Having trouble enabling DMA on your nForce 3 mobo?

After getting jerky DVD playback I noticed that DMA was not being enabled for my IDE DVD drive. The canonical hdparm -d1 /dev/cdrom resulted in a rude "Permission denied".

It seems that to enable DMA, the amd74xx, ide-cd and ide-generic need to be loaded in this order, or you’ll loose DMA and end up with something like this in your system log:

NFORCE3-250: port 0x01f0 already claimed by ide0