diff --git a/drivers/net/dsa/ocelot/felix.c b/drivers/net/dsa/ocelot/felix.c
index 9f9efb974003..eef9fa812a3c 100644
--- a/drivers/net/dsa/ocelot/felix.c
+++ b/drivers/net/dsa/ocelot/felix.c
@@ -533,6 +533,7 @@ static int felix_setup(struct dsa_switch *ds)
 			 ANA_PGID_PGID_PGID(GENMASK(ocelot->num_phys_ports, 0)),
 			 ANA_PGID_PGID, PGID_UC);
 
+	ds->mtu_enforcement_ingress = true;
 	/* It looks like the MAC/PCS interrupt register - PM0_IEVENT (0x8040)
 	 * isn't instantiated for the Felix PF.
 	 * In-band AN may take a few ms to complete, so we need to poll.
@@ -610,6 +611,22 @@ static bool felix_txtstamp(struct dsa_switch *ds, int port,
 	return false;
 }
 
+static int felix_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
+{
+	struct ocelot *ocelot = ds->priv;
+
+	ocelot_port_set_maxlen(ocelot, port, new_mtu);
+
+	return 0;
+}
+
+static int felix_get_max_mtu(struct dsa_switch *ds, int port)
+{
+	struct ocelot *ocelot = ds->priv;
+
+	return ocelot_get_max_mtu(ocelot, port);
+}
+
 static int felix_cls_flower_add(struct dsa_switch *ds, int port,
 				struct flow_cls_offload *cls, bool ingress)
 {
@@ -665,6 +682,8 @@ static const struct dsa_switch_ops felix_switch_ops = {
 	.port_hwtstamp_set	= felix_hwtstamp_set,
 	.port_rxtstamp		= felix_rxtstamp,
 	.port_txtstamp		= felix_txtstamp,
+	.port_change_mtu	= felix_change_mtu,
+	.port_max_mtu		= felix_get_max_mtu,
 	.cls_flower_add		= felix_cls_flower_add,
 	.cls_flower_del		= felix_cls_flower_del,
 	.cls_flower_stats	= felix_cls_flower_stats,
diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index 114d6053aa26..b5f925c1b5b2 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -1998,13 +1998,25 @@ EXPORT_SYMBOL(ocelot_switchdev_blocking_nb);
 
 /* Configure the maximum SDU (L2 payload) on RX to the value specified in @sdu.
  * The length of VLAN tags is accounted for automatically via DEV_MAC_TAGS_CFG.
+ * In the special case that it's the NPI port that we're configuring, the
+ * length of the tag and optional prefix needs to be accounted for privately,
+ * in order to be able to sustain communication at the requested @sdu.
  */
-static void ocelot_port_set_maxlen(struct ocelot *ocelot, int port, size_t sdu)
+void ocelot_port_set_maxlen(struct ocelot *ocelot, int port, size_t sdu)
 {
 	struct ocelot_port *ocelot_port = ocelot->ports[port];
 	int maxlen = sdu + ETH_HLEN + ETH_FCS_LEN;
 	int atop_wm;
 
+	if (port == ocelot->npi) {
+		maxlen += OCELOT_TAG_LEN;
+
+		if (ocelot->inj_prefix == OCELOT_TAG_PREFIX_SHORT)
+			maxlen += OCELOT_SHORT_PREFIX_LEN;
+		else if (ocelot->inj_prefix == OCELOT_TAG_PREFIX_LONG)
+			maxlen += OCELOT_LONG_PREFIX_LEN;
+	}
+
 	ocelot_port_writel(ocelot_port, maxlen, DEV_MAC_MAXLEN_CFG);
 
