Index: mp_machdep.c
===================================================================
RCS file: /usr/cvs/src/sys/i386/i386/mp_machdep.c,v
retrieving revision 1.115.2.23
diff -u -r1.115.2.23 mp_machdep.c
--- mp_machdep.c	13 May 2005 00:10:55 -0000	1.115.2.23
+++ mp_machdep.c	15 Jun 2005 15:51:55 -0000
@@ -1663,8 +1663,8 @@
 #define SRCBUSID(I)	(io_apic_ints[(I)].src_bus_id)
 #define SRCBUSDEVICE(I)	((io_apic_ints[(I)].src_bus_irq >> 2) & 0x1f)
 #define SRCBUSLINE(I)	(io_apic_ints[(I)].src_bus_irq & 0x03)
-int
-pci_apic_irq(int pciBus, int pciDevice, int pciInt)
+static int
+pci_apic_irq_raw(int pciBus, int pciDevice, int pciInt)
 {
 	int     intr;
 
@@ -1686,6 +1686,72 @@
 	return -1;					/* NOT found */
 }
 
+static int
+pci_apic_bus_present(int bus)
+{
+	int intr;
+
+	for (intr = 0; intr < nintrs; ++intr)
+		if ((INTTYPE(intr) == 0) && (SRCBUSID(intr) == bus))
+			return (1);
+	return (0);
+}
+
+int
+pci_apic_irq(int bus, int device, int pin)
+{
+	device_t dev, bus_dev, pcib;
+	int irq;
+
+	pcib = NULL;
+loop:
+	/* See if there is an exact match first. */
+	printf("APIC_IO: trying to route %d:%d INT%c\n", bus, device,
+	    pin + 'A' - 1);
+	irq = pci_apic_irq_raw(bus, device, pin);
+	if (irq != -1)
+		return (irq);
+
+	/* If this bus has other entries but not this one, punt. */
+	if (pci_apic_bus_present(bus))
+		return (-1);
+
+	/* Safety net, don't try to walk past bus 0. */
+	if (bus == 0)
+		return (-1);
+
+	/*
+	 * Try to find ourself.  Every device has a function of 0 and we are
+	 * really just trying to find our parent, so assume a function of 0
+	 * to find either ourself or one of our siblings.  If we are recursing
+	 * up the chain, we need to find the previous bridge's parent bus
+	 * instead.
+	 */
+	if (pcib == NULL) {
+		dev = pci_find_bsf(bus, device, 0);
+		if (dev == NULL)
+			return (-1);
+	} else
+		dev = pcib;
+	bus_dev = device_get_parent(dev);
+	if (bus_dev == NULL)
+		return (-1);
+	pcib = device_get_parent(bus_dev);
+	if (pcib == NULL)
+		return (-1);
+
+	/*
+	 * Do the swizzle thing.
+	 *
+	 * XXX: no error checking for the bus number here
+	 * (valid, does it exist, etc.).
+	 */
+	bus = pcib_get_bus(pcib);
+	pin = (pci_get_slot(pcib) + (pin - 1)) % 4 + 1;
+	device = pci_get_slot(pcib);
+	goto loop;
+}
+
 int
 next_apic_irq(int irq) 
 {