Re: [Patch Part2 v3 01/24] irqdomain: Introduce new interfaces to support hierarchy irqdomains

[Thomas Gleixner]

On Tue, 28 Oct 2014, Marc Zyngier wrote:
> On 28/10/14 19:37, Thomas Gleixner wrote:
> > So while we are at it:
> > 
> >> +	if (irq_domain_is_hierarchy(domain)) {
> >> +		if (domain->ops->xlate) {
> >> +			/*
> >> +			 * If we've already configured this interrupt,
> >> +			 * don't do it again, or hell will break loose.
> >> +			 */
> >> +			virq = irq_find_mapping(domain, hwirq);
> >> +			if (virq)
> >> +				return virq;
> > 
> > I can understand that it is an issue if the mapping exists already,
> > but I have to ask WHY is it correct behaviour to call into that code
> > for an existing mapping.
> 
> As I have originally looked at this, I'll answer the question:
> 
> The generic DT code parses the whole tree, and generates platform
> devices as it goes. As part of the platform device creation, it
> populates the IRQ resources, which translates into calling into
> irq_create_of_mapping(). You could argue that this behaviour is crazy,
> and I wouldn't disagree.

Mooo.

> See http://www.spinics.net/lists/devicetree/msg53164.html for more gory
> details.
> 
> > And why would this check only apply if domain->ops->xlate is set?
> > irq_create_mapping() does it unconditionally.
> 
> My original code used the xlate callback to parse the opaque irq_data,
> computing hwirq, and I suspect this is a leftover of it. The above code
> seems to pull hwirq out of thin air, which is probably not the intended
> behaviour. Joe?

No. Here is the full patch from Joe:

  http://lists.infradead.org/pipermail/linux-arm-kernel/2014-October/296543.html

hwirq gets either set from hwirq = irq_data->args[0] or from the xlate
call.

But my question still stands:

Why would this check only apply if domain->ops->xlate is set?
irq_create_mapping() does it unconditionally.

Thanks,

	tglx
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