netdev - Re: [PATCH v5 net-next] net: ftmac100: support mtu

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Message-ID: <CABikg9z5uuo9qdcuR4p29Y6W=rGBQedUV4GWB2C+6=6APAtTNQ@mail.gmail.com>
Date:   Thu, 27 Oct 2022 19:59:11 +0300
From:   Sergei Antonov <saproj@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     netdev@...r.kernel.org, andrew@...n.ch, pabeni@...hat.com,
        kuba@...nel.org, edumazet@...gle.com, davem@...emloft.net
Subject: Re: [PATCH v5 net-next] net: ftmac100: support mtu > 1500

On Thu, 27 Oct 2022 at 14:35, Vladimir Oltean <olteanv@...il.com> wrote:
>
> Hi Sergei,
>
> On Mon, Oct 24, 2022 at 08:58:23PM +0300, Sergei Antonov wrote:
> > The ftmac100 controller considers packets >1518 (1500 + Ethernet + FCS)
> > FTL (frame too long) and drops them. That is fine with mtu 1500 or less
> > and it saves CPU time. When DSA is present, mtu is bigger (for VLAN
> > tagging) and the controller's built-in behavior is not desired then. We
> > can make the controller deliver FTL packets to the driver by setting
> > FTMAC100_MACCR_RX_FTL. Then we have to check ftmac100_rxdes_frame_length()
> > (packet length sans FCS) on packets marked with FTMAC100_RXDES0_FTL flag.
> >
> > Check for mtu > 1500 in .ndo_open() and set FTMAC100_MACCR_RX_FTL to let
> > the driver FTL packets. Implement .ndo_change_mtu() and check for
> > mtu > 1500 to set/clear FTMAC100_MACCR_RX_FTL dynamically.
> >
> > Fixes: 8d77c036b57c ("net: add Faraday FTMAC100 10/100 Ethernet driver")
> > Signed-off-by: Sergei Antonov <saproj@...il.com>
> > ---
>
> I think it's clear there are problems in communication between us, so
> let me try differently.
>
> Does the attached series of 3 patches work for you? I only compile
> tested them.

I have tested your patches. They fix the problem I have. If they can
make it into mainline Linux - great. Thanks for your help!

A remark on 0002-net-ftmac100-report-the-correct-maximum-MTU-of-1500.patch:
I can not make a case for VLAN_ETH_HLEN because it includes 4 bytes
from a switch and ftmac100 is not always used with a switch.