netdev - Re: [PATCH v2 net 1/2] net: dsa: sja1105: always enable the INCL

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Date: Tue, 27 Jun 2023 17:06:24 +0200
From: Simon Horman <simon.horman@...igine.com>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net 1/2] net: dsa: sja1105: always enable the
 INCL_SRCPT option

On Tue, Jun 27, 2023 at 12:42:06PM +0300, Vladimir Oltean wrote:
> Link-local traffic on bridged SJA1105 ports is sometimes tagged by the
> hardware with source port information (when the port is under a VLAN
> aware bridge).
> 
> The tag_8021q source port identification has become more loose
> ("imprecise") and will report a plausible rather than exact bridge port,
> when under a bridge (be it VLAN-aware or VLAN-unaware). But link-local
> traffic always needs to know the precise source port.
> 
> Modify the driver logic (and therefore: the tagging protocol itself) to
> always include the source port information with link-local packets,
> regardless of whether the port is standalone, under a VLAN-aware or
> VLAN-unaware bridge. This makes it possible for the tagging driver to
> give priority to that information over the tag_8021q VLAN header.
> 
> The big drawback with INCL_SRCPT is that it makes it impossible to
> distinguish between an original MAC DA of 01:80:C2:XX:YY:ZZ and
> 01:80:C2:AA:BB:ZZ, because the tagger just patches MAC DA bytes 3 and 4
> with zeroes. Only if PTP RX timestamping is enabled, the switch will
> generate a META follow-up frame containing the RX timestamp and the
> original bytes 3 and 4 of the MAC DA. Those will be used to patch up the
> original packet. Nonetheless, in the absence of PTP RX timestamping, we
> have to live with this limitation, since it is more important to have
> the more precise source port information for link-local traffic.
> 
> Fixes: d7f9787a763f ("net: dsa: tag_8021q: add support for imprecise RX based on the VBID")
> Fixes: 91495f21fcec ("net: dsa: tag_8021q: replace the SVL bridging with VLAN-unaware IVL bridging")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Simon Horman <simon.horman@...igine.com>