netdev - Re: [PATCH net-next 15/15] net: mscc: ocelot: don't hardcode the number of the CPU port

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Date:   Sun, 10 Nov 2019 19:33:52 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Joergen Andreasen <joergen.andreasen@...rochip.com>,
        "Allan W. Nielsen" <allan.nielsen@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        netdev <netdev@...r.kernel.org>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next 15/15] net: mscc: ocelot: don't hardcode the
 number of the CPU port

On Sun, 10 Nov 2019 at 19:12, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Sun, Nov 10, 2019 at 07:00:33PM +0200, Vladimir Oltean wrote:
> > On Sun, 10 Nov 2019 at 18:50, Andrew Lunn <andrew@...n.ch> wrote:
> > >
> > > On Sat, Nov 09, 2019 at 03:03:01PM +0200, Vladimir Oltean wrote:
> > > > From: Vladimir Oltean <vladimir.oltean@....com>
> > > >
> > > > VSC7514 is a 10-port switch with 2 extra "CPU ports" (targets in the
> > > > queuing subsystem for terminating traffic locally).
> > >
> > > So maybe that answers my last question.
> > >
> > > > There are 2 issues with hardcoding the CPU port as #10:
> > > > - It is not clear which snippets of the code are configuring something
> > > >   for one of the CPU ports, and which snippets are just doing something
> > > >   related to the number of physical ports.
> > > > - Actually any physical port can act as a CPU port connected to an
> > > >   external CPU (in addition to the local CPU). This is called NPI mode
> > > >   (Node Processor Interface) and is the way that the 6-port VSC9959
> > > >   (Felix) switch is integrated inside NXP LS1028A (the "local management
> > > >   CPU" functionality is not used there).
> > >
> > > So i'm having trouble reading this and spotting the difference between
> > > the DSA concept of a CPU port and the two extra "CPU ports". Maybe
> > > using the concept of virtual ports would help?
> > >
> > > Are the physical ports number 0-9, and so port #10 is the first extra
> > > "CPU port", aka a virtual port? And so that would not work for DSA,
> > > where you need a physical port.
> > >
> > >       Andrew
> >
> > Right. See my other answer which links to Ocelot documentation.
>
> Yes, i'm getting the picture now.
>
> The basic problem is that in the Linux kernel CPU port has a specific
> meaning, and it is clashing with the meaning used in the datasheet. So
> maybe in the driver, we need to refer to these two ports as 'local
> ports'?
>

Hmm, I don't know. Both types of CPU ports lead to management CPUs,
but to different types of them. I understand the clash with the DSA
meaning, but even if I rename it I would have to provide an
explanation relative to the datasheet definitions (and I already
explain that the NPI mode is the DSA type of CPU port). I'm not sure
there is a net gain.

> The mv88e6xxx driver has a similar problem. Some of the switches have
> a Z80 embedded in them. And this Z80 has an ethernet interface
> connected to the switch core as port 12. So far we don't support it,
> but if we ever do, i'm sure we will end up calling it the z80 port,
> not the cpu port.
>
>     Andrew