INSTALL kernel page fault with SATA port-multiplexer backplanes

[brook%biology.nmsu.edu@localhost (Brook Milligan)]

I am trying to build a system that uses some Syba SY-PEX40008 SATA
controllers, each backed by port-multiplexers that contain SiL3726
chipsets.  Unfortunately, the INSTALL kernel page faults when the
first controller is detected:

     siisata0 port 0: device present, speed: 3.0Gb/s

     Followed by:

     Fatal page fault in supervisor mode.
     trap type 6 code 0 rip ffffffff802faf80 cs 8 rflags 10202 cr2 50 cpl 6 rsp 
ffff80005580aa38
     kernel: page fault trap, code=0
     stopped in pid 0.32 (system) at 0xffffffff802faf80: call *0x50(%r14)

If the backplanes are removed, the system will boot and install, but I
am not yet certain whether the installed system will run with the
backplanes reinstalled.

Are these (or any?) SATA port-multiplexer backplanes supported in
NetBSD?

Thanks for your help.

Cheers,
Brook