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: <20210721094155.aoikj4ghf2d3a4ap@skbuf>
Date:   Wed, 21 Jul 2021 09:41:56 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Kurt Kanzenbach <kurt@...utronix.de>
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

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.