doxygen: remove @return command if function return void

When doxygen is upgraded to v1.9.8 (on ubuntu 24.04), doxygen
reports: "doxygen error: found documented return type for xxx
that does not return anything" for those functions which return
void but declare "@return" in doxygen comment.

Solution: remove "@return" for those cases, and update
guide document for how to write doxgen comment for functions.

Signed-off-by: Chen Wang <[email protected]>

Author: unicornx

components/drivers/audio/dev_audio.c

@@ -751,8 +751,6 @@ int rt_audio_samplerate_to_speed(rt_uint32_t bitValue)
  * See _audio_send_replay_frame for details
  *
  * @param[in] audio pointer to audio device
- *
- * @return void
  */
 void rt_audio_tx_complete(struct rt_audio_device *audio)
 {
@@ -768,8 +766,6 @@ void rt_audio_tx_complete(struct rt_audio_device *audio)
  * @param[in] pbuf pointer ro data to be received
  *
  * @param[in] len buffer size
- *
- * @return void
  */
 void rt_audio_rx_done(struct rt_audio_device *audio, rt_uint8_t *pbuf, rt_size_t len)
 {

components/drivers/include/drivers/dev_can.h

@@ -709,8 +709,6 @@ rt_err_t rt_hw_can_register(struct rt_can_device    *can,
  *
  * @param[in] can    A pointer to the CAN device structure.
  * @param[in] event  The interrupt event mask, indicating the cause of the interrupt.
- *
- * @return void
  */
 void rt_hw_can_isr(struct rt_can_device *can, int event);
 

documentation/0.doxygen/example/src/function.c

@@ -33,10 +33,12 @@
  *
  * To documenting for functions, a comment block before the function
  * declaraion/definition is recommended to describe the general information
- * of the function. In the comment block, a `@brief` is required, a `@return`
- * is also required no matter if the function return values or not. `@param` is
- * required if any, and if it is provided, direction [in]/[out]/[in,out] should
- * be provide together. Other commands (such as `@note`) are optional.
+ * of the function. In the comment block, a `@brief` is required. A `@return`
+ * is also required if the function is intended to return a value, otherwise
+ * if the function is implemented with a void return type, `@return` is not
+ * required. `@param` is required if any, and if it is provided,
+ * direction [in]/[out]/[in,out] should be provide together. Other commands
+ * (such as `@note`) are optional.
  *
  * If you feel that the description of `@brief` is not enough, you
  * can add a detailed description part, which is also optional.
@@ -72,8 +74,6 @@
  *
  * @param[in] b Description of param b
  *
- * @return void
- *
  * @note This is a note for this structure, blah blah blah...
  */
 void doxygen_example_func_foo(int a, int b)