spi: fix kernel-doc warnings about missing return desc in spi.c

When building docs with make htmldocs, warnings about not having
a description for the return value are reported, i.e:

warning: No description found for return value of 'spi_register_driver'

Fix these by following the kernel-doc conventions explained in
Documentation/kernel-doc-nano-HOWTO.txt.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -378,6 +378,8 @@ static void spi_drv_shutdown(struct device *dev)
  * spi_register_driver - register a SPI driver
  * @sdrv: the driver to register
  * Context: can sleep
+ *
+ * Return: zero on success, else a negative error code.
  */
 int spi_register_driver(struct spi_driver *sdrv)
 {
@@ -429,7 +431,7 @@ static DEFINE_MUTEX(board_lock);
  * needs to discard the spi_device without adding it, then it should
  * call spi_dev_put() on it.
  *
- * Returns a pointer to the new device, or NULL.
+ * Return: a pointer to the new device, or NULL.
  */
 struct spi_device *spi_alloc_device(struct spi_master *master)
 {
@@ -488,7 +490,7 @@ static int spi_dev_check(struct device *dev, void *data)
  * Companion function to spi_alloc_device.  Devices allocated with
  * spi_alloc_device can be added onto the spi bus with this function.
  *
- * Returns 0 on success; negative errno on failure
+ * Return: 0 on success; negative errno on failure
  */
 int spi_add_device(struct spi_device *spi)
 {
@@ -561,7 +563,7 @@ EXPORT_SYMBOL_GPL(spi_add_device);
  * this is exported so that for example a USB or parport based adapter
  * driver could add devices (which it would learn about out-of-band).
  *
- * Returns the new device, or NULL.
+ * Return: the new device, or NULL.
  */
 struct spi_device *spi_new_device(struct spi_master *master,
 				  struct spi_board_info *chip)
@@ -633,6 +635,8 @@ static void spi_match_master_to_boardinfo(struct spi_master *master,
  *
  * The board info passed can safely be __initdata ... but be careful of
  * any embedded pointers (platform_data, etc), they're copied as-is.
+ *
+ * Return: zero on success, else a negative error code.
  */
 int spi_register_board_info(struct spi_board_info const *info, unsigned n)
 {
@@ -1210,6 +1214,8 @@ static int spi_init_queue(struct spi_master *master)
  *
  * If there are more messages in the queue, the next message is returned from
  * this call.
+ *
+ * Return: the next message in the queue, else NULL if the queue is empty.
  */
 struct spi_message *spi_get_next_queued_message(struct spi_master *master)
 {
@@ -1373,6 +1379,8 @@ static int __spi_queued_transfer(struct spi_device *spi,
  * spi_queued_transfer - transfer function for queued transfers
  * @spi: spi device which is requesting transfer
  * @msg: spi message which is to handled is queued to driver queue
+ *
+ * Return: zero on success, else a negative error code.
  */
 static int spi_queued_transfer(struct spi_device *spi, struct spi_message *msg)
 {
@@ -1672,12 +1680,13 @@ static struct class spi_master_class = {
  * only ones directly touching chip registers.  It's how they allocate
  * an spi_master structure, prior to calling spi_register_master().
  *
- * This must be called from context that can sleep.  It returns the SPI
- * master structure on success, else NULL.
+ * This must be called from context that can sleep.
  *
  * The caller is responsible for assigning the bus number and initializing
  * the master's methods before calling spi_register_master(); and (after errors
  * adding the device) calling spi_master_put() to prevent a memory leak.
+ *
+ * Return: the SPI master structure on success, else NULL.
  */
 struct spi_master *spi_alloc_master(struct device *dev, unsigned size)
 {
@@ -1761,6 +1770,8 @@ static int of_spi_register_master(struct spi_master *master)
  * success, else a negative error code (dropping the master's refcount).
  * After a successful return, the caller is responsible for calling
