diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c
index d35f1d24156c..f28d0633fe6b 100644
--- a/drivers/tty/serial/serial_port.c
+++ b/drivers/tty/serial/serial_port.c
@@ -173,6 +173,7 @@ EXPORT_SYMBOL(uart_remove_one_port);
  * The caller is responsible to initialize the following fields of the @port
  *   ->dev (must be valid)
  *   ->flags
+ *   ->iobase
  *   ->mapbase
  *   ->mapsize
  *   ->regshift (if @use_defaults is false)
@@ -214,7 +215,7 @@ static int __uart_read_properties(struct uart_port *port, bool use_defaults)
 	/* Read the registers I/O access type (default: MMIO 8-bit) */
 	ret = device_property_read_u32(dev, "reg-io-width", &value);
 	if (ret) {
-		port->iotype = UPIO_MEM;
+		port->iotype = port->iobase ? UPIO_PORT : UPIO_MEM;
 	} else {
 		switch (value) {
 		case 1: