linux-kernel - RE: [PATCH net-next 09/10] net: renesas: rswitch: add simple l3 routing

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Message-ID:
 <TY4PR01MB14282A958BD280F500143A32882C9A@TY4PR01MB14282.jpnprd01.prod.outlook.com>
Date: Mon, 17 Nov 2025 10:46:25 +0000
From: Michael Dege <michael.dege@...esas.com>
To: Andrew Lunn <andrew@...n.ch>
CC: Nikita Yushchenko <nikita.yoush@...entembedded.com>, Yoshihiro Shimoda
	<yoshihiro.shimoda.uh@...esas.com>, Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Richard
 Cochran <richardcochran@...il.com>, niklas.soderlund
	<niklas.soderlund@...natech.se>, Paul Barker <paul@...rker.dev>, Rob Herring
	<robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
	<conor+dt@...nel.org>, Geert Uytterhoeven <geert+renesas@...der.be>,
	magnus.damm <magnus.damm@...il.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-renesas-soc@...r.kernel.org"
	<linux-renesas-soc@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, Christophe JAILLET
	<christophe.jaillet@...adoo.fr>
Subject: RE: [PATCH net-next 09/10] net: renesas: rswitch: add simple l3
 routing

> -----Original Message-----
> From: Andrew Lunn <andrew@...n.ch>
> Sent: Friday, November 7, 2025 2:47 PM
> To: Michael Dege <michael.dege@...esas.com>
> Cc: Nikita Yushchenko <nikita.yoush@...entembedded.com>; Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@...esas.com>; Andrew Lunn <andrew+netdev@...n.ch>; David S. Miller
> <davem@...emloft.net>; Eric Dumazet <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>; Paolo
> Abeni <pabeni@...hat.com>; Richard Cochran <richardcochran@...il.com>; niklas.soderlund
> <niklas.soderlund@...natech.se>; Paul Barker <paul@...rker.dev>; Rob Herring <robh@...nel.org>;
> Krzysztof Kozlowski <krzk+dt@...nel.org>; Conor Dooley <conor+dt@...nel.org>; Geert Uytterhoeven
> <geert+renesas@...der.be>; magnus.damm <magnus.damm@...il.com>; netdev@...r.kernel.org; linux-renesas-
> soc@...r.kernel.org; linux-kernel@...r.kernel.org; devicetree@...r.kernel.org; Christophe JAILLET
> <christophe.jaillet@...adoo.fr>
> Subject: Re: [PATCH net-next 09/10] net: renesas: rswitch: add simple l3 routing
>
> > > But, there is a more interesting question about this patchset (that
> > > actually stopped me from submitting it when it was originally
> > > developed).
> > >
> > > What do people thing about the entire approach used to detect streams to offload?
> > >
> > > The situation is:
> > > - hardware is capable of doing L3 routing, with some (limited)
> > > packet update capabilities - rewrite DST MAC, decrease TTL,
> > > - there is interest to use that, because software L3 routing even at
> > > 1Gbps consumes significant CPU load, and for 5Gbps will likely not
> > > keep the speed at all (we did not have hw to try),
> > > - but - given the capabilities of hw are incomparably weaker than
> > > capabilities of linux networking, which approach to take to detect streams for offloading?
> > >
> > > Second question - how exactly to get the routing decision from the
> > > kernel stack, to apply it in hardware? I was not able to find any existing implementations of
> something similar...
>
> You should probably look at how the mellanox switch does this. It is kind of the reference
> implementation. The sparx5 and prestera might have something, i don't remember their capabilities.
>
> Some of the mediatek devices also do interesting things with flows, but that is more for NAT, not
> necessarily L3 routing.

Thank you for your valuable input. I will take a closer look at the mentioned drivers and reimplement
that part of the driver. I am currently busy with a different feature. Therefore, I will start over
once I am done.

Michael

>
>       Andrew
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