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

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Date:   Mon, 23 Aug 2021 00:28:51 +0000
From:   Alvin Šipraga <ALSI@...g-olufsen.dk>
To:     Vladimir Oltean <olteanv@...il.com>
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 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.