ACPI / scan: Add second pass to acpi_bus_trim()

Make acpi_bus_trim() work in analogy with acpi_bus_scan() and carry
out two passes such that ACPI drivers will be detached from device
nodes being removed in the first pass and the device nodes themselves
will be removed in the second pass.

For this purpose split the driver unregistration out of
acpi_bus_remove() into a new routine, acpi_bus_device_detach(), that
will be executed by acpi_bus_trim() in the additional first pass as
a post-order callback.

This is necessary, because some ACPI drivers' .remove() routines
unregister struct device objects associated with the ACPI device
nodes being removed and that needs to happen while the ACPI
device nodes are still around (for example, in case they need to be
used for power management or similar things at that time).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>

drivers/acpi/scan.c

@@ -1374,22 +1374,6 @@ static int acpi_device_set_context(struct acpi_device *device)
 	return -ENODEV;
 }
 
-static acpi_status acpi_bus_remove(acpi_handle handle, u32 lvl_not_used,
-				   void *not_used, void **ret_not_used)
-{
-	struct acpi_device *dev = NULL;
-
-	if (acpi_bus_get_device(handle, &dev))
-		return AE_OK;
-
-	dev->removal_type = ACPI_BUS_REMOVAL_EJECT;
-	device_release_driver(&dev->dev);
-
-	acpi_device_unregister(dev);
-
-	return AE_OK;
-}
-
 static int acpi_add_single_object(struct acpi_device **child,
 				  acpi_handle handle, int type,
 				  unsigned long long sta, bool match_driver)
@@ -1642,8 +1626,38 @@ int acpi_bus_add(acpi_handle handle)
 }
 EXPORT_SYMBOL(acpi_bus_add);
 
+static acpi_status acpi_bus_device_detach(acpi_handle handle, u32 lvl_not_used,
+					  void *not_used, void **ret_not_used)
+{
+	struct acpi_device *device = NULL;
+
+	if (!acpi_bus_get_device(handle, &device)) {
+		device->removal_type = ACPI_BUS_REMOVAL_EJECT;
+		device_release_driver(&device->dev);
+	}
+	return AE_OK;
+}
+
+static acpi_status acpi_bus_remove(acpi_handle handle, u32 lvl_not_used,
+				   void *not_used, void **ret_not_used)
+{
+	struct acpi_device *device = NULL;
+
+	if (!acpi_bus_get_device(handle, &device))
+		acpi_device_unregister(device);
+
+	return AE_OK;
+}
+
 int acpi_bus_trim(struct acpi_device *start)
 {
+	/*
+	 * Execute acpi_bus_device_detach() as a post-order callback to detach
+	 * all ACPI drivers from the device nodes being removed.
+	 */
+	acpi_walk_namespace(ACPI_TYPE_ANY, start->handle, ACPI_UINT32_MAX, NULL,
+			    acpi_bus_device_detach, NULL, NULL);
+	acpi_bus_device_detach(start->handle, 0, NULL, NULL);
 	/*
 	 * Execute acpi_bus_remove() as a post-order callback to remove device
 	 * nodes in the given namespace scope.