diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index cd06c84..44c42ae 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -689,6 +689,34 @@ static void pci_fixup_parent_subordinate_busnr(struct pci_bus *child, int max)
 	}
 }
 
+static void __devinit pci_bus_extend_top(struct pci_bus *parent,
+		 long size, struct resource *parent_res)
+{
+	struct resource *res;
+
+	if (!size)
+		return;
+
+	while (parent) {
+		res = &parent->busn_res;
+		if (res == parent_res)
+			break;
+		pci_write_config_byte(parent->self, PCI_SUBORDINATE_BUS,
+					 parent->busn_res.end);
+		dev_printk(KERN_DEBUG, &parent->dev,
+				"busn_res: %s %02lx to %pR\n",
+				(size > 0) ? "extended" : "shrunk",
+				abs(size), res);
+		parent = parent->parent;
+	}
+}
+
+static void __devinit pci_bus_shrink_top(struct pci_bus *parent,
+		 long size, struct resource *parent_res)
+{
+	pci_bus_extend_top(parent, -size, parent_res);
+}
+
 /*
  * If it's a bridge, configure it and scan the bus behind it.
  * For CardBus bridges, we don't scan behind as the devices will