linux-kernel - Re: [PATCH v2 4/6] net: ocelot: add support for ndo_change

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Date:   Wed, 3 Nov 2021 12:40:55 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Clément Léger <clement.leger@...tlin.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 4/6] net: ocelot: add support for ndo_change_mtu

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@...tlin.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
>