Re: [PATCH net] net: dsa: mt7530: don't change PVC_EG_TAG when CPU port becomes VLAN-aware

From: "Arınç ÜNAL" <arinc.unal@arinc9.com>
To: Vladimir Oltean <vladimir.oltean@nxp.com>, netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Sean Wang <sean.wang@mediatek.com>,
	Landen Chao <Landen.Chao@mediatek.com>,
	DENG Qingfang <dqfext@gmail.com>, Andrew Lunn <andrew@lunn.ch>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	AngeloGioacchino Del Regno 
	<angelogioacchino.delregno@collabora.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org,
	Frank Wunderlich <frank-w@public-files.de>,
	erkin.bozoglu@xeront.com, richard@routerhints.com
Subject: Re: [PATCH net] net: dsa: mt7530: don't change PVC_EG_TAG when CPU port becomes VLAN-aware
Date: Sun, 5 Feb 2023 22:25:27 +0300	[thread overview]
Message-ID: <3649b6f9-a028-8eaf-ac89-c4d0fce412da@arinc9.com> (raw)
In-Reply-To: <20230205140713.1609281-1-vladimir.oltean@nxp.com>

On 5.02.2023 17:07, Vladimir Oltean wrote:
> Frank reports that in a mt7530 setup where some ports are standalone and
> some are in a VLAN-aware bridge, 8021q uppers of the standalone ports
> lose their VLAN tag on xmit, as seen by the link partner.
> 
> This seems to occur because once the other ports join the VLAN-aware
> bridge, mt7530_port_vlan_filtering() also calls
> mt7530_port_set_vlan_aware(ds, cpu_dp->index), and this affects the way
> that the switch processes the traffic of the standalone port.
> 
> Relevant is the PVC_EG_TAG bit. The MT7530 documentation says about it:
> 
> EG_TAG: Incoming Port Egress Tag VLAN Attribution
> 0: disabled (system default)
> 1: consistent (keep the original ingress tag attribute)
> 
> My interpretation is that this setting applies on the ingress port, and
> "disabled" is basically the normal behavior, where the egress tag format
> of the packet (tagged or untagged) is decided by the VLAN table
> (MT7530_VLAN_EGRESS_UNTAG or MT7530_VLAN_EGRESS_TAG).
> 
> But there is also an option of overriding the system default behavior,
> and for the egress tagging format of packets to be decided not by the
> VLAN table, but simply by copying the ingress tag format (if ingress was
> tagged, egress is tagged; if ingress was untagged, egress is untagged;
> aka "consistent). This is useful in 2 scenarios:
> 
> - VLAN-unaware bridge ports will always encounter a miss in the VLAN
>    table. They should forward a packet as-is, though. So we use
>    "consistent" there. See commit e045124e9399 ("net: dsa: mt7530: fix
>    tagged frames pass-through in VLAN-unaware mode").
> 
> - Traffic injected from the CPU port. The operating system is in god
>    mode; if it wants a packet to exit as VLAN-tagged, it sends it as
>    VLAN-tagged. Otherwise it sends it as VLAN-untagged*.
> 
> *This is true only if we don't consider the bridge TX forwarding offload
> feature, which mt7530 doesn't support.
> 
> So for now, make the CPU port always stay in "consistent" mode to allow
> software VLANs to be forwarded to their egress ports with the VLAN tag
> intact, and not stripped.
> 
> Link: https://lore.kernel.org/netdev/trinity-e6294d28-636c-4c40-bb8b-b523521b00be-1674233135062@3c-app-gmx-bs36/
> Fixes: e045124e9399 ("net: dsa: mt7530: fix tagged frames pass-through in VLAN-unaware mode")
> Reported-by: Frank Wunderlich <frank-w@public-files.de>
> Tested-by: Frank Wunderlich <frank-w@public-files.de>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Tested on MT7621AT and MT7623NI boards with MT7530 switch. Both had this 
issue and this patch fixes it.

Tested-by: Arınç ÜNAL <arinc.unal@arinc9.com>

Unrelated to this, as in it existed before this patch, port@0 hasn't 
been working at all on my MT7621AT Unielec U7621-06 board and MT7623NI 
Bananapi BPI-R2.

Packets are sent out from master eth1 fine, the computer receives them. 
Frames are received on eth1 but nothing shows on the DSA slave interface 
of port@0. Sounds like malformed frames are received on eth1.

Cheers.
Arınç