Re: [PATCH v8 08/12] hw/arm/virt: Allow user-creatable SMMUv3 dev instantiation

[Nicolin Chen <nicolinc@nvidia.com>]

On Fri, Jul 18, 2025 at 08:01:22AM +0000, Shameerali Kolothum Thodi wrote:
> > > +    int irq = platform_bus_get_irqn(pbus, sbdev, 0);
> > > +    hwaddr base = platform_bus_get_mmio_addr(pbus, sbdev, 0);
> > > +    MachineState *ms = MACHINE(vms);
> > > +
> > > +    if (!(vms->bootinfo.firmware_loaded && virt_is_acpi_enabled(vms))
> > &&
> > > +        strcmp("pcie.0", bus->qbus.name)) {
> > > +        warn_report("SMMUv3 device only supported with pcie.0 for DT");
> > > +        return;
> > > +    }
> > > +    base += vms->memmap[VIRT_PLATFORM_BUS].base;
> > > +    irq += vms->irqmap[VIRT_PLATFORM_BUS];
> > 
> > The code is fine.
> > 
> > Just a related question here:
> > 
> > Do you know where we define the number of IRQs and the range of
> > MMIO for the SysBusDevice?
> > 
> > SMMU has four IRQs. And I see multiple vSMMU instances do have
> > correct intervals to their IRQ numbers, but I cannot find where
> > the magic is done.
> 
> Look for,
> #define PLATFORM_BUS_NUM_IRQS 64
> 
> So in theory we could have around 16 vSMMU per VM. It depends on
> other platform devices specified as well. Do you see a need for more
> on a per VM basis? I know there are host systems with large number of
> SMMUv3s, but how many a VM will get assigned realistically?

Hmm, I was asking how platform bus knows that SMMU only has four
IRQs. But I think number of 16 might not be enough in some cases.

So, my question was: where do we set the number of 4 to the sbdev?
As platform_bus_get_irqn() returned very correctly with 0, 4, 8,
and so on..

Thanks
Nicolin