netdev - Re: [PATCH net-next 2/2] net: dsa: realtek: Rewrite RTL8366RB MTU handling

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Date: Tue, 12 Dec 2023 14:18:27 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Linus Walleij <linus.walleij@...aro.org>, Alvin Šipraga
 <alsi@...g-olufsen.dk>, Andrew Lunn <andrew@...n.ch>, Florian Fainelli
 <f.fainelli@...il.com>, Vladimir Oltean <olteanv@...il.com>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] net: dsa: realtek: Rewrite RTL8366RB MTU
 handling

On Tue, 2023-12-12 at 14:16 +0100, Paolo Abeni wrote:
> On Sat, 2023-12-09 at 23:37 +0100, Linus Walleij wrote:
> > The MTU callbacks are in layer 1 size, so for example 1500
> > bytes is a normal setting. Cache this size, and only add
> > the layer 2 framing right before choosing the setting. On
> > the CPU port this will however include the DSA tag since
> > this is transmitted from the parent ethernet interface!
> > 
> > Add the layer 2 overhead such as ethernet and VLAN framing
> > and FCS before selecting the size in the register.
> > 
> > This will make the code easier to understand.
> > 
> > The rtl8366rb_max_mtu() callback returns a bogus MTU
> > just subtracting the CPU tag, which is the only thing
> > we should NOT subtract. Return the correct layer 1
> > max MTU after removing headers and checksum.
> > 
> > Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> 
> FTR, my understanding is that the possible MTU API changes still under
> discussion, are somewhat orthogonal to this patch, which is suitable
> as-is for net.

Typo above -> 'net-next'.

> 
> I'm applying this fixes right now.
> 
> Cheers,
> 
> Paolo