[PATCH v3 01/15] nvkm: add a kernel doc to introduce the GSP RPC

[Zhi Wang <zhiw@nvidia.com>]

In order to explain the name clean-ups in GSP RPC routines, a kernel
doc to explain the memory layout and terms is required.

Add a kernel doc to introduce the GSP RPC.

Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 .../gpu/drm/nouveau/nvkm/subdev/gsp/r535.c    | 46 +++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
index a4b8381c4e3e..1a07c0191356 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
@@ -60,6 +60,52 @@
 #define GSP_MSG_MIN_SIZE GSP_PAGE_SIZE
 #define GSP_MSG_MAX_SIZE GSP_PAGE_MIN_SIZE * 16
 
+/**
+ * DOC: GSP message queue element
+ *
+ * https://github.com/NVIDIA/open-gpu-kernel-modules/blob/main/src/nvidia/inc/kernel/gpu/gsp/message_queue_priv.h
+ *
+ * The GSP command queue and status queue are message queues for the
+ * communication between software and GSP. The software submits the GSP
+ * RPC via the GSP command queue, GSP writes the status of the submitted
+ * RPC in the status queue.
+ *
+ * A GSP message queue element consists of three parts:
+ *
+ * - message element header (struct r535_gsp_msg), which mostly maintains
+ * the metadata for queuing the element.
+ *
+ * - RPC message header (struct nvfw_gsp_rpc), which maintains the info
+ * of the RPC. E.g., the RPC function number.
+ *
+ * - The payload, where the RPC message stays. E.g. the params of a
+ * specific RPC function. Some RPC functions also have their headers
+ * in the payload. E.g. rm_alloc, rm_control.
+ *
+ * The memory layout of a GSP message element can be illustrated below:
+ *
+ * +------------------------+
+ * | Message Element Header |
+ * |    (r535_gsp_msg)      |
+ * |                        |
+ * | (r535_gsp_msg.data)    |
+ * |          |             |
+ * |----------V-------------|
+ * |    GSP RPC Header      |
+ * |    (nvfw_gsp_rpc)      |
+ * |                        |
+ * | (nvfw_gsp_rpc.data)    |
+ * |          |             |
+ * |----------V-------------|
+ * |                        |
+ * |       Payload          |
+ * |                        |
+ * |   header(optional)     |
+ * |        params          |
+ * +------------------------+
+ *
+ */
+
 struct r535_gsp_msg {
 	u8 auth_tag_buffer[16];
 	u8 aad_buffer[16];
-- 
2.34.1