Hello,
I've built a new machine with VT6421 add-on card that has two SATA and one 
PATA port:

sata_via 0000:00:0a.0: version 2.2
sata_via 0000:00:0a.0: routed to hard irq line 12
scsi0 : sata_via
scsi1 : sata_via
scsi2 : sata_via
ata1: SATA max UDMA/133 cmd 0x00016300 ctl 0x0001630a bmdma 0x00016700 irq 12
ata2: SATA max UDMA/133 cmd 0x00016400 ctl 0x0001640a bmdma 0x00016708 irq 12
ata3: PATA max UDMA/133 cmd 0x00016500 ctl 0x0001650a bmdma 0x00016710 irq 12


The SATA port works fine with Samsung 500GB HDD:

ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
ata1.00: ATA-8: SAMSUNG HD501LJ, CR100-10, max UDMA7
ata1.00: 976773168 sectors, multi 16: LBA48 NCQ (depth 0/32)
ata1.00: configured for UDMA/133

But there are write problems with the PATA port with Seagate 250GB HDD:

ata3.00: ATA-7: ST3250823A, 3.03, max UDMA/100
ata3.00: 488397168 sectors, multi 16: LBA48
ata3.00: configured for UDMA/100

Reading works but writing any longer data stream causes errors like this:

ata3.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x2 frozen
ata3.00: cmd 35/00:40:97:c6:87/00:01:16:00:00/e0 tag 0 cdb 0x0 data 163840 out
         res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
ata3: soft resetting port
ata3.00: configured for UDMA/100
ata3: EH complete
ata3.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x2 frozen
ata3.00: cmd 35/00:00:df:d1:87/00:04:16:00:00/e0 tag 0 cdb 0x0 data 524288 out
         res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
ata3: soft resetting port
ata3.00: configured for UDMA/100
ata3: EH complete
sd 2:0:0:0: [sdb] 488397168 512-byte hardware sectors (250059 MB)
sd 2:0:0:0: [sdb] Write Protect is off
sd 2:0:0:0: [sdb] Mode Sense: 00 3a 00 00
sd 2:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support 
DPO or FUA
sd 2:0:0:0: [sdb] 488397168 512-byte hardware sectors (250059 MB)
sd 2:0:0:0: [sdb] Write Protect is off
sd 2:0:0:0: [sdb] Mode Sense: 00 3a 00 00
sd 2:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support 
DPO or FUA

The transfer mode decreases from UDMA/100 to UDMA/66 and then UDMA/33 but it 
doesn't help at all. The drive itself is fine, the problems also appear with 
4.3GB Seagate drive. But there are no problems with WD 700MB drive (PIO 
mode). I think that it's some kind of UDMA problem.

Kernel is 2.6.22.3, older 2.6.21.5 was also affected. Complete dmesg output is 
attached.

-- 
Ondrej Zary