diff --git a/sllin/sllin.c b/sllin/sllin.c
index 2db896f..2969448 100644
--- a/sllin/sllin.c
+++ b/sllin/sllin.c
@@ -869,7 +869,6 @@ static int sllin_send_tx_buff(struct sllin *sl)
 #else
 		remains = sl->tx_lim - sl->tx_cnt;
 #endif
-
 		res = tty->ops->write(tty, sl->tx_buff + sl->tx_cnt, remains);
 		if (res < 0)
 			goto error_in_write;
@@ -916,10 +915,25 @@ static int sllin_send_break(struct sllin *sl)
 	unsigned long break_baud;
 	int res;
 
+	netdev_dbg(sl->dev, "%s()#<BREAK_BY_BAUD>  invoke.\n", __func__);
+	if (tty == NULL) {
+		netdev_dbg(sl->dev, "%s() tty == NULL.\n", __func__);
+		sl->lin_state = SLSTATE_IDLE;
+		return -1;
+	}
+	if (tty->ops == NULL) {
+		netdev_dbg(sl->dev, "%s() tty->ops == NULL.\n", __func__);
+		sl->lin_state = SLSTATE_IDLE;
+		return -1;
+	}
 	break_baud = ((sl->lin_baud * 2) / 3);
 	sltty_change_speed(tty, break_baud);
 
-	tty->ops->flush_buffer(tty);
+	if (tty->ops->flush_buffer) {
+		tty->ops->flush_buffer(tty);
+	} else {
+		netdev_dbg(sl->dev, "%s() tty->ops->flush_buffer is NULL.\n", __func__);
+	}
 	sl->rx_cnt = SLLIN_BUFF_BREAK;
 
 	sl->rx_expect = SLLIN_BUFF_BREAK + 1;
@@ -943,6 +957,17 @@ static int sllin_send_break(struct sllin *sl)
 	unsigned long usleep_range_min;
 	unsigned long usleep_range_max;
 
+	netdev_dbg(sl->dev, "%s() invoke.\n", __func__);
+	if (tty == NULL) {
+		netdev_dbg(sl->dev, "%s() tty == NULL.\n", __func__);
+		sl->lin_state = SLSTATE_IDLE;
+		return -1;
+	}
+	if (tty->ops == NULL) {
+		netdev_dbg(sl->dev, "%s() tty->ops == NULL.\n", __func__);
+		sl->lin_state = SLSTATE_IDLE;
+		return -1;
+	}
 	break_baud = ((sl->lin_baud * 2) / 3);
 	sl->rx_cnt = SLLIN_BUFF_BREAK;
 	sl->rx_expect = SLLIN_BUFF_BREAK + 1;
@@ -950,21 +975,31 @@ static int sllin_send_break(struct sllin *sl)
 
 	/* Do the break ourselves; Inspired by
 	   http://lxr.linux.no/#linux+v3.1.2/drivers/tty/tty_io.c#L2452 */
-	retval = tty->ops->break_ctl(tty, -1);
-	if (retval)
-		return retval;
+	if (tty->ops->break_ctl) {
+		retval = tty->ops->break_ctl(tty, -1);
+		if (retval)
+			return retval;
+	} else {
+		netdev_dbg(sl->dev, "%s() tty->ops->break_ctl is NULL.\n", __func__);
+	}
 
 	/* udelay(712); */
 	usleep_range_min = (1000000l * SLLIN_SAMPLES_PER_CHAR) / break_baud;
 	usleep_range_max = usleep_range_min + 50;
 	usleep_range(usleep_range_min, usleep_range_max);
 
-	retval = tty->ops->break_ctl(tty, 0);
+	if(tty->ops->break_ctl) {
+		retval = tty->ops->break_ctl(tty, 0);
+	} 
 	usleep_range_min = (1000000l * 1 /* 1 bit */) / break_baud;
 	usleep_range_max = usleep_range_min + 30;
 	usleep_range(usleep_range_min, usleep_range_max);
 
-	tty->ops->flush_buffer(tty);
+	if ( tty->ops->flush_buffer) {
+		tty->ops->flush_buffer(tty);
+	} else {
+		netdev_dbg(sl->dev, "%s() tty->ops->flush_buffer is NULL.\n", __func__);
+	}
 
 	sl->tx_cnt = SLLIN_BUFF_SYNC;
 
