netdev - Re: [PATCH v4 1/3] dsa: marvell: Provide per device information about max frame size

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Date:   Fri, 13 Jan 2023 14:27:54 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Lukasz Majewski <lukma@...x.de>
Cc:     Andrew Lunn <andrew@...n.ch>, Eric Dumazet <edumazet@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] dsa: marvell: Provide per device information
 about max frame size

On Fri, Jan 13, 2023 at 01:13:31PM +0100, Lukasz Majewski wrote:
> I think that this commit [1], made the adjustment to fix yet another
> issue.
> [1] -
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b9c587fed61cf88bd45822c3159644445f6d5aa6

It appears that this is the commit to blame, indeed.

> It looks like the missing 8 bytes are added in the
> mv88e6xxx_change_mtu() function.

Only for DSA and CPU ports. The driver still behaves as if the max MTU
on user ports is 1492 bytes.

> > I wonder, shouldn't we first fix that, and apply this patch set
> > afterwards?
> 
> IMHO, it is up to Andrew to decide how to proceed, as the
> aforementioned patch [1] is an attempt to fix yet another issue [2].
> [2] -
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1baf0fac10fbe3084975d7cb0a4378eb18871482

I think the handling for those switches were neither port_set_jumbo_size()
nor set_max_frame_size() is present is just a roundabout way of saying
"hey, I only support ETH_DATA_LEN MTU and can't change it, leave me alone".
But it isn't what the code does.