tty: n_gsm: Fixed logic to decode break signal from modem status

The modem status can be one or 2 octets and contains the V.24 signals
and in the 2 octet case also the break signal.
We were improperly decoding the break signal from the modem in the
2 octet case.
Signed-off-by: Russ Gorby <russ.gorby@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/tty/n_gsm.c

@@ -984,10 +984,22 @@ static void gsm_control_reply(struct gsm_mux *gsm, int cmd, u8 *data,
  */
 
 static void gsm_process_modem(struct tty_struct *tty, struct gsm_dlci *dlci,
-							u32 modem)
+							u32 modem, int clen)
 {
 	int  mlines = 0;
-	u8 brk = modem >> 6;
+	u8 brk = 0;
+
+	/* The modem status command can either contain one octet (v.24 signals)
+	   or two octets (v.24 signals + break signals). The length field will
+	   either be 2 or 3 respectively. This is specified in section
+	   5.4.6.3.7 of the  27.010 mux spec. */
+
+	if (clen == 2)
+		modem = modem & 0x7f;
+	else {
+		brk = modem & 0x7f;
+		modem = (modem >> 7) & 0x7f;
+	};
 
 	/* Flow control/ready to communicate */
 	if (modem & MDM_FC) {
@@ -1061,7 +1073,7 @@ static void gsm_control_modem(struct gsm_mux *gsm, u8 *data, int clen)
 			return;
 	}
 	tty = tty_port_tty_get(&dlci->port);
-	gsm_process_modem(tty, dlci, modem);
+	gsm_process_modem(tty, dlci, modem, clen);
 	if (tty) {
 		tty_wakeup(tty);
 		tty_kref_put(tty);
@@ -1482,12 +1494,13 @@ static void gsm_dlci_begin_close(struct gsm_dlci *dlci)
  *	open we shovel the bits down it, if not we drop them.
  */
 
-static void gsm_dlci_data(struct gsm_dlci *dlci, u8 *data, int len)
+static void gsm_dlci_data(struct gsm_dlci *dlci, u8 *data, int clen)
 {
 	/* krefs .. */
 	struct tty_port *port = &dlci->port;
 	struct tty_struct *tty = tty_port_tty_get(port);
 	unsigned int modem = 0;
+	int len = clen;
 
 	if (debug & 16)
 		pr_debug("%d bytes for tty %p\n", len, tty);
@@ -1507,7 +1520,7 @@ static void gsm_dlci_data(struct gsm_dlci *dlci, u8 *data, int len)
 				if (len == 0)
 					return;
 			}
-			gsm_process_modem(tty, dlci, modem);
+			gsm_process_modem(tty, dlci, modem, clen);
 		/* Line state will go via DLCI 0 controls only */
 		case 1:
 		default: