diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index e79bf2afd9be..a47ce3e974a2 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1293,22 +1293,19 @@ static void autoconfig(struct uart_8250_port *up)
 
 	serial_out(up, UART_FCR, UART_FCR_ENABLE_FIFO);
 
-	/* Assign this as it is to truncate any bits above 7.  */
-	scratch = serial_in(up, UART_IIR);
-
-	switch (scratch >> 6) {
-	case 0:
+	switch (serial_in(up, UART_IIR) & UART_IIR_FIFO_ENABLED) {
+	case UART_IIR_FIFO_ENABLED_8250:
 		autoconfig_8250(up);
 		break;
-	case 1:
-		port->type = PORT_UNKNOWN;
-		break;
-	case 2:
+	case UART_IIR_FIFO_ENABLED_16550:
 		port->type = PORT_16550;
 		break;
-	case 3:
+	case UART_IIR_FIFO_ENABLED_16550A:
 		autoconfig_16550a(up);
 		break;
+	default:
+		port->type = PORT_UNKNOWN;
+		break;
 	}
 
 #ifdef CONFIG_SERIAL_8250_RSA
diff --git a/include/uapi/linux/serial_reg.h b/include/uapi/linux/serial_reg.h
index bab3b39266cc..19aef5b0b049 100644
--- a/include/uapi/linux/serial_reg.h
+++ b/include/uapi/linux/serial_reg.h
@@ -44,6 +44,10 @@
 #define UART_IIR_RX_TIMEOUT	0x0c /* OMAP RX Timeout interrupt */
 #define UART_IIR_XOFF		0x10 /* OMAP XOFF/Special Character */
 #define UART_IIR_CTS_RTS_DSR	0x20 /* OMAP CTS/RTS/DSR Change */
+#define UART_IIR_FIFO_ENABLED	0xc0 /* FIFOs enabled / port type identification */
+#define  UART_IIR_FIFO_ENABLED_8250	0x00	/* 8250: no FIFO */
+#define  UART_IIR_FIFO_ENABLED_16550	0x80	/* 16550: (broken/unusable) FIFO */
+#define  UART_IIR_FIFO_ENABLED_16550A	0xc0	/* 16550A: FIFO enabled */
 
 #define UART_FCR	2	/* Out: FIFO Control Register */
 #define UART_FCR_ENABLE_FIFO	0x01 /* Enable the FIFO */