With today's sources (including the very latest interrupt stuff) I get
on my 5900:

	scsibus0 at xasc0: 8 targets, 8 luns per target
	scsibus0: waiting 2 seconds for devices to settle...
	probe(xasc0:0:0): max sync rate 5.00MB/s
	sd0 at scsibus0 target 0 lun 0: <DEC, RZ26     (C) DEC, T386> SCSI2 0/direct fixed
	sd0: 1001 MB, 2570 cyl, 14 head, 57 sec, 512 bytes/sect x 2050860 sectors
	 ...
	boot device: sd0
	root on sd0a dumps on sd0b
	no file system for sd0 (dev 0x1300)
	cannot mount root, error = 79
	root device (default sd0a): 

My May 15 kernel works fine...

Simon.