firmware: imx: Skip return value check for some special SCU firmware APIs

The SCU firmware does NOT always have return value stored in message
header's function element even the API has response data, those special
APIs are defined as void function in SCU firmware, so they should be
treated as return success always.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

drivers/firmware/imx/imx-scu.c

@@ -162,6 +162,7 @@ static int imx_scu_ipc_write(struct imx_sc_ipc *sc_ipc, void *msg)
  */
 int imx_scu_call_rpc(struct imx_sc_ipc *sc_ipc, void *msg, bool have_resp)
 {
+	uint8_t saved_svc, saved_func;
 	struct imx_sc_rpc_msg *hdr;
 	int ret;
 
@@ -171,8 +172,11 @@ int imx_scu_call_rpc(struct imx_sc_ipc *sc_ipc, void *msg, bool have_resp)
 	mutex_lock(&sc_ipc->lock);
 	reinit_completion(&sc_ipc->done);
 
-	if (have_resp)
+	if (have_resp) {
 		sc_ipc->msg = msg;
+		saved_svc = ((struct imx_sc_rpc_msg *)msg)->svc;
+		saved_func = ((struct imx_sc_rpc_msg *)msg)->func;
+	}
 	sc_ipc->count = 0;
 	ret = imx_scu_ipc_write(sc_ipc, msg);
 	if (ret < 0) {
@@ -191,6 +195,16 @@ int imx_scu_call_rpc(struct imx_sc_ipc *sc_ipc, void *msg, bool have_resp)
 		/* response status is stored in hdr->func field */
 		hdr = msg;
 		ret = hdr->func;
+		/*
+		 * Some special SCU firmware APIs do NOT have return value
+		 * in hdr->func, but they do have response data, those special
+		 * APIs are defined as void function in SCU firmware, so they
+		 * should be treated as return success always.
+		 */
+		if ((saved_svc == IMX_SC_RPC_SVC_MISC) &&
+			(saved_func == IMX_SC_MISC_FUNC_UNIQUE_ID ||
+			 saved_func == IMX_SC_MISC_FUNC_GET_BUTTON_STATUS))
+			ret = 0;
 	}
 
 out: