ahci, pata_marvell: play nicely together

ahci, pata_marvell: play nicely together

I've been chasing Jeff about this for months.  Jeff added the Marvell
device identifiers to the ahci driver without making the AHCI driver
handle the PATA port. This means a lot of users can't use current
kernels and in most distro cases can't even install.

This has been going on since March 2008 for the 6121 Marvell, and late 2007
for the 6145!!!

This was all pointed out at the time and repeatedly ignored. Bugs assigned
to Jeff about this are ignored also.

To quote Jeff in email

> "Just switch the order of 'ahci' and 'pata_marvell' in
> /etc/modprobe.conf, then use Fedora's tools regenerate the initrd.

> See?  It's not rocket science, and the current configuration can be
> easily made to work for Fedora users."

(Which isn't trivial, isn't end user, shouldn't be needed, and as it usually
breaks at install time is in fact impossible)

To quote Jeff in August 2007

> "   mv-ahci-pata
> Marvell 6121/6141 PATA support.  Needs fixing in the 'PATA controller
> command' area before it is usable, and can go upstream."

Only he add the ids anyway later and caused regressions, adding a further
id in March causing more regresions.

The actual fix for the moment is very simple. If the user has included
the pata_marvell driver let it drive the ports. If they've only selected
for SATA support give them the AHCI driver which will run the port a fraction
faster. Allow the user to control this decision via ahci.marvell_enable as
a module parameter so that distributions can ship 'it works' defaults and
smarter users (or config tools) can then flip it over it desired.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>