Re: [PATCH v2 4/6] net: ocelot: add support for ndo_change_mtu

Vladimir Oltean
2021-11-03T12:40:59Z

On Wed, Nov 03, 2021 at 10:19:41AM +0100, Clément Léger wrote:
> 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 allow for maximum
> gain of performances. Frames larger than 9000 bytes do not yield
> a noticeable improvement.
>
> 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 d76def435b23..5916492fd6d0 100644
> --- a/drivers/net/ethernet/mscc/ocelot_net.c
> +++ b/drivers/net/ethernet/mscc/ocelot_net.c
> @@ -482,6 +482,18 @@ static netdev_tx_t ocelot_port_xmit(struct sk_buff *skb, struct net_device *dev)
> return NETDEV_TX_OK;
> }
>
> +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);

The WRITE_ONCE seems absolutely gratuitous to me.

> +
> + return 0;
> +}
> +
> enum ocelot_action_type {
> OCELOT_MACT_LEARN,
> OCELOT_MACT_FORGET,
> @@ -768,6 +780,7 @@ 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;
> --
> 2.33.0
>