ahci-timeout regression in beta3

[Harry Schmalzbauer]

 Hello,

I have a remote machine with a probably defective ODD, but until r294989
(from Jan 28th) I could boot with just these warnings:
(cd1:ahcich1:0:0:0): READ(10). CDB: 28 00 00 38 85 e0 00 00 01 00
(cd1:ahcich1:0:0:0): CAM status: SCSI Status Error
(cd1:ahcich1:0:0:0): SCSI status: Check Condition
(cd1:ahcich1:0:0:0): SCSI sense: MEDIUM ERROR asc:11,0 (Unrecovered read
error)
(cd1:ahcich1:0:0:0): Error 5, Unretryable error
(cd1:ahcich1:0:0:0): cddone: got error 0x5 back
…

beta3 doesn't boot anymore, it's hanging with ahci-timeouts:
ahcich2: Timeout on slot 11 port 0
ahcich2: is 00000008 cs 00000000 ss 00000000 rs 00000800 tfd 40 derr
00000000 cmd 0004cb17
(ada1:ahcich2:0:0:0): READ_FPDMA_QUEUED. ACB: 60 01 ae a3 50 40 5d 01 00
00 00 00
...
(aprobe0:ahcich2:0:0:0) ATA_IDENTIFY. ACB eec 00 00 00 00 40 00 00 00 00
00 00
(aprobe0:ahcich2:0:0:0) CAM status: Command timeout
(aprobe0:ahcich2:0:0:0) Error 5, Retry was blocked
ada1 detached
...
The numbers (first ACB) and also the channel varies from time to time.

I couldn't track down the revision yet, checked r295124 and r295131 so far.
Just noticed that probing differs between working (294989) and and
non-working revisoin (r296074): The latter attaches cd past ada, the
former (working) probes cd first.

Will see to find out more until next weekend.
Any hints welcome.

Thanks,

-Harry