Re: [Qemu-devel] [PATCH 0/2] irq: add get_gsi callback

[Paolo Bonzini <pbonzini@redhat.com>]

On 23/04/2015 11:40, Eric Auger wrote:
>> > Why can't you just use a GHashTable?
> You mean implementing this hash table in the interrupt controller?

No, in KVM.  Basically the kvm-vgic interrupt controller registers its 
qemu_irqs with kvm-all.c, passing the gsi number for KVM_IRQFD along 
the way.  Then VFIO device can pass the qemu_irq and ask for an irqfd 
for that qemu_irq, instead of having to know the gsi number.  kvm-all.c
acts as a mediator.

The notifier actually is not even necessary, because we already have
a very similar concept in QOM.  But qdev_init_gpio_out_named always
passes a dummy "notifier":

void qdev_init_gpio_out_named(DeviceState *dev, qemu_irq *pins,
                              const char *name, int n)
{
    int i;
    NamedGPIOList *gpio_list = qdev_get_named_gpio_list(dev, name);
    char *propname = g_strdup_printf("%s[*]", name ? name : "unnamed-gpio-out");

    assert(gpio_list->num_in == 0 || !name);
    gpio_list->num_out += n;

    for (i = 0; i < n; ++i) {
        memset(&pins[i], 0, sizeof(*pins));
        object_property_add_link(OBJECT(dev), propname, TYPE_IRQ,
                                 (Object **)&pins[i],
                                 object_property_allow_set_link,
                                 OBJ_PROP_LINK_UNREF_ON_RELEASE,
                                 &error_abort);
    } 
    g_free(propname);
}

So you need to add a method to DeviceClass, with the same prototype
as object_property_allow_set_link, and set the default value to
object_property_allow_set_link in device_class_init.  Then
qdev_init_gpio_out_named can do

    DeviceClass *dc = DEVICE_GET_CLASS(dev);
    ...
        object_property_add_link(OBJECT(dev), propname, TYPE_IRQ,
                                 (Object **)&pins[i],
                                 dc->gpio_set_hook,
                                 OBJ_PROP_LINK_UNREF_ON_RELEASE,
                                 &error_abort);

or something like that.

Alternatively, and probably better, add the argument to
qdev_init_gpio_out_named; there aren't many calls.  Then
you can add the method only to SysbusDeviceClass rather than
to all devices, and you can change sysbus_init_irq like this:

void sysbus_init_irq(SysBusDevice *dev, qemu_irq *p)
{
    SysBusDeviceClass *sdc = SYSBUS_DEVICE_GET_CLASS(dev);
    qdev_init_gpio_out_named(DEVICE(dev), p, SYSBUS_DEVICE_GPIO_IRQ, 1,
                             sdc->irq_set_hook);
}


Paolo

> The problem is my VFIO device currently has no link to the interrupt
> controller object. Besides it has a platform bus in between. Previously
> I devised a reset notifier called in the machine file to pass this link
> but Alex was not keen about this method. So the idea here is when the
> VFIO sysbus device qemuirq is getting connected, a notifier is called,
> VFIO device can retrieve the gsi of this qemu_irq and call KVM_IRQFD
> with that gsi.