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Date:   Mon, 11 May 2020 20:34:04 -0700
From:   Florian Fainelli <>
To:     Vladimir Oltean <>,,
Subject: Re: [PATCH v2 net-next 08/15] net: dsa: sja1105: prepare tagger for
 handling DSA tags and VLAN simultaneously

On 5/11/2020 6:53 AM, Vladimir Oltean wrote:
> From: Vladimir Oltean <>
> In VLAN-unaware mode, sja1105 uses VLAN tags with a custom TPID of
> 0xdadb. While in the yet-to-be introduced best_effort_vlan_filtering
> mode, it needs to work with normal VLAN TPID values.
> A complication arises when we must transmit a VLAN-tagged packet to the
> switch when it's in VLAN-aware mode. We need to construct a packet with
> 2 VLAN tags, and the switch will use the outer header for routing and
> pop it on egress. But sadly, here the 2 hardware generations don't
> behave the same:
> - E/T switches won't pop an ETH_P_8021AD tag on egress, it seems
>   (packets will remain double-tagged).
> - P/Q/R/S switches will drop a packet with 2 ETH_P_8021Q tags (it looks
>   like it tries to prevent VLAN hopping).
> But looks like the reverse is also true:
> - E/T switches have no problem popping the outer tag from packets with
>   2 ETH_P_8021Q tags.
> - P/Q/R/S will have no problem popping a single tag even if that is
>   ETH_P_8021AD.
> So it is clear that if we want the hardware to work with dsa_8021q
> tagging in VLAN-aware mode, we need to send different TPIDs depending on
> revision. Keep that information in priv->info->qinq_tpid.
> The per-port tagger structure will hold an xmit_tpid value that depends
> not only upon the qinq_tpid, but also upon the VLAN awareness state
> itself (in case we must transmit using 0xdadb).
> Signed-off-by: Vladimir Oltean <>

Reviewed-by: Florian Fainelli <>

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