netdev - Re: [RFC PATCH net-next 3/5] net: dsa: tag_rtl8

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Message-ID: <20210823003132.fdafjnci4y56cmnd@skbuf>
Date:   Mon, 23 Aug 2021 03:31:32 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Alvin Šipraga <ALSI@...g-olufsen.dk>
Cc:     Alvin Šipraga <alvin@...s.dk>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Michael Rasmussen <MIR@...g-olufsen.dk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH net-next 3/5] net: dsa: tag_rtl8_4: add realtek 8
 byte protocol 4 tag

On Mon, Aug 23, 2021 at 12:28:51AM +0000, Alvin Šipraga wrote:
> On 8/23/21 1:45 AM, Vladimir Oltean wrote:
> > On Sun, Aug 22, 2021 at 11:37:28PM +0000, Alvin Šipraga wrote:
> >>>>>> +	skb->offload_fwd_mark = 1;
> >>>>>
> >>>>> At the very least, please use
> >>>>>
> >>>>> 	dsa_default_offload_fwd_mark(skb);
> >>>>>
> >>>>> which does the right thing when the port is not offloading the bridge.
> >>>>
> >>>> Sure. Can you elaborate on what you mean by "at the very least"? Can it
> >>>> be improved even further?
> >>>
> >>> The elaboration is right below. skb->offload_fwd_mark should be set to
> >>> zero for packets that have been forwarded only to the host (like packets
> >>> that have hit a trapping rule). I guess the switch will denote this
> >>> piece of info through the REASON code.
> >>
> >> Yes, I think it will be communicated in REASON too. I haven't gotten to
> >> deciphering the contents of this field since it has not been needed so
> >> far: the ports are fully isolated and all bridging is done in software.
> >
> > In that case, setting skb->offload_fwd_mark to true is absolutely wrong,
> > since the bridge is told that no software forwarding should be done
> > between ports, as it was already done in hardware (see nbp_switchdev_allowed_egress).
> >
> > I wonder how this has ever worked? Are you completely sure that bridging
> > is done in software?
>
> You are absolutely right, and indeed I checked just now and the bridging
> is not working at all.
>
> Deleting the line (i.e. skb->offload_fwd_mark = 0) restores the expected
> bridging behaviour.
>
> Based on what you have said, do I understand correctly that
> offload_fwd_mark shouldn't be set until bridge hardware offloading has
> been implemented?
>
> Thanks for your detailed review so far.

So back to my initial suggestion:

| At the very least, please use
|
| 	dsa_default_offload_fwd_mark(skb);
|
| which does the right thing when the port is not offloading the bridge.

This way, you won't have to touch this code even after you start
implementing .port_bridge_join and .port_bridge_leave. It deals with
both cases.