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

[Tejun Heo <tj@kernel.org>]

Hello,

On 01/11/2010 06:41 PM, Benjamin Herrenschmidt wrote:
> 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.

Eh.... I really hate this part of IDE.  :-(

> 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...

I think the only solution then is to disable the IRQ from the PIC.
We'll probably need to generalize there a bit as it seems there are
odd cases where we fall into IRQ storm but for now I think adding
special case code with sufficient comment should do it.

Thanks.

-- 
tejun