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

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Message-ID: <alpine.DEB.2.11.1410282116220.5308@nanos>
Date:	Tue, 28 Oct 2014 21:23:11 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Marc Zyngier <marc.zyngier@....com>
cc:	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Jonathan Corbet <corbet@....net>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Joerg Roedel <joro@...tes.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Matthias Brugger <matthias.bgg@...il.com>
Subject: Re: [Patch Part2 v3 01/24] irqdomain: Introduce new interfaces to
 support hierarchy irqdomains

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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