kern/103602: drive gets wedged on READ CD CAPACITY if no disc is in

[Josh Carroll]

> *And* you mentioned, very early in this PR, that disabling DMA
> altogether made the problem disappear. So, let's try something: enable
> DMA only for READ and WRITE commands (where it's most useful).
>
> Apparently it's not a completely unhead-of situation that some drives
> have problems with DMA for commands other than READ and WRITE, see:
> http://www.mail-archive.com/linux-ide@vger.kernel.org/msg05425.html
>

Hi Thomas,

Unfortunately, the other patches along with this produced a panic
about a MTX not owned, and removing the CAMDEBUG options resulted in a
different panic about ATAPICAM not locked. I'll look more closely
tonight to see if I can get the kernel to load without a panic.

Thanks,
Josh