irq: introduce qemu_irq_proxy()

In some cases we have a circular dependency involving irqs - the irq
controller depends on a bus, which in turn depends on the irq controller.
Add qemu_irq_proxy() which acts as a passthrough, except that the target
irq may be set later on.
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NAvi Kivity <avi@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/irq.c

@@ -90,3 +90,17 @@ qemu_irq qemu_irq_split(qemu_irq irq1, qemu_irq irq2)
     s[1] = irq2;
     return qemu_allocate_irqs(qemu_splitirq, s, 1)[0];
 }
+
+static void proxy_irq_handler(void *opaque, int n, int level)
+{
+    qemu_irq **target = opaque;
+
+    if (*target) {
+        qemu_set_irq((*target)[n], level);
+    }
+}
+
+qemu_irq *qemu_irq_proxy(qemu_irq **target, int n)
+{
+    return qemu_allocate_irqs(proxy_irq_handler, target, n);
+}

hw/irq.h

@@ -33,4 +33,9 @@ qemu_irq qemu_irq_invert(qemu_irq irq);
 /* Returns a new IRQ which feeds into both the passed IRQs */
 qemu_irq qemu_irq_split(qemu_irq irq1, qemu_irq irq2);
 
+/* Returns a new IRQ set which connects 1:1 to another IRQ set, which
+ * may be set later.
+ */
+qemu_irq *qemu_irq_proxy(qemu_irq **target, int n);
+
 #endif