Re: [PATCH -rt] powerpc update

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Ingo Molnar wrote:
* Daniel Walker <[email protected]> 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;


+		goto out;

and you even tried to hide your tracks:



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?


WBR, Sergei
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