linux-kernel - Re: [PATCH net] net: dsa: b53: fix untagged traffic sent via cpu tagged with VID 0

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Message-ID: <20250605203331.twof2p2orvuxwuzt@skbuf>
Date: Thu, 5 Jun 2025 23:33:31 +0300
From: Vladimir Oltean <olteanv@...il.com>
To: Jonas Gorski <jonas.gorski@...il.com>
Cc: Florian Fainelli <florian.fainelli@...adcom.com>,
	Andrew Lunn <andrew@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: b53: fix untagged traffic sent via cpu
 tagged with VID 0

On Thu, Jun 05, 2025 at 11:20:43PM +0300, Vladimir Oltean wrote:
> Testing both on sja1105, as well as on veth using software bridging, the
> answer should be "tagged with VID 2". However, you make it sounds like
> the answer on b53 is "untagged".

Sorry, some neurons misfired. I don't expect the b53 answer to be
anything other than "tagged with VID 2". The bridge passes the skb as
tagged with VID 2 already.

Only if the bridge port VLAN 2 were egress-untagged, would the skb be
coming to ndo_start_xmit() as VLAN-untagged. Then it would be processed
in VID 2 in software, and in VID 0 in hardware. But the fact that VID 2
is egress-untagged in software just like VID 0 is egress-untagged in
hardware will mask that. That would only potentially matter for source
address learning, which I'm not sure whether it exists on CPU-injected
packets on b53.