linux-kernel - Re: [V10 PATCH 2/2] irqchip: gicv2m: Add supports for ARM GICv2m MSI(-X)

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Message-ID: <5458E0BE.2090803@amd.com>
Date:	Tue, 4 Nov 2014 08:20:46 -0600
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Marc Zyngier <marc.zyngier@....com>,
	Mark Rutland <mark.rutland@....com>, <jason@...edaemon.net>,
	<Catalin.Marinas@....com>, <Will.Deacon@....com>,
	<liviu.dudau@....com>, <Harish.Kasiviswanathan@....com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [V10 PATCH 2/2] irqchip: gicv2m: Add supports for ARM GICv2m
 MSI(-X)



On 11/4/14 04:06, Thomas Gleixner wrote:
> On Mon, 3 Nov 2014, Suravee Suthikulanit wrote:
>> On 11/3/2014 4:51 PM, Thomas Gleixner wrote:
>>> On Mon, 3 Nov 2014, suravee.suthikulpanit@....com wrote:
>>>> +	irq_domain_set_hwirq_and_chip(v2m->domain, virq, hwirq,
>>>> +				&v2m_chip, v2m);
>>>> +
>>>> +	irq_set_msi_desc(hwirq, desc);
>>>> +	irq_set_irq_type(hwirq, IRQ_TYPE_EDGE_RISING);
>>>
>>> Sure both calls work perfectly fine as long as virq == hwirq, right?
>>
>> I was running into an issue when calling the irq_domain_alloc_irq_parent(), it
>> requires of_phandle_args pointer to be passed in. However, this does not work
>> for GICv2m since it does not have interrupt information in the device tree.
>> So, I decided at first to use direct (virq == hwirq) mapping, which simplifies
>> the code a bit, but might not be ideal solution, as you pointed out.
>
> It's not only far from ideal. It's not a solution at all. Simply
> because there is no guarantee for virq == hwirq.
>
>> An alternative would be to create a temporary struct of_phandle_args, and
>> populate it with the interrupt information for the requested MSI. Then pass it
>> to:
>>    --> irq_domain_alloc_irq_parent
>>     |--> gic_irq_domain_alloc
>>       |--> gic_irq_domain_xlate
>>       |--> gic_irq_domain_map
>>
>> However, this would still not be ideal if we want to support ACPI. Another
>
> Neither device tree nor ACPI has anything to do with MSI interrupts at
> runtime.
>
> All they do is to tell that there is a MSI controller and where the
> registers are and in the worst case fixups for a borked MSI_TYPER
> register.
>
> So either the TYPER reg or DT/ACPI gives you a fixed hwirq range which
> is reserved for MSI. And that's all you need, right?
>
Right, I get that part. Figuring out the fixed hwirq range for MSI is 
not the point I am trying to make here.

> [...]
> All you need is to pick one hwirq out of the existing fixed range and
> associate it to a newly allocated virq. That's the only information
> the underlying gic domain has to know about, because it needs to
> translate from the hwirq to the virq in the low level entry handler
> gic_handle_irq().

And that's what I am trying to do here except that GIC is expecting that 
information to be passed to it via irq_domain_alloc_irqs(..., args) 
where args is struct of_phandle_args (e.g. in the kernel/irqdomain.c: 
irq_create_of_mapping). This works fine when specifying interrupt from 
DT, but that is not always the case.

Currently, I can just create a fake of_phandle_args just to pass the 
hwirq information to GIC.

     --> gicv2m_setup_msi_irq()
      |    struct of_phandle_args phan;
      |    phan.np = NULL;
      |    phan.args_count = 3;
      |    phan.args[0] = 0;
      |    phan.args[1] = hwirq - 32;
      |    phan.args[2] = IRQ_TYPE_EDGE_RISING;
      |--> irq_domain_alloc_irqs(d, 1, NUMA_NO_NODE, &phan);
       |--> gicv2m_domain_alloc(d, virq, nr_irqs, arg)
	|--> irq_domain_alloc_irqs_parent(d, virq, nr_irqs, arg);

I am trying to figure out what would be a common data structure for this 
purpose that would work for both Dt and non-DT case (e.g. GICv2m MSI). 
Unless you think this is ok.

Thanks,
Suravee
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