I noticed that the promise driver doesn't work when the device is in dma mode.

wd2: transfer error, downgrading to DMA mode 2
wd2(pciide2:1:0): using PIO mode 4, DMA mode 2 (using DMA data transfers)
wd2e: DMA error reading fsbn 9558208 of 9558208-9558223 (wd2 bn 29718208; cn 29482 tn 5 sn 37), retrying
pciide2:1:0: lost interrupt
         type: ata
         c_bcount: 8192
         c_skip: 0
pciide2:1:0: Bus-Master DMA error: missing interrupt, status=0x1
wd2: transfer error, downgrading to PIO mode 4
wd2(pciide2:1:0): using PIO mode 4


-- 
Matt Thomas               Internet:   matt@3am-software.com
3am Software Foundry      WWW URL:    http://www.3am-software.com/bio/matt/
Cupertino, CA             Disclaimer: I avow all knowledge of this message