MCP55 sata trouble

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

On amd64 including today's current, with:

viaide1: NVIDIA MCP55 Serial ATA Controller (rev. 0xa3)
wd0 at atabus1 drive 0: <ST3160812AS>
wd0: quirks 2<FORCE_LBA48>
wd0: drive supports 16-sector PIO transfers, LBA48 addressing
wd0: 149 GB, 310019 cyl, 16 head, 63 sec, 512 bytes/sect x 312500000 sectors
wd0: 32-bit data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd0(viaide1:0:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) (using DMA)
and same for wd1

I get lost interrupts. Now, at first I thought these were bad drives, but
it seems that there is a pattern between reboots: both work, one fails, the
other fails, repeat. By "fail" I mean lost interrupts, and timed out resets.

Any thoughts on this strange pattern?

Cheers,

Patrick