netdev - Re: [PATCH net] net: mscc: ocelot: properly account for VLAN header length when setting MRU

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Message-ID: <CA+h21hrjTFiyNFhFL5vK=0ii7+wdER_kCWObMfSf_G_hP0B5rA@mail.gmail.com>
Date:   Tue, 10 Mar 2020 03:30:26 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Joergen Andreasen <joergen.andreasen@...rochip.com>,
        "Allan W. Nielsen" <allan.nielsen@...rochip.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        netdev <netdev@...r.kernel.org>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Alexandru Marginean <alexandru.marginean@....com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        "Y.b. Lu" <yangbo.lu@....com>
Subject: Re: [PATCH net] net: mscc: ocelot: properly account for VLAN header
 length when setting MRU

On Tue, 10 Mar 2020 at 02:55, David Miller <davem@...emloft.net> wrote:
>
> From: Vladimir Oltean <olteanv@...il.com>
> Date: Mon,  9 Mar 2020 22:16:08 +0200
>
> > From: Vladimir Oltean <vladimir.oltean@....com>
> >
> > What the driver writes into MAC_MAXLEN_CFG does not actually represent
> > VLAN_ETH_FRAME_LEN but instead ETH_FRAME_LEN + ETH_FCS_LEN. Yes they are
> > numerically equal, but the difference is important, as the switch treats
> > VLAN-tagged traffic specially and knows to increase the maximum accepted
> > frame size automatically. So it is always wrong to account for VLAN in
> > the MAC_MAXLEN_CFG register.
> >
> > Unconditionally increase the maximum allowed frame size for
> > double-tagged traffic. Accounting for the additional length does not
> > mean that the other VLAN membership checks aren't performed, so there's
> > no harm done.
> >
> > Also, stop abusing the MTU name for configuring the MRU. There is no
> > support for configuring the MRU on an interface at the moment.
> >
> > Fixes: a556c76adc05 ("net: mscc: Add initial Ocelot switch support")
> > Fixes: fa914e9c4d94 ("net: mscc: ocelot: create a helper for changing the port MTU")
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
>
> This doesn't apply cleanly to the current net tree, please respin.
>
> Thank you.

Ok. Sent new version here:
https://patchwork.ozlabs.org/patch/1251902/
When you merge net into net-next you can use this patch as reference
for the conflict resolution, since it is going to conflict with
69df578c5f4b ("net: mscc: ocelot: eliminate confusion between CPU and
NPI port") - both rename some variables.

Thanks,
-Vladimir