sysbus: add irq_routing_notifier

Add a new connect_irq_notifier notifier in the SysBusDeviceClass. This
notifier, if populated, is called after sysbus_connect_irq.

This mechanism is used to setup VFIO signaling once VFIO platform
devices get attached to their platform bus, on a machine init done
notifier.
Signed-off-by: NEric Auger <eric.auger@linaro.org>
Reviewed-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Tested-by: NVikram Sethi <vikrams@codeaurora.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>

hw/core/sysbus.c

@@ -109,7 +109,13 @@ qemu_irq sysbus_get_connected_irq(SysBusDevice *dev, int n)
 
 void sysbus_connect_irq(SysBusDevice *dev, int n, qemu_irq irq)
 {
+    SysBusDeviceClass *sbd = SYS_BUS_DEVICE_GET_CLASS(dev);
+
     qdev_connect_gpio_out_named(DEVICE(dev), SYSBUS_DEVICE_GPIO_IRQ, n, irq);
+
+    if (sbd->connect_irq_notifier) {
+        sbd->connect_irq_notifier(dev, irq);
+    }
 }
 
 /* Check whether an MMIO region exists */

include/hw/sysbus.h

@@ -58,6 +58,7 @@ typedef struct SysBusDeviceClass {
      * omitted then. (This is not considered a fatal error.)
      */
     char *(*explicit_ofw_unit_address)(const SysBusDevice *dev);
+    void (*connect_irq_notifier)(SysBusDevice *dev, qemu_irq irq);
 } SysBusDeviceClass;
 
 struct SysBusDevice {