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

From: Vladimir Oltean <vladimir.oltean@nxp.com>
To: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Arnd Bergmann <arnd@kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Jakub Kicinski <kuba@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Naresh Kamboju <naresh.kamboju@linaro.org>,
	Lars Povlsen <lars.povlsen@microchip.com>,
	Steen Hegelund <Steen.Hegelund@microchip.com>,
	Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Ido Schimmel <idosch@nvidia.com>, Jiri Pirko <jiri@nvidia.com>,
	Roopa Prabhu <roopa@nvidia.com>,
	Nikolay Aleksandrov <nikolay@nvidia.com>,
	Linux Kernel Functional Testing <lkft@linaro.org>,
	Vignesh Raghavendra <vigneshr@ti.com>
Subject: Re: [PATCH net-next] net: build all switchdev drivers as modules when the bridge is a module
Date: Tue, 3 Aug 2021 11:58:19 +0000	[thread overview]
Message-ID: <20210803115819.sdtdqhmfk5k4olip@skbuf> (raw)
In-Reply-To: <eab61b8f-fc54-ea63-ad31-73fb13026b1f@ti.com>

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 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.