@@ -1028,6 +1063,12 @@ static int sllin_kwthread(void *ptr)
 		int lin_dlc;
 		u8 lin_data_buff[SLLIN_DATA_MAX];
 
+		if (sl == NULL) {
+			pr_err("sllin: sl is NULL\n");
+		}
+		if (sl->dev == NULL) {
+			pr_err("sllin: sl->dev is NULL\n");
+		}
 
 		if ((sl->lin_state == SLSTATE_IDLE) && sl->lin_master &&
 			sl->id_to_send) {
@@ -1036,6 +1077,7 @@ static int sllin_kwthread(void *ptr)
 			}
 		}
 
+		netdev_dbg(sl->dev, "sllin_kthread <WAIT_EVENT>\n");
 		wait_event_killable(sl->kwt_wq, kthread_should_stop() ||
 			test_bit(SLF_RXEVENT, &sl->flags) ||
 			test_bit(SLF_TXEVENT, &sl->flags) ||
@@ -1046,6 +1088,7 @@ static int sllin_kwthread(void *ptr)
 				(sl->lin_state == SLSTATE_RESPONSE_WAIT))
 				&& test_bit(SLF_MSGEVENT, &sl->flags)));
 
+		netdev_dbg(sl->dev, "sllin_kthread <WAKEUPED>\n");
 		if (test_and_clear_bit(SLF_RXEVENT, &sl->flags)) {
 			netdev_dbg(sl->dev, "sllin_kthread RXEVENT\n");
 		}
@@ -1078,21 +1121,25 @@ static int sllin_kwthread(void *ptr)
 			sl->lin_state = SLSTATE_IDLE;
 		}
 
+		netdev_dbg(sl->dev, "sllin_kthread: lin_state <%08x>\n",sl->lin_state);
 		switch (sl->lin_state) {
 		case SLSTATE_IDLE:
 			if (!test_bit(SLF_MSGEVENT, &sl->flags))
 				break;
-
+			if (sl->tx_req_skb == NULL)
+				netdev_dbg(sl->dev, "sl->tx_req_skb == NULL\n");
+			if (sl->tx_req_skb->data == NULL)
+				netdev_dbg(sl->dev, "sl->tx_req_skb->data == NULL\n");
 			cf = (struct can_frame *)sl->tx_req_skb->data;
 
 			/* SFF RTR CAN frame -> LIN header */
 			if (cf->can_id & CAN_RTR_FLAG) {
 				struct sllin_conf_entry *sce;
 
-				netdev_dbg(sl->dev, "%s: RTR SFF CAN frame, ID = %x\n",
-					__func__, cf->can_id & LIN_ID_MASK);
 
 				sce = &sl->linfr_cache[cf->can_id & LIN_ID_MASK];
+				netdev_dbg(sl->dev, "%s: RTR SFF CAN frame, ID = %x dlc=%d\n",
+					__func__, cf->can_id & LIN_ID_MASK, sce->dlc);
 				spin_lock_irqsave(&sl->linfr_lock, flags);
 
 				/* Is there Slave response in linfr_cache to be sent? */
@@ -1114,8 +1161,8 @@ static int sllin_kwthread(void *ptr)
 				spin_unlock_irqrestore(&sl->linfr_lock, flags);
 
 			} else { /* SFF NON-RTR CAN frame -> LIN header + LIN response */
-				netdev_dbg(sl->dev, "%s: NON-RTR SFF CAN frame, ID = %x\n",
-					__func__, (int)cf->can_id & LIN_ID_MASK);
+				netdev_dbg(sl->dev, "%s: NON-RTR SFF CAN frame, ID = %x\n dlc=%d",
+					__func__, (int)cf->can_id & LIN_ID_MASK, cf->can_dlc);
 
 				lin_data = cf->data;
 				lin_dlc = cf->can_dlc;
@@ -1140,6 +1187,7 @@ static int sllin_kwthread(void *ptr)
 			hrtimer_start(&sl->rx_timer,
 				ktime_add(ktime_get(), sl->rx_timer_timeout),
 				HRTIMER_MODE_ABS);
+			netdev_dbg(sl->dev, "sllin_kthread: SLSTATE finish\n");
 			break;
 
 		case SLSTATE_BREAK_SENT:
@@ -1654,3 +1702,4 @@ static void __exit sllin_exit(void)
 
 module_init(sllin_init);
 module_exit(sllin_exit);
+