This is pretty much the same message I got from my built in controller for my ibook. The hard disks seem to go without DMA, but it's dog slow. I've been trying to debug this problem, but with little success. What does your /sbin/hdparm /dev/hdX say?
2.4.21ben2: (lots of lost interrupts) /dev/hde: multcount = 16 (on) I/O support = 0 (default 16-bit) unmaskirq = 0 (off) using_dma = 1 (on) keepsettings = 0 (off) nowerr = 0 (off) readonly = 0 (off) readahead = 8 (on) geometry = 119150/16/63, sectors = 120103200, start = 0 busstate = 1 (on) 2.4.20ben10: (works like a charm) /dev/hde: multcount = 0 (off) I/O support = 0 (default 16-bit) unmaskirq = 0 (off) using_dma = 1 (on) keepsettings = 0 (off) nowerr = 0 (off) readonly = 0 (off) readahead = 8 (on) geometry = 119150/16/63, sectors = 120103200, start = 0 busstate = 1 (on) looks like multcount is the key. -dorian