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

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Message-ID: <b01fb27b-2d8d-4652-8f64-cbda79bcd266@gmail.com>
Date: Mon, 11 Dec 2023 13:24:03 -0800
From: Florian Fainelli <f.fainelli@...il.com>
To: Linus Walleij <linus.walleij@...aro.org>,
 Alvin Šipraga <alsi@...g-olufsen.dk>,
 Andrew Lunn <andrew@...n.ch>, Vladimir Oltean <olteanv@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] net: dsa: realtek: Rewrite RTL8366RB MTU
 handling

On 12/9/23 14:37, 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>

Reviewed-by: Florian Fainelli <florian.fainelli@...adcom.com>
-- 
Florian