[PATCH v2 1/5] nouveau/gsp/rpc: Document RPC function return value contracts

[Hongling Zeng <zenghongling@kylinos.cn>]

Add kernel-doc comments to document the return value semantics of
RPC functions in r535/rpc.c. This clarifies which functions can return
NULL, error pointers, or both, helping maintainers validate future
changes.

Return value analysis:
- r535_gsp_msgq_peek(): Never returns NULL
- r535_gsp_msgq_recv_one_elem(): Never returns NULL
- r535_gsp_msgq_recv(): CAN return NULL (when RPC length invalid)
- r535_gsp_msg_recv(): CAN return NULL (queue drained/no matching message)
- r535_gsp_rpc_get(): Never returns NULL
- r535_gsp_rpc_handle_reply(): CAN return NULL (NOWAIT/NOSEQ policies)
- r535_gsp_rpc_send(): CAN return NULL (via handle_reply)
- r535_gsp_rpc_push(): CAN return NULL (via handle_reply)

Signed-off-by: Hongling Zeng <zenghongling@kylinos.cn>
---
 .../drm/nouveau/nvkm/subdev/gsp/rm/r535/rpc.c | 75 +++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/rpc.c b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/rpc.c
index 3ca3de8f4340..7dd43fa38c41 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/rpc.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/rpc.c
@@ -204,6 +204,15 @@ r535_gsp_msgq_get_entry(struct nvkm_gsp *gsp)
  *   The user is responsible for freeing the memory allocated for the GSP
  *   message pages after they have been processed.
  */
+/**
+ * r535_gsp_msgq_peek - Peek at next message in GSP command queue
+ * @gsp: GSP device
+ * @gsp_rpc_len: Expected RPC length
+ * @retries: Retry counter
+ *
+ * Return: Pointer to RPC message on success, or ERR_PTR() on error.
+ *         Never returns NULL.
+ */
 static void *
 r535_gsp_msgq_peek(struct nvkm_gsp *gsp, u32 gsp_rpc_len, int *retries)
 {
@@ -229,6 +238,14 @@ struct r535_gsp_msg_info {
 static void
 r535_gsp_msg_dump(struct nvkm_gsp *gsp, struct nvfw_gsp_rpc *msg, int lvl);
 
+/**
+ * r535_gsp_msgq_recv_one_elem - Receive one message element from GSP queue
+ * @gsp: GSP device
+ * @info: Message queue information
+ *
+ * Return: Pointer to received buffer on success, or ERR_PTR() on error.
+ *         Never returns NULL.
+ */
 static void *
 r535_gsp_msgq_recv_one_elem(struct nvkm_gsp *gsp,
 			    struct r535_gsp_msg_info *info)
@@ -283,6 +300,15 @@ r535_gsp_msgq_recv_one_elem(struct nvkm_gsp *gsp,
 	return buf;
 }
 
+/**
+ * r535_gsp_msgq_recv - Receive RPC message(s) from GSP queue
+ * @gsp: GSP device
+ * @gsp_rpc_len: Expected RPC length
+ * @retries: Retry counter
+ *
+ * Return: Pointer to received buffer on success, ERR_PTR() on error,
+ *         or NULL if RPC length is invalid.
+ */
 static void *
 r535_gsp_msgq_recv(struct nvkm_gsp *gsp, u32 gsp_rpc_len, int *retries)
 {
@@ -450,6 +476,15 @@ r535_gsp_msg_dump(struct nvkm_gsp *gsp, struct nvfw_gsp_rpc *msg, int lvl)
 	}
 }
 
+/**
+ * r535_gsp_msg_recv - Receive RPC message from GSP message queue
+ * @gsp: GSP device
+ * @fn: Expected RPC function number (0 to accept any)
+ * @gsp_rpc_len: Expected RPC length
+ *
+ * Return: Pointer to RPC message on success, ERR_PTR() on error,
+ *         or NULL if queue is drained or no matching message found.
+ */
 struct nvfw_gsp_rpc *
 r535_gsp_msg_recv(struct nvkm_gsp *gsp, int fn, u32 gsp_rpc_len)
 {
@@ -547,6 +582,17 @@ r535_gsp_rpc_poll(struct nvkm_gsp *gsp, u32 fn)
 	return 0;
 }
 
+/**
+ * r535_gsp_rpc_handle_reply - Handle RPC reply based on policy
+ * @gsp: GSP device
+ * @fn: RPC function number
+ * @policy: Reply policy (NOWAIT, NOSEQ, RECV, or POLL)
+ * @gsp_rpc_len: Expected RPC length
+ *
+ * Return: NULL when policy is NOWAIT or NOSEQ (no reply expected),
+ *         pointer to reply data on success, ERR_PTR() on error,
+ *         or NULL if no message available.
+ */
 static void *
 r535_gsp_rpc_handle_reply(struct nvkm_gsp *gsp, u32 fn,
 			  enum nvkm_gsp_rpc_reply_policy policy,
@@ -574,6 +620,16 @@ r535_gsp_rpc_handle_reply(struct nvkm_gsp *gsp, u32 fn,
 	return repv;
 }
 
+/**
+ * r535_gsp_rpc_send - Send RPC message and handle reply
+ * @gsp: GSP device
+ * @payload: RPC payload to send
+ * @policy: Reply policy (NOWAIT, NOSEQ, RECV, or POLL)
+ * @gsp_rpc_len: Expected RPC length for reply
+ *
+ * Return: NULL if policy is NOWAIT/NOSEQ (no reply expected),
+ *         pointer to reply data on success, or ERR_PTR() on error.
+ */
 static void *
 r535_gsp_rpc_send(struct nvkm_gsp *gsp, void *payload,
 		  enum nvkm_gsp_rpc_reply_policy policy, u32 gsp_rpc_len)
@@ -601,6 +657,15 @@ r535_gsp_rpc_send(struct nvkm_gsp *gsp, void *payload,
 	return r535_gsp_rpc_handle_reply(gsp, fn, policy, gsp_rpc_len);
 }
 
+/**
+ * r535_gsp_rpc_get - Allocate and initialize an RPC message
+ * @gsp: GSP device
+ * @fn: RPC function number
+ * @payload_size: Size of the payload
+ *
+ * Return: Pointer to RPC payload data on success, or ERR_PTR() on error.
+ *         Never returns NULL.
+ */
 static void
 r535_gsp_rpc_done(struct nvkm_gsp *gsp, void *repv)
 {
@@ -628,6 +693,16 @@ r535_gsp_rpc_get(struct nvkm_gsp *gsp, u32 fn, u32 payload_size)
 	return rpc->data;
 }
 
+/**
+ * r535_gsp_rpc_push - Push RPC message to GSP and wait for reply
+ * @gsp: GSP device
+ * @payload: RPC payload to send
+ * @policy: Reply policy (NOWAIT, NOSEQ, RECV, or POLL)
+ * @gsp_rpc_len: Expected RPC length in the reply
+ *
+ * Return: NULL when policy is NOWAIT/NOSEQ (no reply expected),
+ *         pointer to reply data on success, or ERR_PTR() on error.
+ */
 static void *
 r535_gsp_rpc_push(struct nvkm_gsp *gsp, void *payload,
 		  enum nvkm_gsp_rpc_reply_policy policy, u32 gsp_rpc_len)
-- 
2.25.1