netdev - Re: [PATCH RFC net-next 00/10] MC Flood disable and snooping

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Message-ID: <f5512e7b-b572-4444-9d56-1eed9bbcda6b@lunn.ch>
Date: Tue, 2 Apr 2024 14:43:18 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Joseph Huang <Joseph.Huang@...min.com>
Cc: netdev@...r.kernel.org, Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Roopa Prabhu <roopa@...dia.com>,
	Nikolay Aleksandrov <razor@...ckwall.org>,
	Linus Lüssing <linus.luessing@...3.blue>,
	linux-kernel@...r.kernel.org, bridge@...ts.linux.dev
Subject: Re: [PATCH RFC net-next 00/10] MC Flood disable and snooping

On Mon, Apr 01, 2024 at 08:10:59PM -0400, Joseph Huang wrote:
> There is a use case where one would like to enable multicast snooping
> on a bridge but disable multicast flooding on all bridge ports so that
> registered multicast traffic will only reach the intended recipients and
> unregistered multicast traffic will be dropped. However, with existing
> bridge ports' mcast_flood flag implementation, it doesn't work as desired.
> 
> This patchset aims to make multicast snooping work even when multicast
> flooding is disabled on the bridge ports, without changing the semantic of
> the mcast_flood flag too much. Patches 1 to 4 attempt to address this issue.
> 
> Also, in a network where more than one multicast snooping capable bridges
> are interconnected without multicast routers being present, multicast
> snooping fails if:
> 
>   1. The source is not directly attached to the Querier
>   2. The listener is beyond the mrouter port of the bridge where the
>      source is directly attached
>   3. A hardware offloading switch is involved

I've not studied the details here, but that last point makes me think
the offload driver is broken. There should not be any difference
between software bridging and hardware bridging. The whole idea is
that you take what Linux can do in software and accelerate it by
offloading to hardware. Doing acceleration should not change the
behaviour.

> The patches were developed against 5.15, and forward-ported to 6.8.
> Tests were done on a Pi 4B + Marvell 6393X Eval board with a single
> switch chip with no VLAN.

So what is the mv88e6xxx driver doing wrong?

	Andrew