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Date:   Tue, 3 Aug 2021 14:33:04 +0200
From:   Arnd Bergmann <>
To:     Vladimir Oltean <>
Cc:     Grygorii Strashko <>,
        Networking <>,
        Jakub Kicinski <>,
        "David S. Miller" <>,
        Naresh Kamboju <>,
        Lars Povlsen <>,
        Steen Hegelund <>,
        Microchip Linux Driver Support <>,
        Florian Fainelli <>,
        Andrew Lunn <>,
        Vivien Didelot <>,
        Ido Schimmel <>, Jiri Pirko <>,
        Roopa Prabhu <>,
        Nikolay Aleksandrov <>,
        Linux Kernel Functional Testing <>,
        Vignesh Raghavendra <>
Subject: Re: [PATCH net-next] net: build all switchdev drivers as modules when
 the bridge is a module

On Tue, Aug 3, 2021 at 1:58 PM Vladimir Oltean <> wrote:
> On Tue, Aug 03, 2021 at 02:18:38PM +0300, Grygorii Strashko wrote:
> > In my opinion, the problem is a bit bigger here than just fixing the build :(
> >
> > In case, of ^cpsw the switchdev mode is kinda optional and in many cases
> > (especially for testing purposes, NFS) the multi-mac mode is still preferable mode.
> >
> > There were no such tight dependency between switchdev drivers and bridge core before and switchdev serviced as
> > independent, notification based layer between them, so ^cpsw still can be "Y" and bridge can be "M".
> > Now for mostly every kernel build configuration the CONFIG_BRIDGE will need to be set as "Y", or we will have
> > to update drivers to support build with BRIDGE=n and maintain separate builds for networking vs non-networking testing.
> > But is this enough? Wouldn't it cause 'chain reaction' required to add more and more "Y" options (like CONFIG_VLAN_8021Q)?
> >
> > PS. Just to be sure we on the same page - ARM builds will be forced (with this patch) to have CONFIG_TI_CPSW_SWITCHDEV=m
> > and so all our automation testing will just fail with omap2plus_defconfig.
> I didn't realize it is such a big use case to have the bridge built as
> module and cpsw as built-in.

I don't think anybody realistically cares about doing, I was only interested in
correctly expressing what the dependency is.

> I will send a patch that converts the
> switchdev_bridge_port_{,un}offload functions to simply emit a blocking
> switchdev notifier which the bridge processes (a la SWITCHDEV_FDB_ADD_TO_BRIDGE),
> therefore making switchdev and the bridge loosely coupled in order to
> keep your setup the way it was before.

That does sounds like it can avoid future build regressions, and simplify the
Kconfig dependencies, so that would probably be a good solution.


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