app: Handle PPP pipes properly

In case of AT#XCMUX command is used, PPP is permanently attached to
one of the pipes. PPP module keeps this pipe until CMUX stops.

Signed-off-by: Seppo Takalo <seppo.takalo@nordicsemi.no>

Author: SeppoTakalo

app/src/sm_cmux.c

@@ -122,11 +122,13 @@ static void stop_work_fn(struct k_work *work)
 {
 	ARG_UNUSED(work);
 
-	/* Will stop the UART when calling the close_pipe() function. */
 	if (sm_cmux_is_started()) {
 		modem_cmux_release(&cmux.instance);
 
 		cmux.at_channel = 0;
+		if (IS_ENABLED(CONFIG_SM_PPP)) {
+			sm_ppp_detach();
+		}
 
 		/* Return AT host to UART pipe */
 		sm_at_host_set_pipe(sm_at_host_get_urc_ctx(), cmux.uart_pipe);

app/src/sm_ppp.c

@@ -33,6 +33,7 @@ bool sm_fwd_cgev_notifs;
 
 static struct net_if *ppp_iface;
 static bool sm_ppp_auto_start;
+static bool sm_ppp_keep_pipe_attached;
 static uint8_t ppp_data_buf[1500];
 static struct sockaddr_ll ppp_zephyr_dst_addr;
 
@@ -383,7 +384,7 @@ bool sm_ppp_is_stopped(void)
 
 static int ppp_stop(enum ppp_reason reason)
 {
-	bool restarting;
+	bool restarting = false;
 
 	if (ppp_state == PPP_STATE_STOPPED) {
 		LOG_INF("PPP already stopped");
@@ -392,14 +393,15 @@ static int ppp_stop(enum ppp_reason reason)
 
 	ppp_state = PPP_STATE_STOPPING;
 
-	switch (reason) {
-	case PPP_REASON_PEER_DISCONNECTED:
-	case PPP_REASON_CMD:
-		restarting = false;
-		break;
-	default:
-		restarting = true;
-		break;
+	if (sm_ppp_keep_pipe_attached) {
+		switch (reason) {
+		case PPP_REASON_NETWORK:
+		case PPP_REASON_ERROR:
+			restarting = true;
+			break;
+		default:
+			break;
+		}
 	}
 
 	if (!restarting) {
@@ -417,7 +419,7 @@ static int ppp_stop(enum ppp_reason reason)
 
 	modem_ppp_release(&ppp_module);
 
-	if (!restarting) {
+	if (!sm_ppp_keep_pipe_attached) {
 		/* Return the pipe back to AT host */
 		sm_at_host_attach(ppp_pipe);
 		ppp_pipe = NULL;
@@ -428,7 +430,6 @@ static int ppp_stop(enum ppp_reason reason)
 	close_ppp_sockets();
 
 	ppp_state = PPP_STATE_STOPPED;
-	ppp_pipe = NULL;
 	send_status_notification();
 
 	return 0;
@@ -839,4 +840,11 @@ void sm_ppp_attach(struct modem_pipe *pipe)
 		modem_pipe_release(pipe);
 	}
 	ppp_pipe = pipe;
+	sm_ppp_keep_pipe_attached = true;
+}
+
+void sm_ppp_detach(void)
+{
+	ppp_pipe = NULL;
+	sm_ppp_keep_pipe_attached = false;
 }

app/src/sm_ppp.h

@@ -15,7 +15,10 @@ extern bool sm_fwd_cgev_notifs;
 bool sm_ppp_is_stopped(void);
 void sm_ppp_set_auto_start(bool enable);
 
-/** Set the modem pipe for PPP communication */
+/** Set the permanent modem pipe for PPP communication */
 void sm_ppp_attach(struct modem_pipe *pipe);
 
+/** Detach the modem pipe from PPP communication */
+void sm_ppp_detach(void);
+
 #endif