netdev - Re: [PATCH net-next] net: build all switchdev drivers as modules when the bridge is a module

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Date:   Mon, 2 Aug 2021 16:47:25 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     Networking <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Ido Schimmel <idosch@...dia.com>, Jiri Pirko <jiri@...dia.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Linux Kernel Functional Testing <lkft@...aro.org>
Subject: Re: [PATCH net-next] net: build all switchdev drivers as modules when
 the bridge is a module

On Mon, Jul 26, 2021 at 4:28 PM Vladimir Oltean <vladimir.oltean@....com> wrote:
>
> Currently, all drivers depend on the bool CONFIG_NET_SWITCHDEV, but only
> the drivers that call some sort of function exported by the bridge, like
> br_vlan_enabled() or whatever, have an extra dependency on CONFIG_BRIDGE.
>
> Since the blamed commit, all switchdev drivers have a functional
> dependency upon switchdev_bridge_port_{,un}offload(), which is a pair of
> functions exported by the bridge module and not by the bridge-independent
> part of CONFIG_NET_SWITCHDEV.
>
> Problems appear when we have:
>
> CONFIG_BRIDGE=m
> CONFIG_NET_SWITCHDEV=y
> CONFIG_TI_CPSW_SWITCHDEV=y
>
> because cpsw, am65_cpsw and sparx5 will then be built-in but they will
> call a symbol exported by a loadable module. This is not possible and
> will result in the following build error:
>
> drivers/net/ethernet/ti/cpsw_new.o: in function `cpsw_netdevice_event':
> drivers/net/ethernet/ti/cpsw_new.c:1520: undefined reference to
>                                         `switchdev_bridge_port_offload'
> drivers/net/ethernet/ti/cpsw_new.c:1537: undefined reference to
>                                         `switchdev_bridge_port_unoffload'
>
> As mentioned, the other switchdev drivers don't suffer from this because
> switchdev_bridge_port_offload() is not the first symbol exported by the
> bridge that they are calling, so they already needed to deal with this
> in the same way.
>
> Fixes: 2f5dc00f7a3e ("net: bridge: switchdev: let drivers inform which bridge ports are offloaded")
> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

I'm still seeing build failures after this patch was applied. I have a fixup
patch that seems to work, but I'm still not sure if that version is complete.

      Arnd