linux-kernel - Re: [PATCH net-next v2 1/1] net: dsa: microchip: ksz9477: implement MTU configuration

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Message-ID: <20220225163543.vnqlkltgmwf4vlmm@skbuf>
Date:   Fri, 25 Feb 2022 18:35:43 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Woojung Huh <woojung.huh@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vivien Didelot <vivien.didelot@...il.com>,
        kernel@...gutronix.de, Jakub Kicinski <kuba@...nel.org>,
        UNGLinuxDriver@...rochip.com,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next v2 1/1] net: dsa: microchip: ksz9477: implement
 MTU configuration

On Fri, Feb 25, 2022 at 01:54:30PM +0100, Oleksij Rempel wrote:
> > No bridge, why create a bridge? And even if you do, why add lan5 to it?
> > The expectation is that standalone ports still remain functional when
> > other ports join a bridge.
> 
> No, lan5 is not added to the bridge, but stops functioning after creating
> br with lan1 or any other lanX

Please take time to investigate the problem and fix it.

> > I was saying:
> > 
> > ip link set lan1 up
> > ip link add link lan1 name lan1.5 type vlan id 5
> > ip addr add 172.17.0.2/24 dev lan1.5 && ip link set lan1.5 up
> > iperf3 -c 172.17.0.10
> 
> It works.

This is akin to saying that without any calls to ksz9477_change_mtu(),
just writing VLAN_ETH_FRAME_LEN + ETH_FCS_LEN into REG_SW_MTU__2 is
sufficient to get VLAN-tagged MTU-sized packets to pass through the CPU
port and the lan1 user port.

So my question is: is this necessary?

	if (dsa_is_cpu_port(ds, port))
		new_mtu += KSZ9477_INGRESS_TAG_LEN;