Comment 21 for bug 36185

I believe some controllers are known to have buggy DMA, but those are mostly
already handled by the IDE driver.

For CDROM's maybe we can have a minimum criteria to start with for allowing a
drive to have DMA enabled by default. Something like:

1) Is it DVD capable? Most of the complaints about DMA by default revolve around
playback of DVD video. If the drive is not capable of reading DVD's, then DMA is
not as important (by default).

2) Since there's no universal way of detecting "newer" DVD drives, possibly we
can just check for something like supporting a minimum drive speed (say 24x
CDROM speed), maybe enable DMA on all DVD recorders.

3) If we can get the above criteria to give us like 99% reliability that it is
only enabled by default on hardware that works, then we can start a black/white
list of vendor/model/firmware for the few cases left.

The alternative is to disable DMA always during installation and let the kernel
do its normal thing when booting into the system (in fact, I think we should
always disable DMA during installation for reliable CD installs). This wouldn't
work for live-cd of course.