Hi,
I have a laptop with an ICH6M SATA Controller and a Hitachi hard drive.
While it worked well using the ahci module and Linux 2.6.25, 
it get randomly 'stuck' for several seconds to several minutes with 2.6.26-rc8.
Successive errors progressively reduce the ATA link speed.

Passing the libata.noacpi parameter is an effective workaround.

Please note that it's not the first time i have this kind of issue, see:
http://marc.info/?l=linux-ide&m=117305595312399&w=2
This was found to be a bad interaction between my _GTF taskfile, which enable the
"Enable Device-Initiated Interface Power State Transitions" feature, and NCQ.
The driver was later NCQ blacklisted to correct the problem.


Device detection:

[    0.567684] ahci 0000:00:1f.2: version 3.0
[    1.568027] ahci 0000:00:1f.2: AHCI 0001.0000 32 slots 4 ports 1.5 Gbps 0x5 impl IDE mode
[    1.568091] ahci 0000:00:1f.2: flags: 64bit ncq pm led slum part 
[    1.568695] ata1: SATA max UDMA/133 abar m1024@0xb8000c00 port 0xb8000d00 irq 19
[    1.873016] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[    1.874045] ata1.00: ACPI cmd ef/10:03:00:00:00:a0 succeeded
[    1.875000] ata1.00: ATA-7: HTS541010G9SA00, MBZOC60D, max UDMA/100
[    1.875000] ata1.00: 195371568 sectors, multi 0: LBA48 NCQ (not used)
[    1.875000] ata1.00: ACPI cmd ef/10:03:00:00:00:a0 succeeded
[    1.875000] ata1.00: configured for UDMA/100

Typical error:

[  499.178040] ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
[  499.178105] ata1.00: cmd ca/00:3e:76:45:81/00:00:00:00:00/e1 tag 0 dma 31744 out
[  499.178106]          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
[  499.178168] ata1.00: status: { DRDY }
[  499.178220] ata1: hard resetting link
[  499.942034] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[  499.943540] ata1.00: ACPI cmd ef/10:03:00:00:00:a0 succeeded
[  499.946056] ata1.00: ACPI cmd ef/10:03:00:00:00:a0 succeeded
[  499.947174] ata1.00: configured for UDMA/100
[  499.947174] ata1: EH complete

Full dmesg is attached.

-- 
Mathieu Bérard