to my IO domain:

root@solaris:~# ldm add-io MB/NET0 router
root@solaris:~# ldm add-io MB/NET2 router

Everything looks good:

root@solaris:~# ldm list-io

NAME                        TYPE   BUS      DOMAIN    STATUS
----                        ----   ---      ------    ------
pci                         BUS    pci      primary   IOV
niu                         NIU    niu      primary
MB/RISER0/PCIE0             PCIE   pci      router    OCC
MB/RISER1/PCIE1             PCIE   pci      primary   EMP
MB/RISER2/PCIE2             PCIE   pci      primary   EMP
MB/PCI_MEZZ/PCIE5           PCIE   pci      primary   EMP
MB/NET0                     PCIE   pci      router    OCC
MB/NET2                     PCIE   pci      router    OCC
MB/SASHBA                   PCIE   pci      primary   OCC

However, OpenBSD is unable to initialize the interfaces:

em0 at pci4 dev 0 function 0 "Intel 82571EB" rev 0x06: couldn't map 
interrupt
em1 at pci4 dev 0 function 1 "Intel 82571EB" rev 0x06: couldn't map 
interrupt
em2 at pci5 dev 0 function 0 "Intel 82571EB" rev 0x06: couldn't map 
interrupt
em3 at pci5 dev 0 function 1 "Intel 82571EB" rev 0x06: couldn't map 
interrupt

I think the OpenBSD em driver is to blame (and not the
virtualization), because I also assigned an NVMe card to the very same
OpenBSD system and it works great.

Before I ran OpenBSD 7.5 as the control domain without the IO
virtualization enabled, and the interfaces worked fine.  I found a
similar issue described here, where they ran OpenBSD as a guest
system:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=205445

There the conclusion was:

 > The OpenBSD em/iwm drivers may either not use MSI, or require legacy
 > interrupts to be valid before using MSI.

I don't know what to do with this.  I would appreciate it someone
could give me some clue.


Thanks & best,
Irek