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

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Date:	Wed, 29 Oct 2014 09:27:37 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Thomas Gleixner <tglx@...utronix.de>
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 28/10/14 20:23, Thomas Gleixner wrote:
> 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.

Quite.

>> 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.

Ah, that makes a lot more sense.

> But my question still stands:
> 
> Why would this check only apply if domain->ops->xlate is set?
> irq_create_mapping() does it unconditionally.

I don't think we should consider xlate at all. We already resolved hwirq
(either directly or through a xlate call), and the check should always
be performed (otherwise we're likely to fall into the same trap again).
Looks like a bug to me.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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