[PATCH net-next v2 1/2] dsa: lan9303: Add port_max_mtu API

[Jerry Ray <jerry.ray@microchip.com>]

Adding in support for reporting the max mtu for a given
port.

Signed-off-by: Jerry Ray <jerry.ray@microchip.com>
---
 drivers/net/dsa/lan9303-core.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/net/dsa/lan9303-core.c b/drivers/net/dsa/lan9303-core.c
index 80f07bd20593..baa336bb9d15 100644
--- a/drivers/net/dsa/lan9303-core.c
+++ b/drivers/net/dsa/lan9303-core.c
@@ -1279,6 +1279,25 @@ static int lan9303_port_mdb_del(struct dsa_switch *ds, int port,
 	return 0;
 }
 
+/* For non-cpu ports, the max frame size is 1518.
+ * The CPU port supports a max frame size of 1522.
+ * There is a JUMBO flag to make the max size 2048, but this driver
+ * presently does not support using it.
+ */
+static int lan9303_port_max_mtu(struct dsa_switch *ds, int port)
+{
+	struct net_device *p = dsa_port_to_master(dsa_to_port(ds, port));
+	struct lan9303 *chip = ds->priv;
+
+	dev_dbg(chip->dev, "%s(%d) entered. NET max_mtu is %d",
+		__func__, port, p->max_mtu);
+
+	if (dsa_port_is_cpu(dsa_to_port(ds, port)))
+		return 1522 - ETH_HLEN - ETH_FCS_LEN;
+	else
+		return 1518 - ETH_HLEN - ETH_FCS_LEN;
+}
+
 static const struct dsa_switch_ops lan9303_switch_ops = {
 	.get_tag_protocol = lan9303_get_tag_protocol,
 	.setup = lan9303_setup,
@@ -1299,6 +1318,7 @@ static const struct dsa_switch_ops lan9303_switch_ops = {
 	.port_fdb_dump          = lan9303_port_fdb_dump,
 	.port_mdb_add           = lan9303_port_mdb_add,
 	.port_mdb_del           = lan9303_port_mdb_del,
+	.port_max_mtu		= lan9303_port_max_mtu,
 };
 
 static int lan9303_register_switch(struct lan9303 *chip)
-- 
2.17.1