netdev - Re: [PATCH net-next 4/6] arm64: dts: fsl: ls1028a: Add Felix switch port DT node

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Message-ID: <20190624152344.3bv46jjhhygo6zwl@lx-anielsen.microsemi.net>
Date:   Mon, 24 Jun 2019 17:23:45 +0200
From:   "Allan W. Nielsen" <allan.nielsen@...rochip.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        "David S . Miller" <davem@...emloft.net>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexandru Marginean <alexandru.marginean@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Allan Nielsen <Allan.Nielsen@...rosemi.com>,
        Rob Herring <robh+dt@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH net-next 4/6] arm64: dts: fsl: ls1028a: Add Felix switch
 port DT node

Hi Andrew,

The 06/24/2019 16:26, Andrew Lunn wrote:
> > > Yeah, there are 2 ethernet controller ports (managed by the enetc driver) 
> > > connected inside the SoC via SGMII links to 2 of the switch ports, one of
> > > these switch ports can be configured as CPU port (with follow-up patches).
> > > 
> > > This configuration may look prettier on DSA, but the main restriction here
> > > is that the entire functionality is provided by the ocelot driver which is a
> > > switchdev driver.  I don't think it would be a good idea to copy-paste code
> > > from ocelot to a separate dsa driver.
> > > 
> > 
> > We should probably make the ocelot driver a DSA driver then...
> An important part of DSA is being able to direct frames out specific
> ports when they ingress via the CPU port. Does the silicon support
> this? At the moment, i think it is using polled IO.

That is supported, it requires a bit of initial configuration of the Chip, but
nothing big (I believe this configuration is part of Claudiu's change-set).

But how do you envision this done?

- Let the existing SwitchDev driver and the DSA driver use a set of common
  functions.
- Convert the existing Ocelot driver from SwitchDev to DSA
- Fork (copy) the existing driver of Ocelot, and modify it as needed for the
  Felix driver

My guess is the first one, but I would like to understand what you have in mind.

BTW: The Ocelot switch does exist in an other (register compatible) version
without the MIPS CPU. That version would use a MAC-2-MAC connection to an
external CPU, and would fit the DSA model. And we have been considering how to
best represent that version in the kernel.

/Allan