  * spi_unregister_master().
+ *
+ * Return: zero on success, else a negative error code.
  */
 int spi_register_master(struct spi_master *master)
 {
@@ -1854,6 +1865,8 @@ static void devm_spi_unregister(struct device *dev, void *res)
  *
  * Register a SPI device as with spi_register_master() which will
  * automatically be unregister
+ *
+ * Return: zero on success, else a negative error code.
  */
 int devm_spi_register_master(struct device *dev, struct spi_master *master)
 {
@@ -1959,6 +1972,8 @@ static int __spi_master_match(struct device *dev, const void *data)
  * arch init time.  It returns a refcounted pointer to the relevant
  * spi_master (which the caller must release), or NULL if there is
  * no such master registered.
+ *
+ * Return: the SPI master structure on success, else NULL.
  */
 struct spi_master *spi_busnum_to_master(u16 bus_num)
 {
@@ -2012,6 +2027,8 @@ static int __spi_validate_bits_per_word(struct spi_master *master, u8 bits_per_w
  * that the underlying controller or its driver does not support.  For
  * example, not all hardware supports wire transfers using nine bit words,
  * LSB-first wire encoding, or active-high chipselects.
+ *
+ * Return: zero on success, else a negative error code.
  */
 int spi_setup(struct spi_device *spi)
 {
@@ -2230,6 +2247,8 @@ static int __spi_async(struct spi_device *spi, struct spi_message *message)
  * no other spi_message queued to that device will be processed.
  * (This rule applies equally to all the synchronous transfer calls,
  * which are wrappers around this core asynchronous primitive.)
+ *
+ * Return: zero on success, else a negative error code.
  */
 int spi_async(struct spi_device *spi, struct spi_message *message)
 {
@@ -2282,6 +2301,8 @@ EXPORT_SYMBOL_GPL(spi_async);
  * no other spi_message queued to that device will be processed.
  * (This rule applies equally to all the synchronous transfer calls,
  * which are wrappers around this core asynchronous primitive.)
+ *
+ * Return: zero on success, else a negative error code.
  */
 int spi_async_locked(struct spi_device *spi, struct spi_message *message)
 {
@@ -2397,7 +2418,7 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
  * Also, the caller is guaranteeing that the memory associated with the
  * message will not be freed before this call returns.
  *
- * It returns zero on success, else a negative error code.
+ * Return: zero on success, else a negative error code.
  */
 int spi_sync(struct spi_device *spi, struct spi_message *message)
 {
@@ -2419,7 +2440,7 @@ EXPORT_SYMBOL_GPL(spi_sync);
  * SPI bus. It has to be preceded by a spi_bus_lock call. The SPI bus must
  * be released by a spi_bus_unlock call when the exclusive access is over.
  *
- * It returns zero on success, else a negative error code.
+ * Return: zero on success, else a negative error code.
  */
 int spi_sync_locked(struct spi_device *spi, struct spi_message *message)
 {
@@ -2440,7 +2461,7 @@ EXPORT_SYMBOL_GPL(spi_sync_locked);
  * exclusive access is over. Data transfer must be done by spi_sync_locked
  * and spi_async_locked calls when the SPI bus lock is held.
  *
- * It returns zero on success, else a negative error code.
+ * Return: always zero.
  */
 int spi_bus_lock(struct spi_master *master)
 {
@@ -2469,7 +2490,7 @@ EXPORT_SYMBOL_GPL(spi_bus_lock);
  * This call releases an SPI bus lock previously obtained by an spi_bus_lock
  * call.
  *
- * It returns zero on success, else a negative error code.
+ * Return: always zero.
  */
 int spi_bus_unlock(struct spi_master *master)
 {
@@ -2504,6 +2525,8 @@ static u8	*buf;
  * portable code should never use this for more than 32 bytes.
  * Performance-sensitive or bulk transfer code should instead use
  * spi_{async,sync}() calls with dma-safe buffers.
+ *
+ * Return: zero on success, else a negative error code.
  */
 int spi_write_then_read(struct spi_device *spi,
 		const void *txbuf, unsigned n_tx,