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.

src/lib/drivers/device/qurt/uart.c

@@ -25,19 +25,32 @@ void configure_uart_callbacks(open_uart_func_t open_func,
 	}
 }
 
-int qurt_uart_open(const char *dev, speed_t speed)
+int qurt_uart_get_port(const char *dev)
 {
-	if (_callbacks_configured) {
+	if (dev != NULL) {
 		// Convert device string into a uart port number
 		char *endptr = NULL;
-		uint8_t port_number = (uint8_t) strtol(dev, &endptr, 10);
+		int port_number = strtol(dev, &endptr, 10);
 
 		if ((port_number == 0) && (endptr == dev)) {
 			PX4_ERR("Could not convert %s into a valid uart port number", dev);
 			return -1;
-		}
 
-		return _open_uart(port_number, speed);
+		} else {
+			return port_number;
+		}
+	}
+
+	return -1;
+}
+
+int qurt_uart_open(const char *dev, speed_t speed)
+{
+	int port_number = qurt_uart_get_port(dev);
+
+	if (_callbacks_configured && (port_number >= 0)) {
+
+		return _open_uart((uint8_t) port_number, speed);
 
 	} else {
 		PX4_ERR("Cannot open uart until callbacks have been configured");

src/lib/drivers/device/qurt/uart.h

@@ -7,6 +7,7 @@ extern "C" {
 #include <stdbool.h>
 #include <termios.h>
 
+int qurt_uart_get_port(const char *dev);
 int qurt_uart_open(const char *dev, speed_t speed);
 int qurt_uart_write(int fd, const char *buf, size_t len);
 int qurt_uart_read(int fd, char *buf, size_t len, uint32_t timeout_us);