netdev - Re: [PATCH] net: dsa: tag_brcm: legacy: fix daisy-chained switches

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Date:   Fri, 17 Mar 2023 17:40:30 +0100
From:   Álvaro Fernández Rojas <noltari@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     f.fainelli@...il.com, jonas.gorski@...il.com, olteanv@...il.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: tag_brcm: legacy: fix daisy-chained switches

El vie, 17 mar 2023 a las 17:32, Andrew Lunn (<andrew@...n.ch>) escribió:
>
> On Fri, Mar 17, 2023 at 01:08:15PM +0100, Álvaro Fernández Rojas wrote:
> > When BCM63xx internal switches are connected to switches with a 4-byte
> > Broadcom tag, it does not identify the packet as VLAN tagged, so it adds one
> > based on its PVID (which is likely 0).
> > Right now, the packet is received by the BCM63xx internal switch and the 6-byte
> > tag is properly processed. The next step would to decode the corresponding
> > 4-byte tag. However, the internal switch adds an invalid VLAN tag after the
> > 6-byte tag and the 4-byte tag handling fails.
> > In order to fix this we need to remove the invalid VLAN tag after the 6-byte
> > tag before passing it to the 4-byte tag decoding.
>
> Is there an errata for this invalid VLAN tag? Or is the driver simply
> missing some configuration for it to produce a valid VLAN tag?

Yes, this is a HW issue due to the fact that Broadcom Legacy switches
which use a 6-byte tag cannot identify the tag of newer Broadcom
switches using a 4-byte tag and therefore adding their own tag along
with a default VLAN tag ignoring the corresponding untag bit in those
ports.
But Florian and Jonas can probably provide more information about this
HW issue, and also this link too:
https://github.com/openwrt/openwrt/issues/10313

>
> The description does not convince me you are fixing the correct
> problem.

Well, if you think that I should fix the configuration then I'm afraid
you're wrong.

>
>         Andrew

--
Álvaro