netdev - Question on IGMP snooping on switch managment port

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Date: Mon, 17 Jul 2023 09:32:35 +0200
From: Riccardo Laiolo <laiolo@...ff.it>
To: netdev@...r.kernel.org
Subject: Question on IGMP snooping on switch managment port

Hi,

I'm working on a NXP-based embedded board (imx8mp) with a Marvell mv88e6390 switch.
I'm running Linux 5.15.71 from the NXP downstream git repository (which is a year behind
the upstream 5.15.y LTS release, I think). I've applied all the commits related to the Marvell
driver from the 5.15LTS upstream that I was missing into my codebase.

I can't get the IGMP snooping to works properly. On front facing ports, it appears to work fine:
MDB rules get correctly updated and multicast packets get blocked or routed accordingly. But when
the subscribed is my embedded device (so the subscribed device is the switch
management port) it doesn't work. The first IGMP packet get correctly routed and
propagated through te network and all the interested node update their MDB entry list.

 From now on all the outgoing IGMP packets get dropped.

Adding and removing MDB rules by hand I found the offending rule appears to be
	dev br0 port br0 grp 224.0.1.185 temp

this rule gets correctly appended when I open a multicast rx socket,
but my device fails to answer to any IMGP membership query until I remove said rule.

What am I missing? Is it possible for a linux network switch to be a multicast recipient device?

-- 
Riccardo Laiolo