linux-kernel - Re: [PATCH v2 net-next 2/6] net: dsa: propagate flags down towards drivers

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Date:   Thu, 30 Mar 2023 18:07:52 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Hans Schultz <netdev@...io-technology.com>
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Woojung Huh <woojung.huh@...rochip.com>,
        "maintainer:MICROCHIP KSZ SERIES ETHERNET SWITCH DRIVER" 
        <UNGLinuxDriver@...rochip.com>, Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Clément Léger <clement.leger@...tlin.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Shuah Khan <shuah@...nel.org>,
        Christian Marangi <ansuelsmth@...il.com>,
        Ido Schimmel <idosch@...dia.com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        "open list:RENESAS RZ/N1 A5PSW SWITCH DRIVER" 
        <linux-renesas-soc@...r.kernel.org>,
        "moderated list:ETHERNET BRIDGE" <bridge@...ts.linux-foundation.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 net-next 2/6] net: dsa: propagate flags down towards
 drivers

On Thu, Mar 30, 2023 at 04:54:19PM +0200, Hans Schultz wrote:
> I don't know if you have a solution in mind wrt the behaviour of the
> offloaded flag if it is not to do as it does now and let the bridge age
> out dynamic entries. That led me to conclude that this patch-set cannot
> use the offloaded flag, but you seem to suggest otherwise.
> 
> If you have a suggestion, feel free.

Didn't I explain what I would do from the first reply on this thread?
https://patchwork.kernel.org/project/netdevbpf/patch/20230318141010.513424-3-netdev@kapio-technology.com/#25270613

As a bug fix, stop reporting to switchdev those FDB entries with
BR_FDB_ADDED_BY_USER && !BR_FDB_STATIC. Then, after "net" is merged into
"net-next" next Thursday (the ship has sailed for today), add "bool static"
to the switchdev notifier info, and make all switchdev drivers (everywhere
where a SWITCHDEV_FDB_ADD_TO_DEVICE handler appears) ignore the
"added_by_user && !is_static" combination, but by their own choice and
not by switchdev's choice.

Then, make DSA decide whether to handle the "added_by_user && !is_static"
combination or not, based on the presence of the DSA_FDB_FLAG_DYNAMIC
flag, which will be set in ds->supported_fdb_flags only for the mv88e6xxx
driver. When DSA_FDB_FLAG_DYNAMIC is not supported, DSA will not offload
the FDB entry: neither will it call port_fdb_add(), nor will it emit
SWITCHDEV_FDB_OFFLOADED. Ideally, it would also inform user space that
it can't offload this flag by returning an error, but the lack of an
error propagation mechanism from switchdev to the bridge FDB is a known
limitation which is hard to overcome, and is outside the scope of your
patchset I believe. To see whether DSA has acted upon the "master dynamic"
flag or not, it would be good enough for the user to see something
adequate in "bridge fdb show | grep offloaded", I believe.