[PATCH net-next v4 3/4] net: ocelot: add support for ndo_change_mtu

["Clément Léger" <clement.leger@bootlin.com>]

This commit adds support for changing MTU for the ocelot register based
interface. For ocelot, JUMBO frame size can be set up to 25000 bytes
but has been set to 9000 which is a saner value and allows for maximum
gain of performance with FDMA.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
---
 drivers/net/ethernet/mscc/ocelot.h     |  2 ++
 drivers/net/ethernet/mscc/ocelot_net.c | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/drivers/net/ethernet/mscc/ocelot.h b/drivers/net/ethernet/mscc/ocelot.h
index e43da09b8f91..ba0dec7dd64f 100644
--- a/drivers/net/ethernet/mscc/ocelot.h
+++ b/drivers/net/ethernet/mscc/ocelot.h
@@ -32,6 +32,8 @@
 
 #define OCELOT_PTP_QUEUE_SZ	128
 
+#define OCELOT_JUMBO_MTU	9000
+
 struct ocelot_port_tc {
 	bool block_shared;
 	unsigned long offload_cnt;
diff --git a/drivers/net/ethernet/mscc/ocelot_net.c b/drivers/net/ethernet/mscc/ocelot_net.c
index b589ae95e29b..459e81c46da2 100644
--- a/drivers/net/ethernet/mscc/ocelot_net.c
+++ b/drivers/net/ethernet/mscc/ocelot_net.c
@@ -764,10 +764,23 @@ static int ocelot_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 	return phy_mii_ioctl(dev->phydev, ifr, cmd);
 }
 
+static int ocelot_change_mtu(struct net_device *dev, int new_mtu)
+{
+	struct ocelot_port_private *priv = netdev_priv(dev);
+	struct ocelot_port *ocelot_port = &priv->port;
+	struct ocelot *ocelot = ocelot_port->ocelot;
+
+	ocelot_port_set_maxlen(ocelot, priv->chip_port, new_mtu);
+	WRITE_ONCE(dev->mtu, new_mtu);
+
+	return 0;
+}
+
 static const struct net_device_ops ocelot_port_netdev_ops = {
 	.ndo_open			= ocelot_port_open,
 	.ndo_stop			= ocelot_port_stop,
 	.ndo_start_xmit			= ocelot_port_xmit,
+	.ndo_change_mtu			= ocelot_change_mtu,
 	.ndo_set_rx_mode		= ocelot_set_rx_mode,
 	.ndo_set_mac_address		= ocelot_port_set_mac_address,
 	.ndo_get_stats64		= ocelot_get_stats64,
@@ -1699,6 +1712,7 @@ int ocelot_probe_port(struct ocelot *ocelot, int port, struct regmap *target,
 
 	dev->netdev_ops = &ocelot_port_netdev_ops;
 	dev->ethtool_ops = &ocelot_ethtool_ops;
+	dev->max_mtu = OCELOT_JUMBO_MTU;
 
 	dev->hw_features |= NETIF_F_HW_VLAN_CTAG_FILTER | NETIF_F_RXFCS |
 		NETIF_F_HW_TC;
-- 
2.34.1