Re: [PATCH v2 6/9] irqchip / gic: Add stacked irqdomain support for ACPI based GICv2 init

[Hanjun Guo]

Hi Marc,

On 06/29/2015 04:39 PM, Marc Zyngier wrote:
> On 27/06/15 04:52, Hanjun Guo wrote:
> > On 06/24/2015 01:38 AM, Lorenzo Pieralisi wrote:
> > > On Tue, Jun 23, 2015 at 04:11:38PM +0100, Hanjun Guo wrote:
[...]
> > > > > >     	for (i = 0; i < nr_irqs; i++)
> > > > > >     		gic_irq_domain_map(domain, virq + i, hwirq + i);
> > > > > > @@ -945,11 +952,11 @@ void __init gic_init_bases(unsigned int gic_nr, int irq_start,
> > > > > >     		gic_irqs = 1020;
> > > > > >     	gic->gic_irqs = gic_irqs;
> > > > > >
> > > > > > -	if (node) {		/* DT case */
> > > > > > +	if (node || !acpi_disabled) {		/* DT or ACPI case */
> > > > > >     		gic->domain = irq_domain_add_linear(node, gic_irqs,
> > > > > >     						    &gic_irq_domain_hierarchy_ops,
> > > > > >     						    gic);
> > >
> > > I think this is a bit more worrying, I mean passing a NULL node pointer to
> > > the irqdomain layer which basically means you are booting out of ACPI
> >
> > I'm little confused here, would you mind explaining more for your
> > worrying? To me, node pointer is optional and it's ok for ACPI
> > case.
> >
> > > (for you, if that's true for the irq_domain_add_linear implementation
> > > that's another story), the node pointer should be optional but you
> > > need feedback from IRQ layer maintainers here.
> >
> > Sure.
>
> Frankly, I'd really like to see ACPI using the "node" parameter for
> something useful. This would save having to cache pointers all over the
> place, will make find_irq_host() work as expected... etc.
>
> See the comment at the top of linux/irqdomain.h :
>
> "... This code could thus be used on other architectures by replacing
> those two by some sort of arch-specific void * "token" used to identify
> interrupt controllers."

To init GIC in ACPI, we can only use the table entry pointer as
the token, but the ACPI static tables are early mem/io remapped
memory at boot stage, and it will be not available after boot,
also we need muti types of MADT enties to init GIC (GICC and GICD
for GICv2, GICC or GICR and GICD for GICv3), not as DT, just
one single node to include all the information needed to init
the GIC.

We use ACPI handle for devices as node for DT when the namespace
is available, but that's pretty late in the boot stage which GIC,
SMP and timers were already initialized, so ACPI handle can not
use as the token too.

I see multi places just pass NULL as the pointer directly for
irq_domain_add_linear() which works fine, and for ACPI, we tested
this patch and also it works.

> Maybe it is time to bite the bullet.

Hope comment above explains :)

Thanks
Hanjun
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