Re: [Bulk] Re: [patch 2.6.18] genirq: remove oops with fasteoiirq_chip descriptors

From: Thomas Gleixner
Date: Wed Sep 27 2006 - 21:23:48 EST


On Wed, 2006-09-27 at 17:39 -0700, David Brownell wrote:
> - It wouldn't use chip->mask_ack() when that exists and those
> other two routines don't, even though mask_ack_irq() is a
> conveniently defined inline.

So why not replace it by mask_ack_irq() ?

> - Umm, how could it ever be correct to leave the IRQ active
> without a dispatcher? ISTR the rationale for that delayed
> disable was not purely to be a PITA for all driver writers,
> but was to address some issue with edge triggering. In that
> path, triggering was no longer to be allowed ...

Your patch would result in default_disable() when no shutdown function
is provided. default_disable() does the delayed disable thing, while you
remove the handler. The next event on that line will cause a spurious

> - Plus ack()ing the IRQ there just seemed pretty dubious. It's
> not like there would be anything preventing that signal line
> from being lowered (or raised, etc) immediately after the ack(),
> which in some hardware would latch the IRQ until later unmask().
> Leaving the question: what's the point of it?? The overall
> system has to behave sanely with or without the ack(); just
> clearing a latch doesn't mean it couldn't get set later.

Fair enough.

> > > So what's the correct fix then ... use enable() and disable()?
> > > Oopsing isn't OK...
> >
> > True, but we can not unconditionally change the semantics.
> Some current semantics are "it oopses". That's a good definition
> of semantics that _must_ be changed. We're not Microsoft. ;)

Agreed, it just depends on how they get fixed.

> > Does it break existing or new code ?
> Could any code relying on those previous semantics have been
> correct in the first place, though? Seemed to me it couldn't
> have been.
> Plus, unregistering IRQ dispatchers is a strange notion. I've
> never seen it done in practice ... normally, they get set up once
> during chip/board setup then never changed. Bugs in code paths
> like that have been known to last for decades unfixed.

Agreed. Nothing is using this currently.

> > Sorry, I did not think about the defaults in the first place. The
> > conditionals in manage,c are probably superflous leftovers from one of
> > the evolvement.
> And that's how I was taking that particular mask() then ack() too,
> especially given it never used mask_ack() when it should have, and
> since that logic oopsed in various cases with fasteoi handlers.

The remaining question is whether mask_ack_irq() or shutdown() is the
correct approach. Your patch would make it mandatory to implement
shutdown at least for such removable stuff.

I'm not sure about that right now as I'm too tired.


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