linux-kernel - Re: [V9 PATCH 2/2] irqchip: gicv2m: Add supports for ARM GICv2m MSI(-X)

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Message-ID: <5457DE29.4020907@amd.com>
Date:	Mon, 3 Nov 2014 13:57:29 -0600
From:	Suravee Suthikulanit <suravee.suthikulpanit@....com>
To:	Marc Zyngier <marc.zyngier@....com>
CC:	Mark Rutland <Mark.Rutland@....com>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Catalin Marinas" <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	"Harish.Kasiviswanathan@....com" <Harish.Kasiviswanathan@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [V9 PATCH 2/2] irqchip: gicv2m: Add supports for ARM GICv2m MSI(-X)

On 11/3/2014 8:10 AM, Marc Zyngier wrote:
> On 03/11/14 09:50, Marc Zyngier wrote:
>
>>> @@ -843,10 +847,14 @@ static int gic_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
>>>          unsigned int type = IRQ_TYPE_NONE;
>>>          struct of_phandle_args *irq_data = arg;
>>>
>>> -       ret = gic_irq_domain_xlate(domain, irq_data->np, irq_data->args,
>>> -                                  irq_data->args_count, &hwirq, &type);
>>> -       if (ret)
>>> -               return ret;
>>> +       if (irq_data) {
>>> +               ret = gic_irq_domain_xlate(domain, irq_data->np, irq_data->args,
>>> +                                          irq_data->args_count, &hwirq, &type);
>>> +               if (ret)
>>> +                       return ret;
>>> +       } else {
>>> +               hwirq = virq;
>>> +       }
>>
>> I'm slightly puzzled here. What's the purpose of this? The whole goal of
>> the domain hierarchy is to avoid that kind of thing. Also, you should
>> never have to call xlate on an MSI, because it should never be described
>> in the device tree the first place.
>
> Thinking of it some more:
>
> The actual reason why this is required is because the MSI domain calls
> into this via irq_domain_alloc_irqs_parent(). But because MSIs are not
> described in DT, they do not have a of_phandle to pass down to the xlate
> helper. In this case, the v2m widget has the knowledge of what are the
> valid SPI numbers, and the core GIC code must blindly accept it.
>
> This definitely requires a fat comment, because this is far from obvious.
>
> Thanks,
>
> 	M.
>

I'll put in proper comments here.

Suravee

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