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

[Suravee Suthikulpanit]

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@xxxxxxx 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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