quoted

+	if (ata_pio_need_iordy(adev) || use_mwdma)
  		control |= 2;	/* IE enable */

    Why IORDY is enabled for MWDMA has always been beyond me... I understand 
that the stupid Intel docs are to be blamed here.

I fail to see whats stupid about the docs ?

The same timing register set is used for MWDMA and PIO cycles in MWDMA
tuned modes (eg ATAPI). Thus the controller needs to be in an MWDMA mode
whose timings are compatible with the PIO timing and we want IORDY in use
for the PIO transfer parts.

Alan