diff --git a/net/can/isotp.c b/net/can/isotp.c
index a9d1357f8489..608f8c24ae46 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -109,10 +109,13 @@ MODULE_ALIAS("can-proto-6");
 /* Flow Status given in FC frame */
 #define ISOTP_FC_CTS 0		/* clear to send */
 #define ISOTP_FC_WT 1		/* wait */
 #define ISOTP_FC_OVFLW 2	/* overflow */
 
+#define ISOTP_FC_TIMEOUT 1	/* 1 sec */
+#define ISOTP_ECHO_TIMEOUT 2	/* 2 secs */
+
 enum {
 	ISOTP_IDLE = 0,
 	ISOTP_WAIT_FIRST_FC,
 	ISOTP_WAIT_FC,
 	ISOTP_WAIT_DATA,
@@ -256,11 +259,12 @@ static int isotp_send_fc(struct sock *sk, int ae, u8 flowstatus)
 
 	/* reset last CF frame rx timestamp for rx stmin enforcement */
 	so->lastrxcf_tstamp = ktime_set(0, 0);
 
 	/* start rx timeout watchdog */
-	hrtimer_start(&so->rxtimer, ktime_set(1, 0), HRTIMER_MODE_REL_SOFT);
+	hrtimer_start(&so->rxtimer, ktime_set(ISOTP_FC_TIMEOUT, 0),
+		      HRTIMER_MODE_REL_SOFT);
 	return 0;
 }
 
 static void isotp_rcv_skb(struct sk_buff *skb, struct sock *sk)
 {
@@ -342,10 +346,12 @@ static int check_pad(struct isotp_sock *so, struct canfd_frame *cf,
 				return 1;
 	}
 	return 0;
 }
 
+static void isotp_send_cframe(struct isotp_sock *so);
+
 static int isotp_rcv_fc(struct isotp_sock *so, struct canfd_frame *cf, int ae)
 {
 	struct sock *sk = &so->sk;
 
 	if (so->tx.state != ISOTP_WAIT_FC &&
@@ -396,18 +402,19 @@ static int isotp_rcv_fc(struct isotp_sock *so, struct canfd_frame *cf, int ae)
 
 	switch (cf->data[ae] & 0x0F) {
 	case ISOTP_FC_CTS:
 		so->tx.bs = 0;
 		so->tx.state = ISOTP_SENDING;
-		/* start cyclic timer for sending CF frame */
-		hrtimer_start(&so->txtimer, so->tx_gap,
+		/* send CF frame and enable echo timeout handling */
+		hrtimer_start(&so->txtimer, ktime_set(ISOTP_ECHO_TIMEOUT, 0),
 			      HRTIMER_MODE_REL_SOFT);
+		isotp_send_cframe(so);
 		break;
 
 	case ISOTP_FC_WT:
 		/* start timer to wait for next FC frame */
-		hrtimer_start(&so->txtimer, ktime_set(1, 0),
+		hrtimer_start(&so->txtimer, ktime_set(ISOTP_FC_TIMEOUT, 0),
 			      HRTIMER_MODE_REL_SOFT);
 		break;
 
 	case ISOTP_FC_OVFLW:
 		/* overflow on receiver side - report 'message too long' */
@@ -598,11 +605,11 @@ static int isotp_rcv_cf(struct sock *sk, struct canfd_frame *cf, int ae,
 	}
 
 	/* perform blocksize handling, if enabled */
 	if (!so->rxfc.bs || ++so->rx.bs < so->rxfc.bs) {
 		/* start rx timeout watchdog */
-		hrtimer_start(&so->rxtimer, ktime_set(1, 0),
+		hrtimer_start(&so->rxtimer, ktime_set(ISOTP_FC_TIMEOUT, 0),
 			      HRTIMER_MODE_REL_SOFT);
 		return 0;
 	}
 
 	/* no creation of flow control frames */
@@ -827,11 +834,11 @@ static void isotp_rcv_echo(struct sk_buff *skb, void *data)
 {
 	struct sock *sk = (struct sock *)data;
 	struct isotp_sock *so = isotp_sk(sk);
 	struct canfd_frame *cf = (struct canfd_frame *)skb->data;
 
-	/* only handle my own local echo skb's */
+	/* only handle my own local echo CF/SF skb's (no FF!) */
 	if (skb->sk != sk || so->cfecho != *(u32 *)cf->data)
 		return;
 
 	/* cancel local echo timeout */
 	hrtimer_cancel(&so->txtimer);
@@ -847,17 +854,20 @@ static void isotp_rcv_echo(struct sk_buff *skb, void *data)
 	}
 
 	if (so->txfc.bs && so->tx.bs >= so->txfc.bs) {
 		/* stop and wait for FC with timeout */
 		so->tx.state = ISOTP_WAIT_FC;
-		hrtimer_start(&so->txtimer, ktime_set(1, 0),
+		hrtimer_start(&so->txtimer, ktime_set(ISOTP_FC_TIMEOUT, 0),
 			      HRTIMER_MODE_REL_SOFT);
 		return;
 	}
 
 	/* no gap between data frames needed => use burst mode */
 	if (!so->tx_gap) {
+		/* enable echo timeout handling */
+		hrtimer_start(&so->txtimer, ktime_set(ISOTP_ECHO_TIMEOUT, 0),
+			      HRTIMER_MODE_REL_SOFT);
 		isotp_send_cframe(so);
 		return;
 	}
 
