> Can you try to boot a kernel without siop to see what PCI vendor/device
> ID this adapter has ?

Done. 

	Symbios Logic 53c875/876 (SCSI mass storage, revision 0x14) at pci1 dev 1 
function 0 not configured
	Symbios Logic 53c875/876 (SCSI mass storage, revision 0x14) at pci1 dev 1 
function 1 not configured

Working backwards through pcidevs gives us a product id of 0x000f and a vendor 
id of 0x1000. This all agrees with the output from .properties. See below. I'm 
afraid that I can't get a core dump. ddb(4) says that the sync command should 
generate one, but it doesn't.

ok .properties 
assigned-addresses       81020810 00000000 00000400 00000000 00000100 
                         82020814 00000000 00002000 00000000 00000100 
                         82020818 00000000 00004000 00000000 00001000 
device_type              scsi-2
clock-frequency          02625a00 
reg                      00020800 00000000 00000000 00000000 00000000 
                         01020810 00000000 00000000 00000000 00000100 
                         02020814 00000000 00000000 00000000 00000100 
                         02020818 00000000 00000000 00000000 00001000 
model                    Symbios,53C875
compatible               glm
name                     scsi
devsel-speed             00000001 
class-code               00010000 
interrupts               00000001 
max-latency              00000040 
min-grant                00000011 
subsystem-vendor-id      00001000 
subsystem-id             00001000 
revision-id              00000014 
device-id                0000000f 
vendor-id                00001000