netdev - Re: [PATCH net 1/1] net: stmmac: Prevent DSA tags from breaking COE

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Date: Tue, 19 Dec 2023 15:19:45 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: Vladimir Oltean <olteanv@...il.com>, Romain Gantois <romain.gantois@...tlin.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Jose Abreu <joabreu@...opsys.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Maxime Coquelin <mcoquelin.stm32@...il.com>, Miquel Raynal <miquel.raynal@...tlin.com>, 
	Sylvain Girard <sylvain.girard@...com>, Pascal EBERHARD <pascal.eberhard@...com>, 
	Richard Tresidder <rtresidd@...ctromag.com.au>, netdev@...r.kernel.org, 
	linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org
Subject: Re: [PATCH net 1/1] net: stmmac: Prevent DSA tags from breaking COE

On Tue, Dec 19, 2023 at 2:07 PM Maxime Chevallier
<maxime.chevallier@...tlin.com> wrote:

> So it looks like an acceptable solution would be something along the
> lines of what Linus is suggesting here :
>
> https://lore.kernel.org/netdev/20231216-new-gemini-ethernet-regression-v2-2-64c269413dfa@linaro.org/
>
> If so, maybe it's worth adding a new helper for that check ?

Yeah it's a bit annoying when skb->protocol is not == ethertype of buffer.

I can certainly add a helper such as skb_eth_raw_ethertype()
to <linux/if_ether.h> that will inspect the actual ethertype in
skb->data.

It's the most straight-forward approach.

We could also add something like bool custom_ethertype; to
struct sk_buff and set that to true if the tagger adds a custom
ethertype. But I don't know how the network developers feel about
that.

Yours,
Linus Walleij