netdev - Re: [PATCH net-next 5/5 v2] net: gemini: Indicate that we can handle jumboframes

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Date:   Wed, 11 Jul 2018 21:10:21 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Michal Miroslaw <mirq-linux@...e.qmqm.pl>,
        Florian Fainelli <f.fainelli@...il.com>,
        Paulius Zaleckas <paulius.zaleckas@...il.com>,
        Hans Ulli Kroll <ulli.kroll@...glemail.com>,
        Janos Laube <janos.dev@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH net-next 5/5 v2] net: gemini: Indicate that we can handle jumboframes

On Wed, Jul 4, 2018 at 10:35 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> On Wed, Jul 04, 2018 at 08:33:24PM +0200, Linus Walleij wrote:
> > The hardware supposedly handles frames up to 10236 bytes and
> > implements .ndo_change_mtu() so accept 10236 minus the ethernet
> > header for a VLAN tagged frame on the netdevices. Use
> > ETH_MIN_MTU as minimum MTU.
> >
> > Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
>
> Hi Linus
>
> Did you try with an MTU of 68? Maybe the vendor picked 256 because of
> a hardware limit?

Yeah works fine:

ping -s 68 169.254.1.2
PING 169.254.1.2 (169.254.1.2) 68(96) bytes of data.
76 bytes from 169.254.1.2: icmp_seq=1 ttl=64 time=0.359 ms
76 bytes from 169.254.1.2: icmp_seq=2 ttl=64 time=0.346 ms
76 bytes from 169.254.1.2: icmp_seq=3 ttl=64 time=0.351 ms

This also works fine:

ping -s 9000 169.254.1.2
PING 169.254.1.2 (169.254.1.2) 9000(9028) bytes of data.
9008 bytes from 169.254.1.2: icmp_seq=1 ttl=64 time=1.45 ms
9008 bytes from 169.254.1.2: icmp_seq=2 ttl=64 time=1.68 ms
9008 bytes from 169.254.1.2: icmp_seq=3 ttl=64 time=1.55 ms

I'll send new patches with all suggested changes soon :)

Thanks a lot for your help!

Yours,
Linus Walleij