Cannot enable DMA on SATA drive (SCSI-libsata, VIA SATA)

[Petter Sundlöf]

Using 2.6.8.1. DMA works fine on /dev/hda (PATA, CD burner).

When I try to enable it for my SATA drive (which is performing horribly 
bad -- 80-90% CPU load on an AMD64 3200+ during copy of large files) I 
get this error:

# hdparm -d 1 /dev/sda

/dev/sda:
 setting using_dma to 1 (on)
 HDIO_SET_DMA failed: Invalid argument

Tried different commands:

# hdparm -X66 -d1 /dev/sda

/dev/sda:
 setting using_dma to 1 (on)
 HDIO_SET_DMA failed: Invalid argument
 setting xfermode to 66 (UltraDMA mode2)
 HDIO_DRIVE_CMD(setxfermode) failed: Invalid argument

hdparm -d /dev/sda gives absolutely no information.

The chipset is VIA82Cxx (ASUS K8VSE Deluxe motherboard). Disk is Maxtor 
6Y200M0.

Seen in /proc/scsi/scsi like this:

Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: ATA      Model: Maxtor 6Y200M0   Rev: YAR5
  Type:   Direct-Access                    ANSI SCSI revision: 05

I also have the Promise controller, which I can use use a regular SATA 
controller (not RAID as is default). Should I attach it to it instead 
(I'd rather not if it can be avoided).

dmesg info:

libata version 1.02 loaded.
sata_via version 0.20
ACPI: PCI interrupt 0000:00:0f.0[B] -> GSI 20 (level, low) -> IRQ 20
sata_via(0000:00:0f.0): routed to hard irq line 10
ata1: SATA max UDMA/133 cmd 0xE400 ctl 0xE002 bmdma 0xD000 irq 20
ata2: SATA max UDMA/133 cmd 0xD800 ctl 0xD402 bmdma 0xD008 irq 20
ata1: dev 0 cfg 49:2f00 82:7c6b 83:7f09 84:4003 85:7c69 86:3e01 87:4003 
88:407f
ata1: dev 0 ATA, max UDMA/133, 398297088 sectors: lba48
ata1: dev 0 configured for UDMA/133
scsi0 : sata_via
ata2: no device found (phy stat 00000000)
scsi1 : sata_via
  Vendor: ATA       Model: Maxtor 6Y200M0    Rev: YAR5
  Type:   Direct-Access                      ANSI SCSI revision: 05
SCSI device sda: 398297088 512-byte hdwr sectors (203928 MB)
SCSI device sda: drive cache: write back
 /dev/scsi/host0/bus0/target0/lun0: p1 p2 < p5 p6 p7 p8 p9 p10 p11 p12 
p13 >
Attached scsi disk sda at scsi0, channel 0, id 0, lun 0
Attached scsi generic sg0 at scsi0, channel 0, id 0, lun 0,  type 0
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