[PATCH 1/1] irqchip: irq-gic: forward SGI to itself for cortex-a7 single core

[Mark Rutland]

On Mon, Aug 08, 2016 at 09:28:47PM +0800, Peter Chen wrote:
> On Mon, Aug 08, 2016 at 02:07:54PM +0100, Mark Rutland wrote:
> > I see that for arm64 we have:
> > 
> > static inline bool arch_irq_work_has_interrupt(void)
> > {
> > 	return !!__smp_cross_call;
> > }
> > 
> > Could we do similarly for ARM, and ony register gic_raise_softirq if
> > we have non-zero SGI targets?
> > 
> > If I've understood correctly, that would make things behave as they do
> > for UP on you system.

[...]

> > If self-IPI is necessary, then this would be up to the GIC code to
> > solve.
> > 
> > For that case, it would be nicer if we could detect whether this was
> > necessary based on the GIC registers alone. That way we handle the
> > various ways this can be integrated, aren't totally relient on the DT,
> > work in VMs, etc.
> 
> How we can detect IPI capabilities based on GIC register?

Check the mask associated with SGIs, as we do for gic_get_cpumask(). If
this is zero, we have a non-multiprocessor GIC (or one that's otherwise
broken), and can't do SGI in the usual way.

However, it only makes sense to do this if self-IPI is truly a
necessity. Given there are other interrupt controllers that can't do
self-IPI, avoiding self-IPI in general would be a better strategy,
avoiding churn in each and every driver...

Thanks,
Mark.