Re: 2.6.33-rc2 pata_macio fails to detect PMac G3 CD-drive

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2010-01-11 at 16:01 +0900, Tejun Heo wrote:
> It would be best if the controller has an IRQ pending bit and IRQ can
> be cleared as spurious on those bogus interrupts.  The reason why SFF
> IDE interface is so prone to IRQ storm is because there's no way the
> driver can tell whether the controller is raising interrupt or not.
> Does the controller have a way to clear IRQ other than reading the
> status reg?

Nope. Those old Apple controllers have neither a pending bit nor a
clear, I think the disk interrupt is wired pretty much directly to
the PIC.

I can't tell for sure about Mikael's precise case because I can't
reproduce it, but in the past, I've seen the CD drive act up similarily
when touching NIEN on a wallstreet powerbook (same controller, though
for some reason it doesn't act up for me right now) and reading the
status reg wasn't clearing the IRQ neither.

I suspect those guys have the IRQ in some kind of floating state after
the HW reset and don't get it "right" until they get the first taskfile
to kick them into some kind of shape...

Cheers,
Ben.