base-bearer: stop connection status monitoring if no TTY available

On modems with a single TTY for both control and data, we cannot use
the TTY to load connection status once we're in connected mode:

    Connection through a plain serial AT port (ttyUSB2)
    (ttyUSB2): --> 'ATD*99***2#<CR>'
    (ttyUSB2): <-- '<CR><LF>CONNECT 100000000<CR><LF>'
    (ttyUSB2): port now connected
    Connected bearer '/org/freedesktop/ModemManager1/Bearer/0'
    Modem /org/freedesktop/ModemManager1/Modem/0: state changed (connecting -> connected)
    Simple connect state (8/8): All done
    checking if connected failed: Couldn't check current list of active PDP contexts: No AT port available to run command
    checking if connected failed: Couldn't check current list of active PDP contexts: No AT port available to run command
    checking if connected failed: Couldn't check current list of active PDP contexts: No AT port available to run command
    ...

So, disable connection monitoring right away if that situation is
detected:

    Connection through a plain serial AT port (ttyUSB2)
    (ttyUSB2): --> 'ATD*99***2#<CR>'
    (ttyUSB2): <-- '<CR><LF>CONNECT 100000000<CR><LF>'
    (ttyUSB2): port now connected
    Connected bearer '/org/freedesktop/ModemManager1/Bearer/0'
    Modem /org/freedesktop/ModemManager1/Modem/0: state changed (connecting -> connected)
    Simple connect state (8/8): All done
    Connection monitoring is unsupported by the device
    ...

https://bugs.freedesktop.org/show_bug.cgi?id=100376

src/mm-base-bearer.c

@@ -92,6 +92,8 @@ struct _MMBaseBearerPrivate {
 
     /* Connection status monitoring */
     guint connection_monitor_id;
+    /* Flag to specify whether connection monitoring is supported or not */
+    gboolean load_connection_status_unsupported;
 
     /*-- 3GPP specific --*/
     guint deferred_3gpp_unregistration_id;
@@ -162,7 +164,18 @@ load_connection_status_ready (MMBaseBearer *self,
 
     status = MM_BASE_BEARER_GET_CLASS (self)->load_connection_status_finish (self, res, &error);
     if (status == MM_BEARER_CONNECTION_STATUS_UNKNOWN) {
-        mm_warn ("checking if connected failed: %s", error->message);
+        /* Only warn if not reporting an "unsupported" error */
+        if (!g_error_matches (error, MM_CORE_ERROR, MM_CORE_ERROR_UNSUPPORTED)) {
+            mm_warn ("checking if connected failed: %s", error->message);
+            g_error_free (error);
+            return;
+        }
+
+        /* If we're being told that connection monitoring is unsupported, just
+         * ignore the error and remove the timeout. */
+        mm_dbg ("Connection monitoring is unsupported by the device");
+        self->priv->load_connection_status_unsupported = TRUE;
+        connection_monitor_stop (self);
         g_error_free (error);
         return;
     }
@@ -176,7 +189,7 @@ load_connection_status_ready (MMBaseBearer *self,
 static gboolean
 connection_monitor_cb (MMBaseBearer *self)
 {
-    /* If the implementation knows how to update stat values, run it */
+    /* If the implementation knows how to load connection status, run it */
     MM_BASE_BEARER_GET_CLASS (self)->load_connection_status (
             self,
             (GAsyncReadyCallback)load_connection_status_ready,
@@ -192,6 +205,9 @@ connection_monitor_start (MMBaseBearer *self)
         !MM_BASE_BEARER_GET_CLASS (self)->load_connection_status_finish)
         return;
 
+    if (self->priv->load_connection_status_unsupported)
+        return;
+
     /* Schedule */
     g_assert (!self->priv->connection_monitor_id);
     self->priv->connection_monitor_id = g_timeout_add_seconds (BEARER_CONNECTION_MONITOR_TIMEOUT,

src/mm-broadband-bearer.c

@@ -1992,30 +1992,45 @@ load_connection_status (MMBaseBearer        *self,
                         GAsyncReadyCallback  callback,
                         gpointer             user_data)
 {
-    GTask       *task;
-    MMBaseModem *modem = NULL;
+    GTask          *task;
+    MMBaseModem    *modem = NULL;
+    MMPortSerialAt *port;
 
     task = g_task_new (self, NULL, callback, user_data);
 
-    if (!MM_BROADBAND_BEARER (self)->priv->cid) {
-        g_task_return_new_error (task, MM_CORE_ERROR, MM_CORE_ERROR_FAILED,
-                                 "Couldn't load connection status: cid not defined");
-        g_object_unref (task);
-        return;
-    }
-
     g_object_get (MM_BASE_BEARER (self),
                   MM_BASE_BEARER_MODEM, &modem,
                   NULL);
 
-    mm_base_modem_at_command (MM_BASE_MODEM (modem),
-                              "+CGACT?",
-                              3,
-                              FALSE,
-                              (GAsyncReadyCallback) cgact_periodic_query_ready,
-                              task);
+    /* If CID not defined, error out */
+    if (!MM_BROADBAND_BEARER (self)->priv->cid) {
+        g_task_return_new_error (task, MM_CORE_ERROR, MM_CORE_ERROR_FAILED,
+                                 "Couldn't load connection status: cid not defined");
+        g_object_unref (task);
+        goto out;
+    }
 
-    g_object_unref (modem);
+    /* If no control port available, error out */
+    port = mm_base_modem_peek_best_at_port (modem, NULL);
+    if (!port) {
+        g_task_return_new_error (task, MM_CORE_ERROR, MM_CORE_ERROR_UNSUPPORTED,
+                                 "Couldn't load connection status: no control port available");
+        g_object_unref (task);
+        goto out;
+    }
+
+    mm_base_modem_at_command_full (MM_BASE_MODEM (modem),
+                                   port,
+                                   "+CGACT?",
+                                   3,
+                                   FALSE, /* allow cached */
+                                   FALSE, /* raw */
+                                   NULL, /* cancellable */
+                                   (GAsyncReadyCallback) cgact_periodic_query_ready,
+                                   task);
+
+out:
+    g_clear_object (&modem);
 }
 
 /*****************************************************************************/