qcserial: bind to DM/DIAG port on Gobi 1K devices

commit 3f8bc5e4 upstream.

Turns out we just need altsetting 1 and then we can talk to it.
Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/qcserial.c

@@ -197,12 +197,15 @@ static int qcprobe(struct usb_serial *serial, const struct usb_device_id *id)
 
 	if (is_gobi1k) {
 		/* Gobi 1K USB layout:
-		 * 0: serial port (doesn't respond)
+		 * 0: DM/DIAG (use libqcdm from ModemManager for communication)
 		 * 1: serial port (doesn't respond)
 		 * 2: AT-capable modem port
 		 * 3: QMI/net
 		 */
-		if (ifnum == 2)
+		if (ifnum == 0) {
+			dev_dbg(dev, "Gobi 1K DM/DIAG interface found\n");
+			altsetting = 1;
+		} else if (ifnum == 2)
 			dev_dbg(dev, "Modem port found\n");
 		else
 			altsetting = -1;