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Date:   Tue, 8 Nov 2022 10:20:44 +0100
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Subject: Re: [PATCH 08/14] net: vlan: remove invalid VLAN protocol warning
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To:     Vladimir Oltean <olteanv@gmail.com>
Cc:     netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, linux-kernel@vger.kernel.org
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 <3b275dda-39ac-282d-8a46-d3a95fdfc766@nbd.name>
 <20221108090039.imamht5iyh2bbbnl@skbuf>
From:   Felix Fietkau <nbd@nbd.name>
In-Reply-To: <20221108090039.imamht5iyh2bbbnl@skbuf>
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On 08.11.22 10:00, Vladimir Oltean wrote:
> On Tue, Nov 08, 2022 at 07:08:46AM +0100, Felix Fietkau wrote:
>> On 07.11.22 22:57, Vladimir Oltean wrote:
>> > Aren't you calling __vlan_hwaccel_put_tag() with the wrong thing (i.e.
>> > htons(RX_DMA_VPID()) as opposed to VPID translated to something
>> > digestible by the rest of the network stack.. ETH_P_8021Q, ETH_P_8021AD
>> > etc)?
>> 
>> The MTK ethernet hardware treats the DSA special tag as a VLAN tag and
>> reports it as such. The ethernet driver passes this on as a hwaccel tag, and
>> the MTK DSA tag parser consumes it. The only thing that's sitting in the
>> middle looking at the tag is the VLAN device lookup with that warning.
>> 
>> Whenever DSA is not being used, the MTK ethernet device can also process
>> regular VLAN tags. For those tags, htons(RX_DMA_VPID()) will contain the
>> correct VPID.
> 
> So I don't object to the overall theme of having the DSA master offload
> the parsing and removal of the DSA tag, but you knock down a bit too
> many fences if you carry the DSA tag in skb->vlan_present (not only VLAN
> upper device lookup, but also the flow dissector).
> 
> What other information will be present in the offloaded DSA headers
> except source port information? Maxime Chevallier is also working on a
> similar problem for qca8k, except in that case, the RX DSA offload seems
> to not be optional for him.
> 
> https://patchwork.kernel.org/project/netdevbpf/patch/20221104174151.439008-4-maxime.chevallier@bootlin.com/
> 
> Would a solution based on METADATA_HW_PORT_MUX and dst_metadata that
> point to refcounted, preallocated structs work for Mediatek SoCs with
> DSA, or would more information be necessary?
> 
> Meaning: mtk_eth_soc attaches the dst_metadata to the skb, tag_mtk.c
> retrieves and removes it.
I need to look into how METADATA_HW_PORT_MUX works, but I think it could 
work.

- Felix