Re: [Xen-devel] [RFC 7/8] xen/arm: Allow DOM0 to set the irq type when ACPI is inuse

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 22 Jun 2016, Julien Grall wrote:
> > > @@ -356,6 +375,8 @@ void vgic_enable_irqs(struct vcpu *v, uint32_t r, int
> > > n)
> > >           {
> > >               irq_set_affinity(p->desc, cpumask_of(v_target->processor));
> > >               spin_lock_irqsave(&p->desc->lock, flags);
> > > +            if ( irq_type_set_by_domain(d) )
> > > +                gic_set_irq_type(p->desc, __vgic_get_virq_type(v, irq));
> > >               p->desc->handler->enable(p->desc);
> > >               spin_unlock_irqrestore(&p->desc->lock, flags);
> > >           }
> > 
> > This is OK. But I am wondering if it wouldn't make sense to call
> > gic_set_irq_type when the guest actually writes to the virtual icfg?
> 
> Hmmm it looks like that I forgot to explain in the commit message why I chose
> to call gic_set_irq_type here.
> 
> Changing the value of Int_config is UNPREDICTABLE when the corresponding
> interrupt is not disabled (see 4.3.13 in ARM IHI 0048B.b).
> 
> So calling gic_set_irq_type when the guest actualy writes to the virtual cfg
> would require to disable the IRQ before hand.
> 
> Given that the behavior is UNPREDICTABLE, I chose to set the type before
> enabling the IRQ because the resulting code is simpler.

Ah, I see. Makes sense.

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