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Date:   Fri, 13 Jan 2023 14:20:17 +0100
From:   Lukasz Majewski <lukma@denx.de>
To:     Vladimir Oltean <olteanv@gmail.com>
Cc:     Andrew Lunn <andrew@lunn.ch>, Eric Dumazet <edumazet@google.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Paolo Abeni <pabeni@redhat.com>,
        Alexander Duyck <alexander.duyck@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 1/3] dsa: marvell: Provide per device information
 about max frame size
Message-ID: <20230113142017.78184ce1@wsk>
In-Reply-To: <20230113122754.52qvl3pvwpdy5iqk@skbuf>
References: <20230106101651.1137755-1-lukma@denx.de>
        <20230106101651.1137755-1-lukma@denx.de>
        <20230106145109.mrv2n3ppcz52jwa2@skbuf>
        <20230113131331.28ba7997@wsk>
        <20230113122754.52qvl3pvwpdy5iqk@skbuf>
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Hi Vladimir,

> On Fri, Jan 13, 2023 at 01:13:31PM +0100, Lukasz Majewski wrote:
> > I think that this commit [1], made the adjustment to fix yet another
> > issue.
> > [1] -
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/comm=
it/?id=3Db9c587fed61cf88bd45822c3159644445f6d5aa6
> > =20
>=20
> It appears that this is the commit to blame, indeed.
>=20
> > It looks like the missing 8 bytes are added in the
> > mv88e6xxx_change_mtu() function. =20
>=20
> Only for DSA and CPU ports. The driver still behaves as if the max MTU
> on user ports is 1492 bytes.
>=20

It looks so...

> > > I wonder, shouldn't we first fix that, and apply this patch set
> > > afterwards? =20
> >=20
> > IMHO, it is up to Andrew to decide how to proceed, as the
> > aforementioned patch [1] is an attempt to fix yet another issue [2].
> > [2] -
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/comm=
it/?id=3D1baf0fac10fbe3084975d7cb0a4378eb18871482
> > =20
>=20
> I think the handling for those switches were neither
> port_set_jumbo_size() nor set_max_frame_size() is present is just a
> roundabout way of saying "hey, I only support ETH_DATA_LEN MTU and
> can't change it, leave me alone". But it isn't what the code does.

I tend to agree... The number of switched which suppor 1522 B max frame
is only six. This may be why the problem was not noticed.

The fixed function maybe should look like below:


static int mv88e6xxx_get_max_mtu(struct dsa_switch *ds, int port)
{
	....

=09
	int max_mtu;

	max_mtu =3D chip->info->max_frame_size - VLAN_ETH_HLEN -
		  ETH_FCS_LE;

	if (dsa_is_dsa_port(ds, port) || dsa_is_cpu_port(ds, port))
		  max_mtu -=3D EDSA_HLEN;

	return max_mtu;
}

Comments more than welcome.


Best regards,

Lukasz Majewski

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