[PATCH 6/6] ARM: gic: use handle_fasteoi_irq for SPIs

[tglx@linutronix.de (Thomas Gleixner)]

On Fri, 29 Apr 2011, Colin Cross wrote:
> > Cc: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
> > Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
> > Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> > Signed-off-by: Will Deacon <will.deacon@arm.com>
> 
> After further testing, I'm having a problem with this patch, although
> I think its more of a core issue than the fault of this patch.  One of
> my interrupts is getting stuck with the PENDING flag set, and
> preventing suspend.  The flow that triggers this is:
> 
> level triggered irq
>  handle_fasteoi_irq
>   handle_irq_event
>    isr
>     disable_irq_nosync
>     schedule_work (because it takes a sleeping i2c transaction to
> deassert the irq pin)

If you'd use a threaded irq handler the IRQ_ONESHOT mechanism would
handle that problem for you. It masks the irq line before calling the
handler and unmask happens after the threaded handler has run.

disable_irq_nosync from an interrupt handler plus scheduling work is
the historic "threaded" interrupt handler mechanism. It's kinda murky
nowadays due to the lazy irq disable mechanism.

>    irq_eoi
> same irq
>  handle_fasteoi_irq
>   mark irq pending
>   mask_irq
> work function
>  causes level triggered irq to go low
>  enable_irq
>   unmask_irq
>   check_irq_resend (returns immediately)
> 
> At this point, the irq is unmasked, but not being asserted, and marked
> as pending.  check_irq_resend doesn't clear the pending flag for level
> triggered interrupts, so the pending flag will stay set until the next
> time the interrupt occurs.

Yes, that should be cleared unconditionally in check_irq_resend.

> Should handle_fasteoi_irq mask the interrupt before eoi if it was
> disabled by the interrupt handler?  Otherwise, every level triggered
> interrupt that is not deasserted by the interrupt handler will
> interrupt the cpu twice.  There is still the case where a driver

No, we should stop doing the disable_irq_nosync from handlers and use
threaded interrupts instead.

> disables the irq, the interrupt goes high, then goes low again before
> enable_irq is called.

So what you're saying is:

irq ____                  _______
        |________________|       |_____________________

	    |                              |
	 ISR/mask/eoi                enable_irq/unmask

So after the unmask the asserted new interrupt is not delivered?
That's not a software problem :)

Thanks,

	tglx