netdev - Re: [RFC net-next 2/3] net: dsa: qca8k: enable assisted learning on CPU port

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Message-ID: <20210807222555.y6r7qxhdyy6d3esx@skbuf>
Date:   Sun, 8 Aug 2021 01:25:55 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     DENG Qingfang <dqfext@...il.com>
Cc:     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>,
        Russell King <linux@...linux.org.uk>,
        "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Ansuel Smith <ansuelsmth@...il.com>,
        Jonathan McDowell <noodles@...th.li>,
        Michal Vokáč <vokac.m@...il.com>,
        Christian Lamparter <chunkeey@...il.com>,
        Nishka Dasgupta <nishkadg.linux@...il.com>,
        Xiaofei Shen <xiaofeis@...eaurora.org>,
        John Crispin <john@...ozen.org>,
        Stefan Lippers-Hollmann <s.l-h@....de>,
        Hannu Nyman <hannu.nyman@....fi>,
        Imran Khan <gururug@...il.com>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        Nick Lowe <nick.lowe@...il.com>,
        André Valentin <avalentin@....kalnet.hooya.de>
Subject: Re: [RFC net-next 2/3] net: dsa: qca8k: enable assisted learning on
 CPU port

On Sat, Aug 07, 2021 at 08:07:25PM +0800, DENG Qingfang wrote:
> Enable assisted learning on CPU port to fix roaming issues.

'roaming issues' implies to me it suffered from blindness to MAC
addresses learned on foreign interfaces, which appears to not be true
since your previous patch removes hardware learning on the CPU port
(=> hardware learning on the CPU port was supported, so there were no
roaming issues)

> 
> Although hardware learning is available, it won't work well with
> software bridging fallback or multiple CPU ports.

This part is potentially true however, but it would need proof. I am not
familiar enough with the qca8k driver to say for sure that it suffers
from the typical problem with bridging with software LAG uppers (no FDB
isolation for standalone ports => attempt to shortcircuit the forwarding
through the CPU port and go directly towards the bridged port, which
would result in drops), and I also can't say anything about its support
for multiple CPU ports.