net: mscc: ocelot: warn when encoding an out-of-bounds watermark value

There is an upper bound to the value that a watermark may hold. That
upper bound is not immediately obvious during configuration, and it
might be possible to have accidental truncation.

Actually this has happened already, add a warning to prevent it from
happening again.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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);
 

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);
 

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);