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

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Date:   Mon, 9 May 2022 03:45:11 -0300
From:   Luiz Angelo Daros de Luca <luizluca@...il.com>
To:     Hauke Mehrtens <hauke@...ke-m.de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>
Subject: Re: [PATCH 3/4] net: dsa: realtek: rtl8365mb: Add setting MTU

> 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
> 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
> +        * 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;

Isn't it better to keep that within the driver? No matter the tag
position, it will be either 4 (RTL8365MB_CPU_FORMAT_4BYTES) or 8
(RTL8365MB_CPU_FORMAT_8BYTES) bytes. You can retrieve that from
priv->chip_data->cpu->format, but the driver will probably never
support RTL8365MB_CPU_FORMAT_4BYTES. Until someone does implement the
4-bytes tag (for some mysterious reason), I believe we could simply
use a constant here (using a proper new macro).

> +
> +       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;

What is this magic 8? RTL8_4_TAG_LEN?

> +}
> +
>  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
>