tty: tty_driver: document both {,__}tty_alloc_driver() properly

__tty_alloc_driver()'s kernel-doc needed some care: describe the return
value using the standard "Returns:", and use the new enum tty_driver_flag
for @flags.

Then, the tty_alloc_driver() macro was undocumented, but referenced many
times in the docs. Copy the docs from the above (except the @owner
parameter, obviously).

Signed-off-by: Jiri Slaby (SUSE) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Jiri Slaby (SUSE)

Documentation/driver-api/tty/tty_driver.rst

@@ -25,6 +25,8 @@ freed.
 For reference, both allocation and deallocation functions are explained here in
 detail:
 
+.. kernel-doc:: include/linux/tty_driver.h
+   :identifiers: tty_alloc_driver
 .. kernel-doc:: drivers/tty/tty_io.c
    :identifiers: __tty_alloc_driver tty_driver_kref_put
 

drivers/tty/tty_io.c

@@ -3329,10 +3329,12 @@ EXPORT_SYMBOL(tty_unregister_device);
  * __tty_alloc_driver - allocate tty driver
  * @lines: count of lines this driver can handle at most
  * @owner: module which is responsible for this driver
- * @flags: some of %TTY_DRIVER_ flags, will be set in driver->flags
+ * @flags: some of enum tty_driver_flag, will be set in driver->flags
  *
- * This should not be called directly, some of the provided macros should be
- * used instead. Use IS_ERR() and friends on @retval.
+ * This should not be called directly, tty_alloc_driver() should be used
+ * instead.
+ *
+ * Returns: struct tty_driver or a PTR-encoded error (use IS_ERR() and friends).
  */
 struct tty_driver *__tty_alloc_driver(unsigned int lines, struct module *owner,
 		unsigned long flags)

include/linux/tty_driver.h

@@ -564,7 +564,13 @@ struct tty_driver *tty_find_polling_driver(char *name, int *line);
 
 void tty_driver_kref_put(struct tty_driver *driver);
 
-/* Use TTY_DRIVER_* flags below */
+/**
+ * tty_alloc_driver - allocate tty driver
+ * @lines: count of lines this driver can handle at most
+ * @flags: some of enum tty_driver_flag, will be set in driver->flags
+ *
+ * Returns: struct tty_driver or a PTR-encoded error (use IS_ERR() and friends).
+ */
 #define tty_alloc_driver(lines, flags) \
 		__tty_alloc_driver(lines, THIS_MODULE, flags)