AHCI/ADA regression?

There appears to be a regression in AHCI/ADA behavior since r300207.

Starting a test kernel at r300293 results in extremely long timeouts
probing ahcich2 for non-existent multiplier ports.

Here some kernel output:
ahci0: <AMD SB7x0/SB8x0/SB9x0 AHCI SATA controller>
port 0xff00-0xff07,0xfe00-0xfe03,0xfd00-0xfd07,0xfc00-0xfc03,
0xfb00-0xfb0f mem 0xfe02f000-0xfe02f3ff irq 22 at device 17.0 on pci0

ahci0: AHCI v1.10 with 6 3Gbps ports, Port Multiplier supported

ahcich2: <AHCI channel> at channel 2 on ahci0

ada1 at ahcich2 bus 0 scbus2 target 0 lun 0

/dev/ada1p1 on /home (ufs, local, journaled soft-updates)

An older kernel at r299170 does not exhibit this peculiar behavior and
mounts /home with no delays.

-- 
Gary Jennejohn