netdev - Re: [PATCH net-next] net: dsa: tag_rtl4_a: Drop bit 9 from egress frames

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Message-ID: <20210923222549.byri6ch2kcvowtv4@skbuf>
Date:   Fri, 24 Sep 2021 01:25:49 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     DENG Qingfang <dqfext@...il.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>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: dsa: tag_rtl4_a: Drop bit 9 from egress
 frames

On Fri, Sep 24, 2021 at 12:21:39AM +0200, Linus Walleij wrote:
> On Fri, Sep 24, 2021 at 12:12 AM Vladimir Oltean <olteanv@...il.com> wrote:
> 
> > > Hm I suspect it disable learning on RTL8366RB as well.
> >
> > Suspicion based on what?
> 
> I have a not yet finished patch that dumps the FDB :)
> 
> The contents change around a bit under the patch
> sets I have floating, but can certainly be determined
> when I have time to test things properly.

To be clear, if bit 9 is a "disable learning" bit, address learning is a
process that takes place on the ingress of a packet, and in this case
the ingress port is the CPU port. But the ndo_fdb_dump works with net
devices, of which CPU ports have none. So it seems unlikely that you
would see any difference in the output of "bridge fdb" that could be
attributed to that bit.

> > > Do we have some use for that feature in DSA taggers?
> >
> > Yes.
> 
> OK I'll add it to my TODO, right now trying to fix up the base
> of the RTL8366RB patch set to handle VLANs the right way.

But you didn't ask what that use is...