I see we lost this source line in the changes since 2.6.7.  But if I try
SATAPI expecting no data without this source line, then my ata_piix.ko
promptly dies with such complaints as:

kernel: irq 18: nobody cared!

With this source line, I find I can expect no data, though I still have
to add auto sense to overcome:

kernel: ata2: BUG: timeout without command