linux-kernel - RE: [PATCH net] net: renesas: rswitch: fix forwarding offload statemachine

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Message-ID:
 <TY4PR01MB142823B7BBDE92603467F6AE88266A@TY4PR01MB14282.jpnprd01.prod.outlook.com>
Date: Fri, 6 Feb 2026 05:54:17 +0000
From: Michael Dege <michael.dege@...esas.com>
To: 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>
CC: "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>, Christian
 Mardmoeller <christian.mardmoeller@...esas.com>, Dennis Ostermann
	<dennis.ostermann@...esas.com>
Subject: RE: [PATCH net] net: renesas: rswitch: fix forwarding offload
 statemachine

Hello Nikita,

I am sorry I missed this latest message of yours.

> -----Original Message-----
> From: Nikita Yushchenko <nikita.yoush@...entembedded.com>
> Sent: Thursday, February 5, 2026 4:04 PM
> To: Michael Dege <michael.dege@...esas.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>
> Cc: netdev@...r.kernel.org; linux-renesas-soc@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH net] net: renesas: rswitch: fix forwarding offload statemachine
> 
> >>> The driver was originally designed to enable hardware forwarding
> >>> when not less than two ports are in forwarding state. When only one port has hw forwarding, there
> is no destination to forward.
> >>>
> >>> Nikita
> >>>
> >>
> >> The current driver allows Linux to use the bridge port as local port
> >> to the bridge. The offloading Also supports switching traffic to
> >> Linux through the bridge port. Therefore, the offloading shouldn't Be dropped if only one external
> port is up on the bridge.
> >
> > "Offloading" means - forward a frame from one hw port to other hw port
> > without inserting it into CPU queue. Offloaded frame is never visible to software bridge.
> >
> > There is code that allows offload only if the linux bridge device used
> > to connect rswitch ports does not have anything else.  If it has
> > something else, offloading is disabled (because there is no way to know when a frame can be
> processed within rswitch hw without sending it to cpu).
> 
> Ah I see the code that explicitly enabled l2 offload only when at least two ports are active is not in
> mainline.
> 
> Still, l2 offload requires at least two ports participating, by definition.
> When there is only one port with hw forwarding enabled, it will get empty allowed forward destination
> mask.

Yes, that is right, but there are still two HW ports involved in the HW forwarding. The remaining TSN 
port and the GWCA as internal port. Therefore, it is OK from the HW viewpoint.

Best regards,

Michael