Index: linux-2.6/drivers/pci/setup-bus.c
===================================================================
--- linux-2.6.orig/drivers/pci/setup-bus.c
+++ linux-2.6/drivers/pci/setup-bus.c
@@ -810,11 +810,69 @@ static void pci_bus_dump_resources(struc
 	}
 }
 
+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 try will clear small leaf bridge res
+ * third try will clear related bridge: some aggressive
+ */
+int pci_try_num = 1;
 void __init
 pci_assign_unassigned_resources(void)
 {
 	struct pci_bus *bus;
+	int tried_times = 0;
+	int check_leaf = 1;
+	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();
 
+	head.next = NULL;
+
+	if (pci_try_num > 1) {
+		if (max_depth + 1 > pci_try_num)
+			pci_try_num = max_depth + 1;
+	}
+
+	printk(KERN_DEBUG "PCI: max 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) {
@@ -822,7 +880,64 @@ 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_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)
+		check_leaf = 0;
+
+	/*
+	 * 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_unused_bridge_res(bus, list->flags & type_mask,
+						  check_leaf);
+		list = list->next;
+	}
+	/* retore 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);
 	}
 
Index: linux-2.6/drivers/pci/pci.c
===================================================================
--- linux-2.6.orig/drivers/pci/pci.c
+++ linux-2.6/drivers/pci/pci.c
@@ -2777,6 +2777,11 @@ static int __init pci_setup(char *str)
 				pci_no_aer();
 			} else if (!strcmp(str, "nodomains")) {
 				pci_no_domains();
+			} else if (!strncmp(str, "try=", 4)) {
+				int try_num = memparse(str + 4, &str);
+
+				if (try_num > 0 && try_num < 16)
+					pci_try_num = try_num;
 			} else if (!strncmp(str, "cbiosize=", 9)) {
 				pci_cardbus_io_size = memparse(str + 9, &str);
 			} else if (!strncmp(str, "cbmemsize=", 10)) {
Index: linux-2.6/drivers/pci/pci.h
===================================================================
--- linux-2.6.orig/drivers/pci/pci.h
+++ linux-2.6/drivers/pci/pci.h
@@ -203,6 +203,8 @@ static inline int pci_ari_enabled(struct
 	return bus->self && bus->self->ari_enabled;
 }
 
+extern int pci_try_num;
+
 #ifdef CONFIG_PCI_QUIRKS
 extern int pci_is_reassigndev(struct pci_dev *dev);
 resource_size_t pci_specified_resource_alignment(struct pci_dev *dev);
