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SubjectRe: [PATCH -rt] powerpc update
Hello.

Ingo Molnar wrote:
> * Daniel Walker <dwalker@mvista.com> wrote:

>>Pay close attention to the fasteoi interrupt threading. I added usage
>>of mask/unmask instead of using level handling, which worked well on
>>PPC.

> this is wrong - it should be doing mask+ack.

It's what it was doing effectively. And what was wrong was calling ack()
which OpenPIC driver didn't (and was not obliged to) support.

> also note that you changed:

>>- goto out_unlock;

> to:

>>+ goto out;

> and you even tried to hide your tracks:
>
>
>> out:
>> desc->chip->eoi(irq);
>>-out_unlock:
>> spin_unlock(&desc->lock);

> :-)

> really, the ->eoi() op should only be called for true fasteoi cases.

Why is that? eoi() is effectively the same as ack() in this case. I must
note that what's the "standard" 8259 driver is doing in mask_ack() seems
misleading since it actually masks IRQ and sends EOI there.

> What we want here is to turn the fasteoi handler into a handler that
> does mask+ack and then unmask. Not 'mask+eoi ... unmask' as your patch
> does.

That's effectively the same for OpenPIC. Maybe that implemetation just
didn't look graceful but it was *correct*. And the current one is at least
incomplete.

I can see 3 ways to get out of this situation now:

1. Revert this change and use mask() + eoi() approach suggested by Daniel.

2. Add the ack() handler to OpenPIC driver -- and point it to mpic_eoi().

3. Do the same as x86 APIC driver does and use level/egde flows instead of
fasteoi for the case when IRQs are threaded -- that ensues doing (2) as well.

Note that all three aproaches lead to the effectively the same behavior
WRT OpenPIC (except for the edge-triggered IRQs in 3rd case). Opinions?

> Ingo

WBR, Sergei
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