api: allow tagging AT ports as GPS control

There are devices with multiple AT ports where only one of them is
supposed to be used for GNSS control (and data).

include/ModemManager-tags.h

@@ -129,6 +129,19 @@
  */
 #define ID_MM_PORT_TYPE_AT_SECONDARY "ID_MM_PORT_TYPE_AT_SECONDARY"
 
+/**
+ * ID_MM_PORT_TYPE_AT_GPS_CONTROL:
+ *
+ * This is a port-specific tag applied to TTYs that we know in advance
+ * are AT ports to be used for GPS control. Depending on the device,
+ * this may or may not mean the same port is also used fo GPS data.
+ *
+ * This tag will also proevent QCDM probing on the port.
+ *
+ * Since: 1.20
+ */
+#define ID_MM_PORT_TYPE_AT_GPS_CONTROL "ID_MM_PORT_TYPE_AT_GPS_CONTROL"
+
 /**
  * ID_MM_PORT_TYPE_AT_PPP:
  *

src/mm-base-modem.c

@@ -391,6 +391,13 @@ base_modem_internal_grab_port (MMBaseModem         *self,
                 mm_obj_dbg (port, "AT port flagged as PPP");
                 at_pflags = MM_PORT_SERIAL_AT_FLAG_PPP;
             }
+
+            /* Additionally, the ports may also be flagged as GPS control explicitly, if there is
+             * one specific port to be used for that purpose */
+            if (mm_kernel_device_get_property_as_boolean (kernel_device, ID_MM_PORT_TYPE_AT_GPS_CONTROL)) {
+                mm_obj_dbg (port, "AT port flagged as GPS control");
+                at_pflags = MM_PORT_SERIAL_AT_FLAG_GPS_CONTROL;
+            }
         }
         /* The plugin may specify NONE_NO_GENERIC to avoid the generic
          * port type hints from being applied. */