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

From: Thomas Gleixner <tglx@linutronix.de>
To: Marc Zyngier <marc.zyngier@arm.com>
Cc: Yingjoe Chen <yingjoe.chen@mediatek.com>,
	Jiang Liu <jiang.liu@linux.intel.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Yinghai Lu <yinghai@kernel.org>, Borislav Petkov <bp@alien8.de>,
	"grant.likely@linaro.org" <grant.likely@linaro.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tony Luck <tony.luck@intel.com>, Joerg Roedel <joro@8bytes.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>
Subject: Re: [Patch Part2 v3 01/24] irqdomain: Introduce new interfaces to support hierarchy irqdomains
Date: Tue, 28 Oct 2014 21:23:11 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.11.1410282116220.5308@nanos> (raw)
In-Reply-To: <544FF900.4020601@arm.com>

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