[ringbuffer] 添加 ringbuffer 的接口注释

components/drivers/include/ipc/ringbuffer.h

@@ -5,6 +5,7 @@
  *
  * Change Logs:
  * Date           Author       Notes
+ * 2021-08-14     Jackistang   add commets for function inferface.
  */
 #ifndef RINGBUFFER_H__
 #define RINGBUFFER_H__
@@ -80,6 +81,13 @@ struct rt_ringbuffer* rt_ringbuffer_create(rt_uint16_t length);
 void rt_ringbuffer_destroy(struct rt_ringbuffer *rb);
 #endif
 
+/**
+ * @brief Get buffer size of the ringbuffer object.
+ * 
+ * @param rb        A pointer to the ringbuffer object.
+ * 
+ * @return  Buffer size.
+ */
 rt_inline rt_uint16_t rt_ringbuffer_get_size(struct rt_ringbuffer *rb)
 {
     RT_ASSERT(rb != RT_NULL);