USB: qcserial: Enable Diagnostics Monitor and GPS ports on Gobi 2000

this patch to qcserial.c enables the Diagnostics Monitor
and NMEA GPS ports on Qualcomm Gobi 2000 devices.

A Gobi 2000 device will provide 3 serial ports:
# /dev/ttyUSB0 -> Diagnostics
# /dev/ttyUSB1 -> 3G Modem
# /dev/ttyUSB2 -> NMEA GPS port

* The Diagnostics Monitor uses Qualcomm's DM protocol; I used
libqcdm (ModemManager) to talk to it, found it working, but at
least DM commands 12 and 64 are not implemented on my device
(Gobi 2000 built into Thinkpad x100e).

* Functionality of the 3G Modem port remains unchanged.

* The GPS port and how to enable it has been confirmed now in the
Gobi 3000 source code at:
https://www.codeaurora.org/patches/quic/gobi/
Enable/disable GPS via:
echo "\$GPS_START" > /dev/ttyUSB2
# use GPS
echo "\$GPS_STOP" > /dev/ttyUSB2


Signed-off-by: Matthias G. Eckermann <[e-mail]>

drivers/usb/serial/qcserial.c

···
 	case 3:
 	case 4:
 		/* Composite mode */
-		if (ifnum == 2) {
+		/* ifnum == 0 is a broadband network adapter */
+		if (ifnum == 1) {
+			/*
+			 * Diagnostics Monitor (serial line 9600 8N1)
+			 * Qualcomm DM protocol
+			 * use "libqcdm" (ModemManager) for communication
+			 */
+			dbg("Diagnostics Monitor found");
+			retval = usb_set_interface(serial->dev, ifnum, 0);
+			if (retval < 0) {
+				dev_err(&serial->dev->dev,
+					"Could not set interface, error %d\n",
+					retval);
+				retval = -ENODEV;
+			}
+		} else if (ifnum == 2) {
 			dbg("Modem port found");
 			retval = usb_set_interface(serial->dev, ifnum, 0);
 			if (retval < 0) {
···
 				kfree(data);
 			}
 			return retval;
+		} else if (ifnum==3) {
+			/*
+			 * NMEA (serial line 9600 8N1)
+			 * # echo "\$GPS_START" > /dev/ttyUSBx
+			 * # echo "\$GPS_STOP"  > /dev/ttyUSBx
+			 */
+			dbg("NMEA GPS interface found");
+			retval = usb_set_interface(serial->dev, ifnum, 0);
+			if (retval < 0) {
+				dev_err(&serial->dev->dev,
+					"Could not set interface, error %d\n",
+					retval);
+				retval = -ENODEV;
+			}
 		}
 		break;