netdev - Re: net: dsa: Realtek switch drivers

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Date: Wed, 3 Jul 2024 14:39:22 +1200
From: Chris Packham <chris.packham@...iedtelesis.co.nz>
To: Andrew Lunn <andrew@...n.ch>
Cc: Luiz Angelo Daros de Luca <luizluca@...il.com>,
 Linus Walleij <linus.walleij@...aro.org>,
 "alsi@...g-olufsen.dk" <alsi@...g-olufsen.dk>,
 Florian Fainelli <f.fainelli@...il.com>,
 "olteanv@...il.com" <olteanv@...il.com>, Marek Behún
 <kabel@...nel.org>, "ericwouds@...il.com" <ericwouds@...il.com>,
 David Miller <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 "kuba@...nel.org" <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 "justinstitt@...gle.com" <justinstitt@...gle.com>,
 "rmk+kernel@...linux.org.uk" <rmk+kernel@...linux.org.uk>,
 netdev <netdev@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "sander@...nheule.net" <sander@...nheule.net>
Subject: Re: net: dsa: Realtek switch drivers


On 2/07/24 14:50, Andrew Lunn wrote:
>> What would I be loosing if I don't use the DSA infrastructure? I got kind of
>> hung up at the point where it really wanted a CPU port and I just couldn't
>> provide a nice discrete NIC.
>   
> DSA gives you a wrapper which handles some common stuff, which you
> will end up implementing if you do a pure switchdev driver. Mostly
> translating netdev to port index. The tagging part of DSA does not
> apply if you have DMA per user port, so you don't loose anything
> there.  I guess you cannot cascade multiple switches, so the D in DSA
> also does not apply. You do lose out on tcpdump support, since you
> don't have a conduit interface which all traffic goes through.
>
> But you should not try to impose DSA if it does not fit. There are
> 'simple' pure switchdev drivers, you don't need to try to understand
> the mellanox code. Look at the microchip drivers for something to
> copy.
One reason for using DSAI've just found is that in theory the RTL930x 
supports a CPU disabled mode where you do connect it to an external CPU 
and the data travels over SGMII like you'd get with a traditional DSA 
design. It's not a mode I'm planning on supporting anytime soon but it 
might come up when I get round to submitting some patches.