netdev - Re: [PATCH net 3/3] net: dsa: Include tagger overhead when setting MTU for DSA and CPU ports

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Date:   Tue, 25 May 2021 04:53:39 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        "cao88yu@...il.com" <cao88yu@...il.com>
Subject: Re: [PATCH net 3/3] net: dsa: Include tagger overhead when setting
 MTU for DSA and CPU ports

On Mon, May 24, 2021 at 10:04:01PM +0000, Vladimir Oltean wrote:
> On Mon, May 24, 2021 at 11:33:13PM +0200, Andrew Lunn wrote:
> > Same members of the Marvell Ethernet switches impose MTU restrictions
> > on ports used for connecting to the CPU or DSA. If the MTU is set too
> > low, tagged frames will be discarded. Ensure the tagger overhead is
> > included in setting the MTU for DSA and CPU ports.
> > 
> > Fixes: 1baf0fac10fb ("net: dsa: mv88e6xxx: Use chip-wide max frame size for MTU")
> > Reported by: 曹煜 <cao88yu@...il.com>
> > Signed-off-by: Andrew Lunn <andrew@...n.ch>
> > ---
> 
> Some switches account for the DSA tag automatically in hardware. So far
> it has been the convention that if a switch doesn't do that, the driver
> should, not DSA.

O.K.

This is going to be a little bit interesting with Tobias's support for
changing the tag protocol. I need to look at the ordering.

	 Andrew