[1/1] tty: n_gsm: make n_gsm line number configurable

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 5e516f5cac5a..fafef4edea4f 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -228,7 +228,7 @@  struct gsm_mux {
 	struct tty_struct *tty;		/* The tty our ldisc is bound to */
 	spinlock_t lock;
 	struct mutex mutex;
-	unsigned int num;
+	unsigned short num;
 	struct kref ref;
 
 	/* Events on the GSM channel */
@@ -519,6 +519,64 @@  static void gsm_hex_dump_bytes(const char *fname, const u8 *data,
 	kfree(prefix);
 }
 
+/**
+ * gsm_get_mux	-	find a mux instance by line number
+ *
+ * @num:    the mux line number to search for may differ from the position
+ *          in the mux array.
+ *
+ * @return: Pointer of the mux instance with index <index> or
+ *          NULL if no instance with that index exists
+ */
+static struct gsm_mux *gsm_get_mux(unsigned int num)
+{
+	unsigned int i;
+	struct gsm_mux *gsm;
+
+	/* find the object with that line number */
+	spin_lock(&gsm_mux_lock);
+	for (i = 0, gsm = NULL; i < MAX_MUX; i++) {
+		if (gsm_mux[i]) {
+			if (num == gsm_mux[i]->num) {
+				gsm = gsm_mux[i];
+				break;
+			}
+		}
+	}
+	spin_unlock(&gsm_mux_lock);
+	return gsm;
+}
+
+/**
+ * gsm_assign_num	-	assigns a new mux line number
+ *
+ * @gsm: GSM mux
+ * @num: the desired new mux line number
+ *
+ * The global GSM mux line table is modified to reflect this change.
+ */
+static int gsm_assign_num(struct gsm_mux *gsm, unsigned int num)
+{
+	int ret = 0;
+
+	if (gsm->num >= MAX_MUX || num >= MAX_MUX)
+		return -EINVAL;
+
+	spin_lock(&gsm_mux_lock);
+	if (!gsm_mux[num]) {
+		if (gsm_mux[gsm->num])
+			gsm_mux[gsm->num] = NULL;
+		gsm_mux[num] = gsm;
+		gsm->num = num;
+	} else if (gsm->num != num) {
+		/* Setting an occupied line number is not allowed. */
+		ret = -EBUSY;
+	}
+	spin_unlock(&gsm_mux_lock);
+
+	return ret;
+}
+
 /**
  *	gsm_register_devices	-	register all tty devices for a given mux index
  *
@@ -2700,6 +2758,8 @@  static void gsm_copy_config_values(struct gsm_mux *gsm,
 	c->mru = gsm->mru;
 	c->mtu = gsm->mtu;
 	c->k = 0;
+	c->numValid = 1;
+	c->num = gsm->num;
 }
 
 static int gsm_config(struct gsm_mux *gsm, struct gsm_config *c)
@@ -2707,6 +2767,7 @@  static int gsm_config(struct gsm_mux *gsm, struct gsm_config *c)
 	int ret = 0;
 	int need_close = 0;
 	int need_restart = 0;
+	struct gsm_mux *found;
 
 	/* Stuff we don't support yet - UI or I frame transport, windowing */
 	if ((c->adaption != 1 && c->adaption != 2) || c->k)
@@ -2722,10 +2783,22 @@  static int gsm_config(struct gsm_mux *gsm, struct gsm_config *c)
 		return -EINVAL;
 	if (c->i == 0 || c->i > 2)	/* UIH and UI only */
 		return -EINVAL;
+	if (c->numValid) {
+		if (c->num >= MAX_MUX)
+			return -EINVAL;
+		found = gsm_get_mux(c->num);
+		if (found) {
+			/* If there is a mux with that number then it must be the same. */
+			if (found != gsm)
+				return -EBUSY;
+		}
+	}
 	/*
 	 * See what is needed for reconfiguration
 	 */
-
+	/* Line number */
+	if (c->numValid && gsm->num != c->num)
+		need_restart = true;
 	/* Timing fields */
 	if (c->t1 != 0 && c->t1 != gsm->t1)
 		need_restart = 1;
@@ -2748,8 +2821,14 @@  static int gsm_config(struct gsm_mux *gsm, struct gsm_config *c)
 	 * configuration. On the first time there is no DLCI[0]
 	 * and closing or cleaning up is not necessary.
 	 */
-	if (need_close || need_restart)
+	if (need_close || need_restart) {
 		gsm_cleanup_mux(gsm, true);
+		if (c->numValid) {
+			ret = gsm_assign_num(gsm, c->num);
+			if (ret)
+				return ret;
+		}
+	}
 
 	gsm->initiator = c->initiator;
 	gsm->mru = c->mru;
diff --git a/include/uapi/linux/gsmmux.h b/include/uapi/linux/gsmmux.h
index cb8693b39cb7..03b28a0076d8 100644
--- a/include/uapi/linux/gsmmux.h
+++ b/include/uapi/linux/gsmmux.h
@@ -19,7 +19,9 @@  struct gsm_config
 	unsigned int mtu;
 	unsigned int k;
 	unsigned int i;
-	unsigned int unused[8];		/* Padding for expansion without
+	unsigned short numValid;
+	unsigned short num;
+	unsigned int unused[7];		/* Padding for expansion without
 					   breaking stuff */
 };