diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index f560814c557..f76f6e90f3b 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -780,11 +780,65 @@ static void pci_bus_dump_resources(struct pci_bus *bus)
 	}
 }
 
+static int __init pci_bus_get_depth(struct pci_bus *bus)
+{
+	int depth = 0;
+	struct pci_dev *dev;
+
+	list_for_each_entry(dev, &bus->devices, bus_list) {
+		int ret;
+		struct pci_bus *b = dev->subordinate;
+		if (!b)
+			continue;
+
+		ret = pci_bus_get_depth(b);
+		if (ret + 1 > depth)
+			depth = ret + 1;
+	}
+
+	return depth;
+}
+static int __init pci_get_max_depth(void)
+{
+	int depth = 0;
+	struct pci_bus *bus;
+
+	list_for_each_entry(bus, &pci_root_buses, node) {
+		int ret;
+
+		ret = pci_bus_get_depth(bus);
+		if (ret > depth)
+			depth = ret;
+	}
+
+	return depth;
+}
+
+/*
+ * first try will not touch pci bridge res
+ * second  and later try will clear small leaf bridge res
+ * will stop till to the max  deepth if can not find good one
+ */
 void __init
 pci_assign_unassigned_resources(void)
 {
 	struct pci_bus *bus;
+	int tried_times = 0;
+	enum release_type rel_type = leaf_only;
+	struct resource_list_x head, *list;
+	unsigned long type_mask = IORESOURCE_IO | IORESOURCE_MEM |
+				  IORESOURCE_PREFETCH;
+	unsigned long failed_type;
+	int max_depth = pci_get_max_depth();
+	int pci_try_num;
 
+	head.next = NULL;
+
+	pci_try_num = max_depth + 1;
+	printk(KERN_DEBUG "PCI: max bus depth: %d pci_try_num: %d\n",
+		 max_depth, pci_try_num);
+
+again:
 	/* Depth first, calculate sizes and alignments of all
 	   subordinate buses. */
 	list_for_each_entry(bus, &pci_root_buses, node) {
@@ -792,9 +846,65 @@ pci_assign_unassigned_resources(void)
 	}
 	/* Depth last, allocate resources and update the hardware. */
 	list_for_each_entry(bus, &pci_root_buses, node) {
-		pci_bus_assign_resources(bus);
-		pci_enable_bridges(bus);
+		__pci_bus_assign_resources(bus, &head);
 	}
+	tried_times++;
+
+	/* any device complain? */
+	if (!head.next)
+		goto enable_and_dump;
+	failed_type = 0;
+	for (list = head.next; list;) {
+		failed_type |= list->flags;
+		list = list->next;
+	}
+	/*
+	 * io port are tight, don't try extra
+	 * or if reach the limit, don't want to try more
+	 */
+	failed_type &= type_mask;
+	if ((failed_type == IORESOURCE_IO) || (tried_times >= pci_try_num)) {
+		free_failed_list(&head);
+		goto enable_and_dump;
+	}
+
+	printk(KERN_DEBUG "PCI: No. %d try to assign unassigned res\n",
+			 tried_times + 1);
+
+	/* third times and later will not check if it is leaf */
+	if ((tried_times + 1) > 2)
+		rel_type = whole_subtree;
+
+	/*
+	 * Try to release leaf bridge's resources that doesn't fit resource of
+	 * child device under that bridge
+	 */
+	for (list = head.next; list;) {
+		bus = list->dev->bus;
+		pci_bus_release_bridge_resources(bus, list->flags & type_mask,
+						  rel_type);
+		list = list->next;
+	}
+	/* restore size and flags */
+	for (list = head.next; list;) {
+		struct resource *res = list->res;
+
+		res->start = list->start;
+		res->end = list->end;
+		res->flags = list->flags;
+		if (list->dev->subordinate)
+			res->flags = 0;
+
+		list = list->next;
+	}
+	free_failed_list(&head);
+
+	goto again;
+
+enable_and_dump:
+	/* Depth last, update the hardware. */
+	list_for_each_entry(bus, &pci_root_buses, node)
+		pci_enable_bridges(bus);
 
 	/* dump the resource on buses */
 	list_for_each_entry(bus, &pci_root_buses, node) {