diff --git a/drivers/net/dsa/ocelot/felix_vsc9959.c b/drivers/net/dsa/ocelot/felix_vsc9959.c
index d9c90849274e7..3a9637496407e 100644
--- a/drivers/net/dsa/ocelot/felix_vsc9959.c
+++ b/drivers/net/dsa/ocelot/felix_vsc9959.c
@@ -1171,6 +1171,8 @@ static int vsc9959_prevalidate_phy_mode(struct ocelot *ocelot, int port,
  */
 static u16 vsc9959_wm_enc(u16 value)
 {
+	WARN_ON(value >= 16 * BIT(8));
+
 	if (value >= BIT(8))
 		return BIT(8) | (value / 16);
 
diff --git a/drivers/net/dsa/ocelot/seville_vsc9953.c b/drivers/net/dsa/ocelot/seville_vsc9953.c
index 110070a600412..9e9fd19e1d00c 100644
--- a/drivers/net/dsa/ocelot/seville_vsc9953.c
+++ b/drivers/net/dsa/ocelot/seville_vsc9953.c
@@ -911,6 +911,8 @@ static int vsc9953_prevalidate_phy_mode(struct ocelot *ocelot, int port,
  */
 static u16 vsc9953_wm_enc(u16 value)
 {
+	WARN_ON(value >= 16 * BIT(9));
+
 	if (value >= BIT(9))
 		return BIT(9) | (value / 16);
 
diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index 8518e1d60da4f..aa002db04250a 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -1253,7 +1253,7 @@ 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 pause_start, pause_stop;
-	int atop_wm;
+	int atop, atop_tot;
 
 	if (port == ocelot->npi) {
 		maxlen += OCELOT_TAG_LEN;
@@ -1274,12 +1274,12 @@ void ocelot_port_set_maxlen(struct ocelot *ocelot, int port, size_t sdu)
 	ocelot_fields_write(ocelot, port, SYS_PAUSE_CFG_PAUSE_STOP,
 			    pause_stop);
 
-	/* Tail dropping watermark */
-	atop_wm = (ocelot->shared_queue_sz - 9 * maxlen) /
+	/* Tail dropping watermarks */
+	atop_tot = (ocelot->shared_queue_sz - 9 * maxlen) /
 		   OCELOT_BUFFER_CELL_SZ;
-	ocelot_write_rix(ocelot, ocelot->ops->wm_enc(9 * maxlen),
-			 SYS_ATOP, port);
-	ocelot_write(ocelot, ocelot->ops->wm_enc(atop_wm), SYS_ATOP_TOT_CFG);
+	atop = (9 * maxlen) / OCELOT_BUFFER_CELL_SZ;
+	ocelot_write_rix(ocelot, ocelot->ops->wm_enc(atop), SYS_ATOP, port);
+	ocelot_write(ocelot, ocelot->ops->wm_enc(atop_tot), SYS_ATOP_TOT_CFG);
 }
 EXPORT_SYMBOL(ocelot_port_set_maxlen);
 
diff --git a/drivers/net/ethernet/mscc/ocelot_vsc7514.c b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
index dfb1535f26f29..8a6917691ba68 100644
--- a/drivers/net/ethernet/mscc/ocelot_vsc7514.c
+++ b/drivers/net/ethernet/mscc/ocelot_vsc7514.c
@@ -745,6 +745,8 @@ static int ocelot_reset(struct ocelot *ocelot)
  */
 static u16 ocelot_wm_enc(u16 value)
 {
+	WARN_ON(value >= 16 * BIT(8));
+
 	if (value >= BIT(8))
 		return BIT(8) | (value / 16);