Re: [PATCH net-next v2 3/4] net: dsa: initial MT7628 tagging driver

[Andrew Lunn <andrew@lunn.ch>]

On Mon, Mar 30, 2026 at 09:40:16PM +0300, Joris Vaisvila wrote:
> Add support for the MT7628 embedded switch's tag.
> 
> The MT7628 tag is merged with the VLAN TPID field when a VLAN is
> appended by the switch hardware. It is not installed if the VLAN tag is
> already there on ingress. Due to this hardware quirk the tag cannot be
> trusted for port 0 if we don't know that the VLAN was added by the
> hardware. As a workaround for this the switch is configured to always
> append the port PVID tag even if the incoming packet is already tagged.
> The tagging driver can then trust that the tag is always accurate and
> the whole VLAN tag can be removed on ingress as it's only metadata for
> the tagger.
> 
> On egress the MT7628 tag allows precise TX, but the correct VLAN tag
> from tag_8021q is still appended or the switch will not forward the
> packet.
> 
> Signed-off-by: Joris Vaisvila <joey@tinyisr.com>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew