[PATCH] ARM: gic: use handle_fasteoi_irq for SPIs

Will Deacon will.deacon at arm.com
Fri Feb 18 06:29:31 EST 2011

> >> Right, so to get back to the original discussion about how to handle
> >> chained handlers if the high-level flow type of the IRQ chip is altered
> >> it seems that there are two options:
> >>
> >> 1.) Update all of the chained handlers to use the new flow-control
> >> 2.) Retain backwards compatibility if a chained handler decides to
> >>     use the old method of flow control (specifically, leave an ack
> >>     implementation in the GIC code after moving to fasteoi).
> >>
> >> Obviously, I'd rather go with option (2) and let platforms migrate
> >> over time if they choose to. Now, given that the ack function is really
> >> not something you want to do in a virtualised environment (because it
> >> pokes the distributor), is it worth sticking a
> >> WARN_ON_ONCE(cpu_has_virtualisation()); in the ack code?
> >
> > #2 is less painful and just works. The fasteoi stuff does not use ack
> > IIRC so it wont hurt.
> On an MSM we use handle_percpu_irq for PPIs, if we have ack and eoi we
> will end up EOI ing the interrupt twice so #2 wont work. Also all the
> cascaded handlers would have assumed that the ack function masks the
> interrupt, it is best we fix all of them to use eoi at the end (just
> like handle_fasteoi_irq). Please tell me how you guys locate such
> cascaded handlers?

I don't think the cascaded handlers would have assumed that because ack
just sends EOI - it doesn't do any masking. We do have a problem with
the percpu_irq flow though (the GIC reference manual says that EOIing a
non-active interrupt is UNPREDICTABLE).

Another easy hack is to set IRQ_PER_CPU in the irq_desc->status for PPI
interrupts and then check this in the ack routine. It's pretty ugly, but
it doesn't affect the common case and it at least postpones the platform

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