Index: sys/kern/subr_intr.c
===================================================================
--- sys/kern/subr_intr.c
+++ sys/kern/subr_intr.c
@@ -511,6 +511,17 @@
 	return (error);
 }
 
+/*
+ *  Lookup an interrupt source by irq.
+ */
+struct intr_irqsrc *
+intr_isrc_lookup(u_int irq)
+{
+	if (irq >= intr_nirq)
+		return (NULL);
+	return (irq_sources[irq]);
+}
+
 #ifdef SMP
 /*
  *  A support function for a PIC to decide if provided ISRC should be inited
Index: sys/sys/intr.h
===================================================================
--- sys/sys/intr.h
+++ sys/sys/intr.h
@@ -102,6 +102,7 @@
 int intr_isrc_deregister(struct intr_irqsrc *);
 int intr_isrc_register(struct intr_irqsrc *, device_t, u_int, const char *, ...)
     __printflike(4, 5);
+struct intr_irqsrc *intr_isrc_lookup(u_int irq);
 
 #ifdef SMP
 bool intr_isrc_init_on_cpu(struct intr_irqsrc *isrc, u_int cpu);