drm/nouveau/nvkm: introduce new GSP reply policy NVKM_GSP_RPC_REPLY_POLL

Some GSP RPC commands need a new reply policy: "caller don't care about
the message content but want to make sure a reply is received". To
support this case, a new reply policy is introduced.

NV_VGPU_MSG_FUNCTION_ALLOC_MEMORY is a large GSP RPC command. The actual
required policy is NVKM_GSP_RPC_REPLY_POLL. This can be observed from the
dump of the GSP message queue. After the large GSP RPC command is issued,
GSP will write only an empty RPC header in the queue as the reply.

Without this change, the policy "receiving the entire message" is used
for NV_VGPU_MSG_FUNCTION_ALLOC_MEMORY. This causes the timeout of receiving
the returned GSP message in the suspend/resume path.

Introduce the new reply policy NVKM_GSP_RPC_REPLY_POLL, which waits for
the returned GSP message but discards it for the caller. Use the new policy
NVKM_GSP_RPC_REPLY_POLL on the GSP RPC command
NV_VGPU_MSG_FUNCTION_ALLOC_MEMORY.

Fixes: 50f2900 ("drm/nouveau: support handling the return of large GSP message")
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Ben Skeggs <bskeggs@nvidia.com>
Signed-off-by: Zhi Wang <zhiw@nvidia.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250227013554.8269-3-zhiw@nvidia.com

Author: zhiwang-nvidia

drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h

@@ -44,10 +44,14 @@ typedef void (*nvkm_gsp_event_func)(struct nvkm_gsp_event *, void *repv, u32 rep
  * NVKM_GSP_RPC_REPLY_RECV - If specified, wait and receive the entire GSP
  * RPC message after the GSP RPC command is issued.
  *
+ * NVKM_GSP_RPC_REPLY_POLL - If specified, wait for the specific reply and
+ * discard the reply before returning to the caller.
+ *
  */
 enum nvkm_gsp_rpc_reply_policy {
 	NVKM_GSP_RPC_REPLY_NOWAIT = 0,
 	NVKM_GSP_RPC_REPLY_RECV,
+	NVKM_GSP_RPC_REPLY_POLL,
 };
 
 struct nvkm_gsp {

drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c

@@ -602,6 +602,9 @@ r535_gsp_rpc_handle_reply(struct nvkm_gsp *gsp, u32 fn,
 		else
 			repv = reply;
 		break;
+	case NVKM_GSP_RPC_REPLY_POLL:
+		repv = r535_gsp_msg_recv(gsp, fn, 0);
+		break;
 	}
 
 	return repv;

drivers/gpu/drm/nouveau/nvkm/subdev/instmem/r535.c

@@ -105,7 +105,7 @@ fbsr_memlist(struct nvkm_gsp_device *device, u32 handle, enum nvkm_memory_target
 			rpc->pteDesc.pte_pde[i].pte = (phys >> 12) + i;
 	}
 
-	ret = nvkm_gsp_rpc_wr(gsp, rpc, NVKM_GSP_RPC_REPLY_RECV);
+	ret = nvkm_gsp_rpc_wr(gsp, rpc, NVKM_GSP_RPC_REPLY_POLL);
 	if (ret)
 		return ret;