From mboxrd@z Thu Jan  1 00:00:00 1970
From: Suravee Suthikulanit <suravee.suthikulpanit@amd.com>
Subject: Re: [V9 PATCH 2/2] irqchip: gicv2m: Add supports for ARM GICv2m MSI(-X)
Date: Mon, 3 Nov 2014 13:57:29 -0600
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To: Marc Zyngier <marc.zyngier@arm.com>
Cc: Mark Rutland <Mark.Rutland@arm.com>, "jason@lakedaemon.net" <jason@lakedaemon.net>, "tglx@linutronix.de" <tglx@linutronix.de>, Catalin Marinas <Catalin.Marinas@arm.com>, Will Deacon <Will.Deacon@arm.com>, Liviu Dudau <Liviu.Dudau@arm.com>, "Harish.Kasiviswanathan@amd.com" <Harish.Kasiviswanathan@amd.com>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>, "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
List-Id: devicetree@vger.kernel.org

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