 	/* Set Pause WM hysteresis
@@ -2022,6 +2034,24 @@ static void ocelot_port_set_maxlen(struct ocelot *ocelot, int port, size_t sdu)
 			 SYS_ATOP, port);
 	ocelot_write(ocelot, ocelot_wm_enc(atop_wm), SYS_ATOP_TOT_CFG);
 }
+EXPORT_SYMBOL(ocelot_port_set_maxlen);
+
+int ocelot_get_max_mtu(struct ocelot *ocelot, int port)
+{
+	int max_mtu = 65535 - ETH_HLEN - ETH_FCS_LEN;
+
+	if (port == ocelot->npi) {
+		max_mtu -= OCELOT_TAG_LEN;
+
+		if (ocelot->inj_prefix == OCELOT_TAG_PREFIX_SHORT)
+			max_mtu -= OCELOT_SHORT_PREFIX_LEN;
+		else if (ocelot->inj_prefix == OCELOT_TAG_PREFIX_LONG)
+			max_mtu -= OCELOT_LONG_PREFIX_LEN;
+	}
+
+	return max_mtu;
+}
+EXPORT_SYMBOL(ocelot_get_max_mtu);
 
 void ocelot_init_port(struct ocelot *ocelot, int port)
 {
@@ -2131,6 +2161,10 @@ void ocelot_configure_cpu(struct ocelot *ocelot, int npi,
 {
 	int cpu = ocelot->num_phys_ports;
 
+	ocelot->npi = npi;
+	ocelot->inj_prefix = injection;
+	ocelot->xtr_prefix = extraction;
+
 	/* The unicast destination PGID for the CPU port module is unused */
 	ocelot_write_rix(ocelot, 0, ANA_PGID_PGID, cpu);
 	/* Instead set up a multicast destination PGID for traffic copied to
@@ -2143,19 +2177,10 @@ void ocelot_configure_cpu(struct ocelot *ocelot, int npi,
 			 ANA_PORT_PORT_CFG, cpu);
 
 	if (npi >= 0 && npi < ocelot->num_phys_ports) {
-		int sdu = ETH_DATA_LEN + OCELOT_TAG_LEN;
-
 		ocelot_write(ocelot, QSYS_EXT_CPU_CFG_EXT_CPUQ_MSK_M |
 			     QSYS_EXT_CPU_CFG_EXT_CPU_PORT(npi),
 			     QSYS_EXT_CPU_CFG);
 
-		if (injection == OCELOT_TAG_PREFIX_SHORT)
-			sdu += OCELOT_SHORT_PREFIX_LEN;
-		else if (injection == OCELOT_TAG_PREFIX_LONG)
-			sdu += OCELOT_LONG_PREFIX_LEN;
-
-		ocelot_port_set_maxlen(ocelot, npi, sdu);
-
 		/* Enable NPI port */
 		ocelot_write_rix(ocelot,
 				 QSYS_SWITCH_PORT_MODE_INGRESS_DROP_MODE |
diff --git a/include/soc/mscc/ocelot.h b/include/soc/mscc/ocelot.h
index db2fb14bd775..23a78d927838 100644
--- a/include/soc/mscc/ocelot.h
+++ b/include/soc/mscc/ocelot.h
@@ -522,6 +522,11 @@ struct ocelot {
 	 */
 	u8				num_phys_ports;
 
+	int				npi;
+
+	enum ocelot_tag_prefix		inj_prefix;
+	enum ocelot_tag_prefix		xtr_prefix;
+
 	u32				*lags;
 
 	struct list_head		multicast;
@@ -616,6 +621,8 @@ int ocelot_hwstamp_set(struct ocelot *ocelot, int port, struct ifreq *ifr);
 int ocelot_port_add_txtstamp_skb(struct ocelot_port *ocelot_port,
 				 struct sk_buff *skb);
 void ocelot_get_txtstamp(struct ocelot *ocelot);
+void ocelot_port_set_maxlen(struct ocelot *ocelot, int port, size_t sdu);
+int ocelot_get_max_mtu(struct ocelot *ocelot, int port);
 int ocelot_cls_flower_replace(struct ocelot *ocelot, int port,
 			      struct flow_cls_offload *f, bool ingress);
 int ocelot_cls_flower_destroy(struct ocelot *ocelot, int port,
