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Date:   Wed, 24 May 2023 14:53:57 +0200
From:   Lukasz Majewski <lukma@denx.de>
To:     "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc:     Andrew Lunn <andrew@lunn.ch>, Vladimir Oltean <olteanv@gmail.com>,
        Eric Dumazet <edumazet@google.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Alexander Duyck <alexander.duyck@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 1/3] dsa: marvell: Define .set_max_frame_size()
 function for mv88e6250 SoC family
Message-ID: <20230524145357.3928f261@wsk>
In-Reply-To: <ZGzP0qEjQkCFnXnr@shell.armlinux.org.uk>
References: <20230523142912.2086985-1-lukma@denx.de>
        <20230523142912.2086985-2-lukma@denx.de>
        <ZGzP0qEjQkCFnXnr@shell.armlinux.org.uk>
Organization: denx.de
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Hi Russell,

> On Tue, May 23, 2023 at 04:29:10PM +0200, Lukasz Majewski wrote:
> > Switches from mv88e6250 family (the marketing name - "Link Street",
> > including mv88e6020 and mv88e6071) need the possibility to setup the
> > maximal frame size, as they support frames up to 2048 bytes.
> >=20
> > Signed-off-by: Lukasz Majewski <lukma@denx.de> =20
>=20
> Adding this function doesn't allow the "possibility" for a larger
> frame size. Adding it changes the value returned from
> mv88e6xxx_get_max_mtu() to be a larger frame size, so all switches
> that make use of mv88e6250_ops will be expected to support this
> larger frame size. Do we know whether that is true?
>=20

According to functional specification - the 6070, 6071, 6250, 6020 and
6220 have "Max Frame Size" of 2048 bytes.

The mv88e6xxx_get_max_mtu() now will:
return 1632 - VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN;

which is acceptable and safe for this family of chips.

> There were patches floating about a while ago that specified the
> maximum size in struct mv88e6xxx_info, but it seems those died a
> death.
>=20

Those patches seems to not be strictly required after Vladimir's work.

The v7 provides what I need, so yes - extra patches from v6 can be
discarded.


Best regards,

Lukasz Majewski

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