netdev - Re: [PATCH net-next] net: dsa: mt7530: add support for changing DSA master

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Date:   Sat, 11 Feb 2023 00:27:21 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Richard van Schagen <richard@...terhints.com>
Cc:     "arinc9.unal@...il.com" <arinc9.unal@...il.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Arınç ÜNAL <arinc.unal@...nc9.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "erkin.bozoglu@...ont.com" <erkin.bozoglu@...ont.com>
Subject: Re: [PATCH net-next] net: dsa: mt7530: add support for changing DSA
 master

On Fri, Feb 10, 2023 at 09:41:06PM +0000, Richard van Schagen wrote:
> > I believe you need to reject LAG DSA masters.
> 
> Not sure what you mean: how is this different from the change_master in the Felix driver when using 8021q tags?
> But. Can add a check if you prefer. It might be a good idea anyway to be future proof. The MT7531 has support for LAG in hw.

I mean, like Documentation/networking/dsa/configuration.rst says, that the user can attempt
to put the DSA masters in a LAG and create a larger DSA master which is that bonding device.

The difference from the Felix driver is that Felix supports LAG DSA masters and this driver doesn't.

I don't believe there is any other restriction in the code which would prevent a driver which
implements port_change_master() from accepting that as a valid configuration, so it's going to
be the mt7530 driver who acts as the final frontier in this case.

An "if (netif_is_lag_master(master)) return -EOPNOTSUPP" will do. But it would always be good
to check if it's really needed :)