netdev - Re: [PATCH net-next 10/11] net: dsa: tag_8021q: manage RX VLANs dynamically at bridge join/leave time

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Message-ID: <87fsw8vtnr.fsf@kurt>
Date:   Wed, 21 Jul 2021 12:38:16 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>
Subject: Re: [PATCH net-next 10/11] net: dsa: tag_8021q: manage RX VLANs
 dynamically at bridge join/leave time

On Wed Jul 21 2021, Vladimir Oltean wrote:
> Hi Kurt,
>
> On Wed, Jul 21, 2021 at 11:06:58AM +0200, Kurt Kanzenbach wrote:
>> Hi Vladimir,
>> 
>> On Mon Jul 19 2021, Vladimir Oltean wrote:
>> > This is not to say that the reason for the change in this patch is to
>> > satisfy the hellcreek and similar use cases, that is merely a nice side
>> > effect.
>> 
>> Is it possible to use tag_8021q for port separation use cases now? I'd
>> be interested in it if that results in a simplified hellcreek
>> implementation :).
>
> Yes, but I still don't think it is worth it.
>
> At the moment, if I'm not mistaken, hellcreek reserves 3 VLANs or so,
> from 4093 to 4095. Whereas tag_8021q will reserve the entire range from
> 1024 to 3071. The VLAN IDs used by tag_8021q have a bitwise meaning of
> their own, so that range cannot be simply shifted (at least not easily).
>
> If you only want to use tag_8021q for port separation in standalone
> mode, and not really as a tagging protocol (tag_hellcreek.c will not see
> the tag_8021q VLANs), I suppose that restriction can be lifted somewhat:
> (a) tag_8021q can only reserve RX VLANs but not TX VLANs (that would
>     reduce the reserved range from 1024-3071 to 1024-2047)
> (b) tag_8021q can only reserve RX VLANs for the actual ds->num_ports and
>     ds->index values in use (which would further reduce the range to
>     1024-1026 in your case)
>
> In terms of driver implementation, not a lot would go away. The current
> places where you handle events, like hellcreek_setup_vlan_membership(),
> will still remain the way they are, but they will just set up a VLAN
> provided by tag_8021q instead of one provided by hellcreek_private_vid().
>
> Six of one, half a dozen of the other.

OK. Seems like it's not worth it.

Thanks,
Kurt

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