 	/* start timer to send next consecutive frame with correct delay */
@@ -877,11 +887,11 @@ static enum hrtimer_restart isotp_tx_timer_handler(struct hrtimer *hrtimer)
 		/* cfecho should be consumed by isotp_rcv_echo() here */
 		if (!so->cfecho) {
 			/* start timeout for unlikely lost echo skb */
 			hrtimer_set_expires(&so->txtimer,
 					    ktime_add(ktime_get(),
-						      ktime_set(2, 0)));
+						      ktime_set(ISOTP_ECHO_TIMEOUT, 0)));
 			restart = HRTIMER_RESTART;
 
 			/* push out the next consecutive frame */
 			isotp_send_cframe(so);
 			break;
@@ -905,11 +915,12 @@ static enum hrtimer_restart isotp_tx_timer_handler(struct hrtimer *hrtimer)
 		so->tx.state = ISOTP_IDLE;
 		wake_up_interruptible(&so->wait);
 		break;
 
 	default:
-		WARN_ON_ONCE(1);
+		WARN_ONCE(1, "can-isotp: tx timer state %08X cfecho %08X\n",
+			  so->tx.state, so->cfecho);
 	}
 
 	return restart;
 }
 
@@ -921,11 +932,11 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	struct sk_buff *skb;
 	struct net_device *dev;
 	struct canfd_frame *cf;
 	int ae = (so->opt.flags & CAN_ISOTP_EXTEND_ADDR) ? 1 : 0;
 	int wait_tx_done = (so->opt.flags & CAN_ISOTP_WAIT_TX_DONE) ? 1 : 0;
-	s64 hrtimer_sec = 0;
+	s64 hrtimer_sec = ISOTP_ECHO_TIMEOUT;
 	int off;
 	int err;
 
 	if (!so->bound)
 		return -EADDRNOTAVAIL;
@@ -940,10 +951,12 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 
 		/* wait for complete transmission of current pdu */
 		err = wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE);
 		if (err)
 			goto err_out;
+
+		so->tx.state = ISOTP_SENDING;
 	}
 
 	if (!size || size > MAX_MSG_LENGTH) {
 		err = -EINVAL;
 		goto err_out_drop;
@@ -984,10 +997,14 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	so->tx.idx = 0;
 
 	cf = (struct canfd_frame *)skb->data;
 	skb_put_zero(skb, so->ll.mtu);
 
+	/* cfecho should have been zero'ed by init / former isotp_rcv_echo() */
+	if (so->cfecho)
+		pr_notice_once("can-isotp: uninit cfecho %08X\n", so->cfecho);
+
 	/* check for single frame transmission depending on TX_DL */
 	if (size <= so->tx.ll_dl - SF_PCI_SZ4 - ae - off) {
 		/* The message size generally fits into a SingleFrame - good.
 		 *
 		 * SF_DL ESC offset optimization:
@@ -1009,15 +1026,12 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 		if (off)
 			cf->data[SF_PCI_SZ4 + ae] = size;
 		else
 			cf->data[ae] |= size;
 
-		so->tx.state = ISOTP_IDLE;
-		wake_up_interruptible(&so->wait);
-
-		/* don't enable wait queue for a single frame transmission */
-		wait_tx_done = 0;
+		/* set CF echo tag for isotp_rcv_echo() (SF-mode) */
+		so->cfecho = *(u32 *)cf->data;
 	} else {
 		/* send first frame */
 
 		isotp_create_fframe(cf, so, ae);
 
@@ -1029,35 +1043,27 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 				so->tx_gap = ktime_set(0, so->frame_txtime);
 
 			/* disable wait for FCs due to activated block size */
 			so->txfc.bs = 0;
 
-			/* cfecho should have been zero'ed by init */
-			if (so->cfecho)
-				pr_notice_once("can-isotp: no fc cfecho %08X\n",
-					       so->cfecho);
-
-			/* set consecutive frame echo tag */
+			/* set CF echo tag for isotp_rcv_echo() (CF-mode) */
 			so->cfecho = *(u32 *)cf->data;
-
-			/* switch directly to ISOTP_SENDING state */
-			so->tx.state = ISOTP_SENDING;
-
-			/* start timeout for unlikely lost echo skb */
-			hrtimer_sec = 2;
 		} else {
 			/* standard flow control check */
 			so->tx.state = ISOTP_WAIT_FIRST_FC;
 
 			/* start timeout for FC */
-			hrtimer_sec = 1;
-		}
+			hrtimer_sec = ISOTP_FC_TIMEOUT;
 
-		hrtimer_start(&so->txtimer, ktime_set(hrtimer_sec, 0),
-			      HRTIMER_MODE_REL_SOFT);
+			/* no CF echo tag for isotp_rcv_echo() (FF-mode) */
+			so->cfecho = 0;
+		}
 	}
 
+	hrtimer_start(&so->txtimer, ktime_set(hrtimer_sec, 0),
+		      HRTIMER_MODE_REL_SOFT);
+
 	/* send the first or only CAN frame */
 	cf->flags = so->ll.tx_flags;
 
 	skb->dev = dev;
 	skb->sk = sk;
@@ -1066,12 +1072,11 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	if (err) {
 		pr_notice_once("can-isotp: %s: can_send_ret %pe\n",
 			       __func__, ERR_PTR(err));
 
 		/* no transmission -> no timeout monitoring */
-		if (hrtimer_sec)
-			hrtimer_cancel(&so->txtimer);
+		hrtimer_cancel(&so->txtimer);
 
 		/* reset consecutive frame echo tag */
 		so->cfecho = 0;
 
 		goto err_out_drop;
