driver-core: document ERR_PTR() return values

A number of functions in the driver core return ERR_PTR() values on
error. Document this in the kernel-doc of the functions.
Signed-off-by: NJani Nikula <ext-jani.1.nikula@nokia.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/base/class.c

@@ -219,6 +219,8 @@ static void class_create_release(struct class *cls)
  * This is used to create a struct class pointer that can then be used
  * in calls to device_create().
  *
+ * Returns &struct class pointer on success, or ERR_PTR() on error.
+ *
  * Note, the pointer created here is to be destroyed when finished by
  * making a call to class_destroy().
  */

drivers/base/core.c

@@ -1345,6 +1345,8 @@ static void root_device_release(struct device *dev)
  * 'module' symlink which points to the @owner directory
  * in sysfs.
  *
+ * Returns &struct device pointer on success, or ERR_PTR() on error.
+ *
  * Note: You probably want to use root_device_register().
  */
 struct device *__root_device_register(const char *name, struct module *owner)
@@ -1432,6 +1434,8 @@ static void device_create_release(struct device *dev)
  * Any further sysfs files that might be required can be created using this
  * pointer.
  *
+ * Returns &struct device pointer on success, or ERR_PTR() on error.
+ *
  * Note: the struct class passed to this function must have previously
  * been created with a call to class_create().
  */
@@ -1492,6 +1496,8 @@ EXPORT_SYMBOL_GPL(device_create_vargs);
  * Any further sysfs files that might be required can be created using this
  * pointer.
  *
+ * Returns &struct device pointer on success, or ERR_PTR() on error.
+ *
  * Note: the struct class passed to this function must have previously
  * been created with a call to class_create().
  */

drivers/base/platform.c

@@ -362,6 +362,8 @@ EXPORT_SYMBOL_GPL(platform_device_unregister);
  * enumeration tasks, they don't fully conform to the Linux driver model.
  * In particular, when such drivers are built as modules, they can't be
  * "hotplugged".
+ *
+ * Returns &struct platform_device pointer on success, or ERR_PTR() on error.
  */
 struct platform_device *platform_device_register_simple(const char *name,
 							int id,
@@ -408,6 +410,8 @@ EXPORT_SYMBOL_GPL(platform_device_register_simple);
  * allocated for the device allows drivers using such devices to be
  * unloaded without waiting for the last reference to the device to be
  * dropped.
+ *
+ * Returns &struct platform_device pointer on success, or ERR_PTR() on error.
  */
 struct platform_device *platform_device_register_data(
 		struct device *parent,
@@ -559,6 +563,8 @@ EXPORT_SYMBOL_GPL(platform_driver_probe);
  *
  * Use this in legacy-style modules that probe hardware directly and
  * register a single platform device and corresponding platform driver.
+ *
+ * Returns &struct platform_device pointer on success, or ERR_PTR() on error.
  */
 struct platform_device * __init_or_module platform_create_bundle(
 			struct platform_driver *driver,