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>

1 files changed, 18 insertions, 5 deletions

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 09e8c7d53af3..7290394e3131 100644
--- a/drivers/tty/n_gsm.c
+++ b/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: