gpu: nvgpu: add Doxygen documentation for rwsem

Add Doxygen documentation details for rwsem unit.

Jira NVGPU-2596

Change-Id: I9b385531d2524f6fc58d3e6ecccedf97258aed6d
Signed-off-by: ajesh <akv@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/2199573
GVS: Gerrit_Virtual_Submit
Reviewed-by: Philip Elcan <pelcan@nvidia.com>
Reviewed-by: Vijayakumar Subbu <vsubbu@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/include/nvgpu/posix/rwsem.h

@@ -26,6 +26,9 @@
 #include <pthread.h>
 
 struct nvgpu_rwsem {
+	/**
+	 * pthread_rwlock_t used internally to implement nvgpu rwsem.
+	 */
 	pthread_rwlock_t rw_sem;
 };
 

drivers/gpu/nvgpu/include/nvgpu/rwsem.h

@@ -37,10 +37,53 @@
  */
 struct nvgpu_rwsem;
 
+/**
+ * @brief Initialize read write lock.
+ *
+ * @param rwsem [in]	Read,write lock to initalize.
+ *
+ * Initializes the read,write lock referenced by \a rwsem.
+ */
 void nvgpu_rwsem_init(struct nvgpu_rwsem *rwsem);
+
+/**
+ * @brief Acquire read lock.
+ *
+ * @param rwsem [in]	Read,write lock to be locked for read.
+ *
+ * Acquires a read lock on the read,write lock object referenced by \a rwsem.
+ * The calling thread acquires a read lock if no writer is holding the lock
+ * on \a rwsem.
+ */
 void nvgpu_rwsem_up_read(struct nvgpu_rwsem *rwsem);
+
+/**
+ * @brief Release read lock.
+ *
+ * @param rwsem [in]	Read,write lock to be released.
+ *
+ * Releases the lock held on \a rwsem. To be used to release a read lock.
+ */
 void nvgpu_rwsem_down_read(struct nvgpu_rwsem *rwsem);
+
+/**
+ * @brief Acquire write lock.
+ *
+ * @param rwsem [in]	Read,write lock to be locked for write.
+ *
+ * Acquires the write lock on \a rwsem. The calling thread acquires write lock
+ * if no other thread is holding a lock on rwsem.
+ */
 void nvgpu_rwsem_up_write(struct nvgpu_rwsem *rwsem);
+
+/**
+ * @brief Release the write lock.
+ *
+ * @param rwsem [in]	Read,write lock to be released.
+ *
+ * Releases the write lock held on \a rwsem. To be used to release a write
+ * lock.
+ */
 void nvgpu_rwsem_down_write(struct nvgpu_rwsem *rwsem);
 
 #endif /* NVGPU_RWSEM_H */