diff --git a/src/hardware/pci/bios-v2/bios-v2.c b/src/hardware/pci/bios-v2/bios-v2.c
index e6ade61..14c1237 100644
--- a/src/hardware/pci/bios-v2/bios-v2.c
+++ b/src/hardware/pci/bios-v2/bios-v2.c
@@ -79,11 +79,49 @@ struct	{
 	IRQRoutingOptionsBuffer	buf;
 	uint8_t					databuf [2048];
 	} route_buf;
+	
 
 static	uint64_t	free_mem_start, free_mem_end;
 static	uint32_t	lastbus, version, hardware;
 int					verbose = 0;
 
+typedef struct _pci_reverse_bus_list {
+    struct _pci_reverse_bus_list* next;
+    uint8_t sec_bus;
+    uint8_t bus;
+    uint8_t devfunc;
+} pci_reverse_bus_list;
+
+static pci_reverse_bus_list    ** find_reverse_bus(uint8_t sec_bus) {
+    static pci_reverse_bus_list    *reverse_bus_list = NULL;
+
+	slogf (_SLOGC_PCI, _SLOG_DEBUG1, "Looking up reverse bus for %d", sec_bus);
+    
+    pci_reverse_bus_list** reverse_bus_list_entry = &reverse_bus_list;
+    while ((*reverse_bus_list_entry != NULL) && ((*reverse_bus_list_entry)->sec_bus != sec_bus)) {
+        reverse_bus_list_entry = &((*reverse_bus_list_entry)->next);
+    };
+    if (*reverse_bus_list_entry) {    
+        slogf (_SLOGC_PCI, _SLOG_DEBUG1, "Found bus %d dev %d at %08X", 
+            (*reverse_bus_list_entry)->bus,
+            PCI_DEVNO((*reverse_bus_list_entry)->devfunc),
+            (intptr_t)reverse_bus_list_entry
+        );
+    } else {
+        slogf (_SLOGC_PCI, _SLOG_DEBUG1, "Not found! Last value is %08X (from %08X)", 
+            (intptr_t)reverse_bus_list_entry,
+            (intptr_t)&reverse_bus_list
+        );
+    };
+        
+    return reverse_bus_list_entry;
+};
+
+static uint32_t pci_irq_swizzle(uint8_t devfunc, uint32_t intpin ) {
+    return ((((intpin -1) + PCI_DEVNO(devfunc)) % 4) +1);
+};
+
+
 sigjmp_buf	env;
 
 /**************************************************************************/
@@ -303,7 +341,25 @@ int				i, irq, found;
 			}
 		}
 	if (!found) {
-		slogf (_SLOGC_PCI, _SLOG_ERROR, "Bus %d device %x - No routing found", bus, PCI_DEVNO(devfn));
+		slogf (_SLOGC_PCI, _SLOG_ERROR, "Bus %d device %x pin %d - No routing found", bus, PCI_DEVNO(devfn),intpin);
+		/* This might be because we're behind a PCI-to-PCI bridge.  If so, we can */
+		/* try looking up at the previous bridge, and so on, until we get a match. */
+		if (bus > 0) {
+		    /* Since we have no way to easily interact with the bus list maintained by the server, we do this the hard way */		    
+		    while (bus) {
+		        pci_reverse_bus_list** parent = find_reverse_bus(bus);
+		        if (*parent) {
+		            intpin = pci_irq_swizzle(devfn,intpin);
+                    bus = (*parent)->bus;
+                    devfn = (*parent)->devfunc;
+		            int result = scan_irq_routing(handle,bus,devfn,intpin,intel);
+		            if (result != -1) return result;		                
+		        } else {
+		            return -1;
+		        };
+		    };
+		}
+		
 		return (-1);
 		}
 	if (r->irq [intpin - 1].link) {
@@ -642,7 +698,10 @@ uint8_t	*databuffer;
 int		bios_cnfg_bridge (void *handle, uint32_t bus, uint32_t devfunc, pci_bus_t *pbus)
 
 {
-bios_dev_t		*pdev = handle;
+    bios_dev_t		*pdev = handle;
+    int				i;
+    uint32_t		dword = 0;
+    int pri_bus, sec_bus;
 
 	DEBUGFUNC();
 	if (pbus->pciex_addr != NULL) {
@@ -650,6 +709,40 @@ bios_dev_t		*pdev = handle;
 		pdev->pciex_size = pbus->pciex_size;
 		}
 
+    /* Add an entry to the reverse bus list, for IRQ mapping */
+	/* this config read will return 4 bytes. Byte 0 is the primary bus, should be the same as 'bus'. Byte 1 is the secondary bus */
+	if ((i = bios_read_cnfg (handle, bus, devfunc, offsetof (struct _pci_bridge_config_regs, Primary_Bus_Number),
+							 4, &dword)) != PCI_SUCCESS) {
+		return (i);
+	}    
+	pri_bus = dword & 0xFF;
+	sec_bus = (dword >> 8) & 0xff;
+    if ((pri_bus == bus) && (sec_bus != 0)) {
+        pci_reverse_bus_list** reverse_bus_list_entry = find_reverse_bus(sec_bus);
+        
+        if (!*reverse_bus_list_entry) { 
+            *reverse_bus_list_entry = malloc(sizeof(pci_reverse_bus_list)); 
+            slogf (_SLOGC_PCI, _SLOG_DEBUG1, "Adding new entry for %d at %X, neext address is %X",
+                pbus->sub_bus,
+                (intptr_t)reverse_bus_list_entry,
+                (intptr_t)&((*reverse_bus_list_entry)->next)
+            );
+            if (*reverse_bus_list_entry) { (*reverse_bus_list_entry)->next = NULL; };
+        };
+        if (*reverse_bus_list_entry) { 
+            slogf (_SLOGC_PCI, _SLOG_DEBUG1, "Updating at %X: B: %d D: %d SB: %d",
+                (intptr_t)reverse_bus_list_entry,
+                bus,
+                devfunc,
+                pbus->sub_bus
+            );
+            
+            (*reverse_bus_list_entry)->bus = bus;
+            (*reverse_bus_list_entry)->devfunc = devfunc;
+            (*reverse_bus_list_entry)->sec_bus = sec_bus;
+        };
+    };
+
 	return (PCI_SUCCESS);
 }