USB: ftdi_sio: enable two UART ports on ST Microconnect Lite

commit 71d9a2b9 upstream.

The FT4232H used in the ST Micro Connect Lite has four hi-speed UART ports.
The first two ports are reserved for the JTAG interface.

We enable by default ports 2 and 3 as UARTs (where port 2 is a
conventional RS-232 UART)
Signed-off-by: Adrian Thomasset <adrian.thomasset@st.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/ftdi_sio.c

@@ -1855,8 +1855,11 @@ static int ftdi_8u2232c_probe(struct usb_serial *serial)
 }
 
 /*
- * First and second port on STMCLiteadaptors is reserved for JTAG interface
- * and the forth port for pio
+ * First two ports on JTAG adaptors using an FT4232 such as STMicroelectronics's
+ * ST Micro Connect Lite are reserved for JTAG or other non-UART interfaces and
+ * can be accessed from userspace.
+ * The next two ports are enabled as UARTs by default, where port 2 is
+ * a conventional RS-232 UART.
  */
 static int ftdi_stmclite_probe(struct usb_serial *serial)
 {
@@ -1865,12 +1868,13 @@ static int ftdi_stmclite_probe(struct usb_serial *serial)
 
 	dbg("%s", __func__);
 
-	if (interface == udev->actconfig->interface[2])
-		return 0;
-
+	if (interface == udev->actconfig->interface[0] ||
+	    interface == udev->actconfig->interface[1]) {
 		dev_info(&udev->dev, "Ignoring serial port reserved for JTAG\n");
-
 		return -ENODEV;
+	}
+
+	return 0;
 }
 
 /*