netdev - Re: [RFC PATCH net-next 00/12] DSA changes for multiple CPU ports (part 3)

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Message-ID: <20220524122905.4y5kbpdjwvb6ee4p@skbuf>
Date:   Tue, 24 May 2022 12:29:06 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Ansuel Smith <ansuelsmth@...il.com>
CC:     Vladimir Oltean <olteanv@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        Marek Behún <kabel@...nel.org>,
        DENG Qingfang <dqfext@...il.com>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Colin Foster <colin.foster@...advantage.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Luiz Angelo Daros de Luca <luizluca@...il.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Frank Wunderlich <frank-w@...lic-files.de>
Subject: Re: [RFC PATCH net-next 00/12] DSA changes for multiple CPU ports
 (part 3)

On Tue, May 24, 2022 at 02:02:19PM +0200, Ansuel Smith wrote:
> Probably offtopic but I wonder if the use of a LAG as master can
> cause some problem with configuration where the switch use a mgmt port
> to send settings. Wonder if with this change we will have to introduce
> an additional value to declare a management port that will be used since
> master can now be set to various values. Or just the driver will have to
> handle this with its priv struct (think this is the correct solution)
> 
> I still have to find time to test this with qca8k.

Not offtopic, this is a good point. dsa_tree_master_admin_state_change()
and dsa_tree_master_oper_state_change() set various flags in cpu_dp =
master->dsa_ptr. It's unclear if the cpu_dp we assign to a LAG should
track the admin/oper state of the LAG itself or of the physical port.
Especially since the lag->dsa_ptr is the same as one of the master->dsa_ptr.
It's clear that the same structure can't track both states. I'm thinking
we should suppress the NETDEV_CHANGE and NETDEV_UP monitoring from slave.c
on LAG DSA masters, and track only the physical ones. In any case,
management traffic does not really benefit from being sent/received over
a LAG, and I'm thinking we should just use the physical port.
Your qca8k_master_change() function explicitly only checks for CPU port
0, which in retrospect was a very wise decision in terms of forward
compatibility with device trees with multiple CPU ports.