Additions to the Serial UART API (#22953)

- Added an empty constructor, setPort, and validatePort functions for Serial API
- Changed GPS to not allocate Serial object dynamically
- Moved access check on serial port name into the Serial API
- Improved the Qurt platform validatePort Serial function to implement a more rigorous check. Added safety check
to the setPort Serial function to make sure it isn't called after the port has been already opened.

platforms/qurt/src/px4/SerialImpl.cpp

@@ -48,9 +48,8 @@ SerialImpl::SerialImpl(const char *port, uint32_t baudrate, ByteSize bytesize, P
 	_stopbits(stopbits),
 	_flowcontrol(flowcontrol)
 {
-	if (port) {
-		strncpy(_port, port, sizeof(_port) - 1);
-		_port[sizeof(_port) - 1] = '\0';
+	if (validatePort(port)) {
+		setPort(port);
 
 	} else {
 		_port[0] = 0;
@@ -117,6 +116,11 @@ bool SerialImpl::open()
 		return false;
 	}
 
+	if (!validatePort(_port)) {
+		PX4_ERR("Invalid port %s", _port);
+		return false;
+	}
+
 	// qurt_uart_open will check validity of port and baudrate
 	int serial_fd = qurt_uart_open(_port, _baudrate);
 
@@ -256,6 +260,27 @@ const char *SerialImpl::getPort() const
 	return _port;
 }
 
+bool SerialImpl::validatePort(const char *port)
+{
+	return (qurt_uart_get_port(port) >= 0);
+}
+
+bool SerialImpl::setPort(const char *port)
+{
+	if (_open) {
+		PX4_ERR("Cannot set port after port has already been opened");
+		return false;
+	}
+
+	if (validatePort(port)) {
+		strncpy(_port, port, sizeof(_port) - 1);
+		_port[sizeof(_port) - 1] = '\0';
+		return true;
+	}
+
+	return false;
+}
+
 uint32_t SerialImpl::getBaudrate() const
 {
 	return _baudrate;