netdev - Re: [PATCH net-next v8 3/5] net: dsa: add out-of-band tagging protocol

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Message-ID: <02d0cc2d-26b4-e655-c2b9-9514a29074f5@gmail.com>
Date:   Mon, 7 Nov 2022 10:40:13 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Vladimir Oltean <vladimir.oltean@....com>
Cc:     Maxime Chevallier <maxime.chevallier@...tlin.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "linux-arm-kernel@...ts.infradead.org\"" 
        <linux-arm-kernel@...ts.infradead.org>,
        Luka Perkov <luka.perkov@...tura.hr>,
        Robert Marko <robert.marko@...tura.hr>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>
Subject: Re: [PATCH net-next v8 3/5] net: dsa: add out-of-band tagging
 protocol

On 11/7/22 10:24, Jakub Kicinski wrote:

[snip]

> Yeah, it's a balancing act. Please explore the metadata option, I think
> most people jump to the skb extension because they don't know about
> metadata. If you still want skb extension after, I'll look away.

It seems to me like we are trying too hard to have a generic out of band 
solution to provide tagger information coming from a DMA descriptor as 
opposed to just introducing a DSA tagger variant specific to the format 
being used and specific to the switch + integrated MAC. Something like 
DSA_TAG_IPQDMA or whatever the name chosen would be, may be fine.

The only value I see at this point in just in telling me that the tagger 
format is coming from a DMA descriptor, but other than that, it is just 
a middle layer that requires marshalling of data on both sides, so sure 
the idea behind DSA was to be able to mix and match any Ethernet MAC 
with any discrete switch, but integrating both into the same ASIC does 
nullify the design goal.
-- 
Florian