netdev - Re: [PATCH 3/4] net: dsa: realtek: rtl8365mb: Add setting MTU

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Message-ID: <20220510164913.trpkw6yt7rdxqht4@bang-olufsen.dk>
Date:   Tue, 10 May 2022 16:49:14 +0000
From:   Alvin Šipraga <ALSI@...g-olufsen.dk>
To:     Hauke Mehrtens <hauke@...ke-m.de>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "olteanv@...il.com" <olteanv@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 3/4] net: dsa: realtek: rtl8365mb: Add setting MTU

On Mon, May 09, 2022 at 12:48:47AM +0200, Hauke Mehrtens wrote:
> The switch does not support per port MTU setting, but only a MRU
> setting. Implement this by setting the MTU on the CPU port.
> 
> Without this patch the MRU was always set to 1536, not it is set by the

s/not/now/

> DSA subsystem and the user scan change it.
> 
> Signed-off-by: Hauke Mehrtens <hauke@...ke-m.de>
> ---
>  drivers/net/dsa/realtek/rtl8365mb.c | 43 ++++++++++++++++++++++++-----
>  1 file changed, 36 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/realtek/rtl8365mb.c
> index be64cfdeccc7..f9b690251155 100644
> --- a/drivers/net/dsa/realtek/rtl8365mb.c
> +++ b/drivers/net/dsa/realtek/rtl8365mb.c
> @@ -1132,6 +1132,38 @@ static int rtl8365mb_port_set_isolation(struct realtek_priv *priv, int port,
>  	return regmap_write(priv->map, RTL8365MB_PORT_ISOLATION_REG(port), mask);
>  }
>  
> +static int rtl8365mb_port_change_mtu(struct dsa_switch *ds, int port,
> +				     int new_mtu)
> +{
> +	struct dsa_port *dp = dsa_to_port(ds, port);
> +	struct realtek_priv *priv = ds->priv;
> +	int length;
> +
> +	/* When a new MTU is set, DSA always set the CPU port's MTU to the

s/set/sets/

> +	 * largest MTU of the slave ports. Because the switch only has a global
> +	 * RX length register, only allowing CPU port here is enough.
> +	 */
> +	if (!dsa_is_cpu_port(ds, port))
> +		return 0;
> +
> +	length = new_mtu + ETH_HLEN + ETH_FCS_LEN;
> +	length += dp->tag_ops->needed_headroom;
> +	length += dp->tag_ops->needed_tailroom;
> +
> +	if (length > RTL8365MB_CFG0_MAX_LEN_MASK)
> +		return -EINVAL;
> +
> +	return regmap_update_bits(priv->map, RTL8365MB_CFG0_MAX_LEN_REG,
> +				  RTL8365MB_CFG0_MAX_LEN_MASK,
> +				  FIELD_PREP(RTL8365MB_CFG0_MAX_LEN_MASK,
> +					     length));
> +}
> +
> +static int rtl8365mb_port_max_mtu(struct dsa_switch *ds, int port)
> +{
> +	return RTL8365MB_CFG0_MAX_LEN_MASK - ETH_HLEN - ETH_FCS_LEN - 8;

Is this 8 because of the Realtek CPU tag length? Luiz and Andrew had some good
comments regarding this. Otherwise I think the patch is OK.

> +}
> +
>  static int rtl8365mb_mib_counter_read(struct realtek_priv *priv, int port,
>  				      u32 offset, u32 length, u64 *mibvalue)
>  {
> @@ -1928,13 +1960,6 @@ static int rtl8365mb_setup(struct dsa_switch *ds)
>  		p->index = i;
>  	}
>  
> -	/* Set maximum packet length to 1536 bytes */
> -	ret = regmap_update_bits(priv->map, RTL8365MB_CFG0_MAX_LEN_REG,
> -				 RTL8365MB_CFG0_MAX_LEN_MASK,
> -				 FIELD_PREP(RTL8365MB_CFG0_MAX_LEN_MASK, 1536));
> -	if (ret)
> -		goto out_teardown_irq;
> -
>  	if (priv->setup_interface) {
>  		ret = priv->setup_interface(ds);
>  		if (ret) {
> @@ -2080,6 +2105,8 @@ static const struct dsa_switch_ops rtl8365mb_switch_ops_smi = {
>  	.phylink_mac_link_down = rtl8365mb_phylink_mac_link_down,
>  	.phylink_mac_link_up = rtl8365mb_phylink_mac_link_up,
>  	.port_stp_state_set = rtl8365mb_port_stp_state_set,
> +	.port_change_mtu = rtl8365mb_port_change_mtu,
> +	.port_max_mtu = rtl8365mb_port_max_mtu,
>  	.get_strings = rtl8365mb_get_strings,
>  	.get_ethtool_stats = rtl8365mb_get_ethtool_stats,
>  	.get_sset_count = rtl8365mb_get_sset_count,
> @@ -2101,6 +2128,8 @@ static const struct dsa_switch_ops rtl8365mb_switch_ops_mdio = {
>  	.phy_read = rtl8365mb_dsa_phy_read,
>  	.phy_write = rtl8365mb_dsa_phy_write,
>  	.port_stp_state_set = rtl8365mb_port_stp_state_set,
> +	.port_change_mtu = rtl8365mb_port_change_mtu,
> +	.port_max_mtu = rtl8365mb_port_max_mtu,
>  	.get_strings = rtl8365mb_get_strings,
>  	.get_ethtool_stats = rtl8365mb_get_ethtool_stats,
>  	.get_sset_count = rtl8365mb_get_sset_count,
> -- 
> 2.30.2
>