netdev - Re: [PATCH v3 net] net: ftmac100: support frames with DSA tag

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Message-ID: <CABikg9zmmSysguNTXmM7cG8KqKBoEKshLKUCb5o_kpNqFm2KRA@mail.gmail.com>
Date:   Wed, 19 Oct 2022 19:19:11 +0300
From:   Sergei Antonov <saproj@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH v3 net] net: ftmac100: support frames with DSA tag

On Mon, 17 Oct 2022 at 18:55, Vladimir Oltean <olteanv@...il.com> wrote:
> 6. Actually implement the ndo_change_mtu() for this driver, and even though you
>    don't make any hardware change based on the precise value, you could do one
>    important thing. Depending on whether the dev->mtu is <= 1500 or not, you could
>    set or unset the FTL bit, and this could allow for less CPU cycles spent
>    dropping S/G frames when the MTU of the interface is standard 1500.

Can I do the mtu>1500 check and set FTL in ndo_open() (which is called
after ndo_change_mtu())? I am submitting a v4 of the patch, and your
feedback to it would be helpful. I got rid of all mentions of DSA
tagging there, so patch description and a code comment are new. Thanks
for clearing things up regarding EtherType 0800.

> With these changes, you would leave the ftmac100 driver in a more civilized
> state, you wouldn't need to implement S/G RX unless you wanted to, and
> as a side effect, it would also operate well as a DSA master.

What does S/G stand for?