Not sure if this helps. I'm getting this reset with 2.6.21-rc4....
After the reset the controller seems to work again.
ata2.00: ATA-7: Maxtor 6V300F0, VA111630, max UDMA/133
ata2.00: 586114704 sectors, multi 16: LBA48 NCQ (depth 31/32)
ata2: EH in ADMA mode, notifier 0x0 notifier_error 0x0 gen_ctl 0x1501000 status 0x400 next cpb count 0x0 next cpb idx 0x0
ata2: CPB 1: ctl_flags 0x1f, resp_flags 0x2
ata2: timeout waiting for ADMA IDLE, stat=0x400
ata2: timeout waiting for ADMA LEGACY, stat=0x400
ata2.00: exception Emask 0x0 SAct 0x2 SErr 0x0 action 0x2 frozen
ata2.00: cmd 61/00:08:72:44:22/02:00:21:00:00/40 tag 1 cdb 0x0 data 262144 out
res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
ata2: soft resetting port
ata2: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
ata2.00: configured for UDMA/133
ata2: EH complete
SCSI device sda: 586114704 512-byte hdwr sectors (300091 MB)
sda: Write Protect is off
sda: Mode Sense: 00 3a 00 00
SCSI device sda: write cache: enabled, read cache: enabled, doesn't support DPO or FUA