netdev - Re: [PATCH net-next] net: dsa: mt7530: enable MTU normalization

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Date:   Fri, 11 Dec 2020 21:11:51 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     DENG Qingfang <dqfext@...il.com>
Cc:     netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH net-next] net: dsa: mt7530: enable MTU normalization

On Fri, Dec 11, 2020 at 01:03:22AM +0800, DENG Qingfang wrote:
> MT7530 has a global RX length register, so we are actually changing its
> MRU.
> Enable MTU normalization for this reason.
>
> Signed-off-by: DENG Qingfang <dqfext@...il.com>
> ---

Makes sense. Since it's global and not per port, this also helps the
stack to be aware of the fact that all bridged interfaces have the same
MTU. We could probably do a little bit better by also informing the
standalone interfaces about the updated MTU, but since the value that we
program into the standalone ports is >= than what the stack knows about,
there isn't an issue really.

Reviewed-by: Vladimir Oltean <olteanv@...il.com>

>  drivers/net/dsa/mt7530.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> index 99bf8fed6536..a67cac15a724 100644
> --- a/drivers/net/dsa/mt7530.c
> +++ b/drivers/net/dsa/mt7530.c
> @@ -1657,6 +1657,7 @@ mt7530_setup(struct dsa_switch *ds)
>  	 */
>  	dn = dsa_to_port(ds, MT7530_CPU_PORT)->master->dev.of_node->parent;
>  	ds->configure_vlan_while_not_filtering = true;
> +	ds->mtu_enforcement_ingress = true;
>
>  	if (priv->id == ID_MT7530) {
>  		regulator_set_voltage(priv->core_pwr, 1000000, 1000000);
> @@ -1895,6 +1896,7 @@ mt7531_setup(struct dsa_switch *ds)
>  	}
>
>  	ds->configure_vlan_while_not_filtering = true;
> +	ds->mtu_enforcement_ingress = true;
>
>  	/* Flush the FDB table */
>  	ret = mt7530_fdb_cmd(priv, MT7530_FDB_FLUSH, NULL);
> --
> 2.25.1
>