diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 67f7733..670511f 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -644,6 +644,9 @@ static int acpi_pci_root_start(struct acpi_device *device)
 		if (driver->add)
 			driver->add(root);
 
+	/* need to after hot-added ioapic is registered */
+	pci_enable_bridges(root->bus);
+
 	pci_bus_add_devices(root->bus);
 	mutex_unlock(&acpi_pci_root_lock);
 
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 460ac84..5975fd5 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1905,6 +1905,7 @@ unsigned int __ref pci_rescan_bus(struct pci_bus *bus)
 
 	max = pci_scan_child_bus(bus);
 	pci_assign_unassigned_bus_resources(bus);
+	pci_enable_bridges(bus);
 	pci_bus_add_devices(bus);
 
 	return max;
diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 56155c9..63cb3ba 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1566,6 +1566,4 @@ void pci_assign_unassigned_bus_resources(struct pci_bus *bus)
 	up_read(&pci_bus_sem);
 	__pci_bus_assign_resources(bus, &add_list, NULL);
 	BUG_ON(!list_empty(&add_list));
-
-	pci_enable_bridges(bus);
 }