netdev - Re: [RFC net-next 0/2] mt7530 software fallback bridging fix

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Date:   Wed, 28 Jul 2021 21:08:19 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     DENG Qingfang <dqfext@...il.com>
Cc:     Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC net-next 0/2] mt7530 software fallback bridging fix

On Thu, Jul 29, 2021 at 01:53:24AM +0800, DENG Qingfang wrote:
> DSA core has gained software fallback support since commit 2f5dc00f7a3e,
> but it does not work properly on mt7530. This patch series fixes the
> issues.

I haven't looked at the patches, just read the commit messages. Your
approach makes sense considering that mt7530 supports ACL rules. For
switches that don't, I was thinking that we could add a check within DSA
that bridging with software uppers such as LAGs can be allowed only as
long as the bridge is VLAN-aware. If it is, then the classified VLAN for
packets on standalone ports can be made == 0, and if independent VLAN
learning is used, then the FDB entries learned on bridged ports will
always have a VLAN ID != 0, so the standalone switch port won't attempt
to shortcircuit the forwarding process towards the bridge port.
Anyway, we can have both solutions, yours and the generic DSA restriction.
I was just not expecting to see a fix for this already, it makes me
think that the DSA restriction for VLAN-unaware software bridging should
not be unconditional, but we should guard it behind a new bool option
like ds->fdb_shared_across_all_ports = true or something like that.
What do you think?