Re: [PATCH net] net: dsa: Treat VLAN ID 0 as PVID untagged

[Vladimir Oltean]

Hi Florian,

On Wed, 12 Feb 2020 at 22:06, Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:
>
> VLAN ID 0 is special by all kinds and is really meant to be the default
> ingress and egress untagged VLAN. We were not configuring it that way
> and so we would be ingress untagged but egress tagged.
>
> When our devices are interfaced with other link partners such as switch
> devices, the results would be entirely equipment dependent. Some
> switches are completely fine with accepting an egress tagged frame with
> VLAN ID 0 and would send their responses untagged, so everything works,
> but other devices are not so tolerant and would typically reject a VLAN
> ID 0 tagged frame.

Are you sure that it's not in fact those devices that are not doing
what they're supposed to? VID 0 should be sent as tagged and no port
membership checks should be enforced on it.

>
> Fixes: 061f6a505ac3 ("net: dsa: Add ndo_vlan_rx_{add, kill}_vid implementation")
> Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> ---
> Hi all,
>
> After looking at all DSA drivers and how they implement port_vlan_add()
> I think this is the right change to do, but would appreciate if you
> could test this on your respective platforms to ensure this is not
> problematic.

I'm pretty sure this is problematic, for the simple reason that with
this change, DSA is insisting that the default PVID is 0, contrary to
the bridge core which insists it is 1. And some switches, like the
Microchip Ocelot/Felix, don't support more than 1 egress-untagged
VLAN, so adding one of the VIDs 0 or 1 will fail (I don't know the
exact order off-hand). See 1c44ce560b4d ("net: mscc: ocelot: fix
vlan_filtering when enslaving to bridge before link is up") for more
details of how that is going to work.

>
> Thank you
>
>
>  net/dsa/slave.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 088c886e609e..d3a2782eb94d 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -1100,6 +1100,7 @@ static int dsa_slave_vlan_rx_add_vid(struct net_device *dev, __be16 proto,
>  {
>         struct dsa_port *dp = dsa_slave_to_port(dev);
>         struct bridge_vlan_info info;
> +       u16 flags = 0;
>         int ret;
>
>         /* Check for a possible bridge VLAN entry now since there is no
> @@ -1118,7 +1119,13 @@ static int dsa_slave_vlan_rx_add_vid(struct net_device *dev, __be16 proto,
>                         return -EBUSY;
>         }
>
> -       ret = dsa_port_vid_add(dp, vid, 0);
> +       /* VLAN ID 0 is special and should be the default egress and ingress
> +        * untagged VLAN, make sure it gets programmed as such.
> +        */
> +       if (vid == 0)
> +               flags = BRIDGE_VLAN_INFO_PVID | BRIDGE_VLAN_INFO_UNTAGGED;

IEEE 802.1Q-2018, page 247, Table 9-2âReserved VID values:

The null VID. Indicates that the tag header contains only priority
information; no VID is
present in the frame. This VID value shall not be configured as a PVID
or a member of a VID
Set, or configured in any FDB entry, or used in any Management operation.

> +
> +       ret = dsa_port_vid_add(dp, vid, flags);
>         if (ret)
>                 return ret;
>
> --
> 2.17.1
>

Is this a test?

Regards,
-Vladimir