pci powerstate related: aac(4) broken on Perc 3/Di on -CURRENT

[Warner Losh]

> This type of thing is why I've always been very nervous about the
> automatic power management control that was committed to the tree.  The
> above example is completely in spec, but we are taking the liberty of
> assuming that all unattached devices should be powered down (modulo the
> exception that was made for video devices).  I don't know of a generic
> way to fix this; you'll have to either add an exception to the PM code
> for these specific SCSI devices, or write a do-nothing driver to attach
> to it so it doesn't get spammed by the PM code.  Either way it's just an
> exception for this paarticular case, and who knows how many other cases
> with similar needs will be broken when 6.0 is released?

I understand your nervousness.  However, the automatic pm code is a
huge win for most people, a very huge win for some poeple, so I'm
going to be pushing very hard to have it be on by default.  I didn't
turn it on by default for 5.x, and the understanding at the time was
that it would be turned on for 6.0 by default unless there was some
compelling reason to not do so.  So far, the exception list is tiny,
and easy to manage.  We'll see how things go as we get experience with
these things.  I'm committed to making it work, and have shown a
willingness to do what is necessary to make it work.  Until that
changes, I'd appreciate the benefit of the doubt.

I'll be committing the appropriate driver to the tree for the system
device class.  I'm hoping to do it in a way that makes it trivial to
override for other things (eg, you just write a probe function, and
nothing else).

Warner