netdev - Re: [PATCH net-next v2 2/5] net: microchip: sparx5: Adding more tc flower keys for the IS2 VCAP

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Date:   Thu, 3 Nov 2022 17:21:57 +0100
From:   Steen Hegelund <steen.hegelund@...rochip.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Casper Andersson <casper.casan@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        <UNGLinuxDriver@...rochip.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        "Wan Jiabing" <wanjiabing@...o.com>,
        Nathan Huckleberry <nhuck@...gle.com>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Daniel Machon <daniel.machon@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH net-next v2 2/5] net: microchip: sparx5: Adding more tc
 flower keys for the IS2 VCAP

Hi Jacub,

On Wed, 2022-11-02 at 18:28 -0700, Jakub Kicinski wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
> content is safe
> 
> On Wed, 2 Nov 2022 14:11:37 +0100 Steen Hegelund wrote:
> > I have sent a version 4 of the series, but I realized after sending it, that
> > I
> > was probably not understanding the implications of what you were saying
> > entirely.
> > 
> > As far as I understand it now, I need to have a matchall rule that does a
> > goto
> > from chain 0 (as this is where all traffic processing starts) to my first
> > IS2
> > VCAP chain and this rule activates the IS2 VCAP lookup.
> > 
> > Each of the rules in this VCAP chain need to point to the next chain etc.
> > 
> > If the matchall rule is deleted the IS2 VCAP lookups should be disabled as
> > there
> > is no longer any way to reach the VCAP chains.
> > 
> > Does that sound OK?
> 
> It does as far as I understand.
> 
> I haven't grasped what the purpose of using multiple chains is in
> case of your design. IIRC correctly other drivers use it for instance
> to partition TCAMs with each chain having a different set of fields it
> can match on. But I don't see templates used in sparx5.

Yes, so far I have only added the IS2 VCAP, but there are 3 more that I am
planning to to add, and they have very different capabilities in terms of keys
and actions, so I think it makes good sense to keep them in separate chains.

> 
> In general in TC offloads you can reject any configuration you can't
> (or choose not to) support, and make up your own constraints (e.g. only
> specific priority or chain values are supported).

Understood.

> 
> But for a "target" ruleset, i.e. ruleset comprised fully of rules you
> do offload - the behavior of executing that ruleset in software and in
> the device must be the same.
> 
> Dunno if that helps :)

It does, thanks!

I been fireing up a QEMU instance so I have been able to test my understanding,
and it looks like I now have the same experience when I test the same rule there
and in the hardware of Sparx5.

BR
Steen