netdev - Re: [RFC net-next 2/2] net: dsa: tag_mtk: handle VLAN tag insertion on TX

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Date:   Thu, 26 Aug 2021 17:13:26 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     DENG Qingfang <dqfext@...il.com>
Cc:     Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC net-next 2/2] net: dsa: tag_mtk: handle VLAN tag insertion
 on TX

On Thu, Aug 26, 2021 at 01:29:56PM +0800, DENG Qingfang wrote:
> On Thu, Aug 26, 2021 at 03:03:49AM +0300, Vladimir Oltean wrote:
> > 
> > You cannot just remove the old code. Only things like 8021q uppers will
> > send packets with the VLAN in the hwaccel area.
> > 
> > If you have an application that puts the VLAN in the actual AF_PACKET
> > payload, like:
> > 
> > https://github.com/vladimiroltean/tsn-scripts/blob/master/isochron/send.c
> > 
> > then you need to handle the VLAN being in the skb payload.
> 
> I've actually tested this (only apply patch 2 without .features) and it
> still worked.
> 
> The comment says the VLAN tag need to be combined with the special tag in
> order to perform VLAN table lookup,

It does say this.

> so we can set its destination port vector to all zeroes and the switch
> will forward it like a data frame (TX forward offload),

And it does not say this. So this is supported after all with mt7530?
Are you looking to add support for that?

> but as we allow multiple bridges which are either VLAN-unaware or
> VLAN-aware with the same VID, there is no way to determine the
> destination bridge unless we maintain some VLAN translation mapping.

What does "VLAN translation mapping" mean, practically?
Other drivers which cannot remap VIDs to internal VLANs just restrict a
single VLAN-aware bridge, and potentially multiple VLAN-unaware ones.