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From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Subject: Re: Fixed PHY Device Tree usage?
Date: Wed, 10 Jul 2013 18:22:16 +0200
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To: Florian Fainelli <florian@openwrt.org>
Cc: netdev <netdev@vger.kernel.org>, Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>, Gregory =?UTF-8?B?Q2zDqW1lbnQ=?= <gregory.clement@free-electrons.com>, Ezequiel Garcia <ezequiel.garcia@free-electrons.com>, Lior Amsalem <alior@marvell.com>, devicetree-discuss@lists.ozlabs.org, grant.likely@secretlab.ca, afleming@freescale.com
List-Id: devicetree@vger.kernel.org

Dear Florian Fainelli,

On Tue, 09 Jul 2013 19:02:05 +0100, Florian Fainelli wrote:

> > > We have a case of an hardware platform that uses the mvneta network
> > > driver, but instead of the SoC being connected to a PHY, it's connected
> > > directly to a switch, so my understanding is that there's no MDIO bus,
> > > and we should have a kind of a "fake PHY" to make the mvneta driver
> > > believe that the link is up, at a given speed.
> > 
> > Good timing, I was about to post questions/suggestions about how we
> > should represent fixed PHYs in device tree.

Great.

> > Well, it does not seem to be too far from the "hardware" reality to
> > describe a link between a switch CPU port and an Ethernet MAC as a
> > fixed PHY because that is what it really is in fact. Once you have a
> > drivers for your switch you can start using this PHY along with its
> > corresponding driver.

Ok.

> > There is a helper: of_phy_connect_fixed_link() in drivers/of/of_mdio.c
> > is flagged as being a
> > temporary solution for Freescale Ethernet drivers to move to something else,
> > so I would like to discuss what the "something else should be".

Yeah, I saw this helper function as well, and the comment you spotted.

> > Here what I would like to see the new "fixed-link" phy node look like:
> > 
> > ethernet-phy@0 {
> >      reg = <0>;
> >      id = "deadbeef";
> >      speed = <1000>;
> >      full-duplex;
> >      pause;
> >      asym-pause;
> > };
> > 
> > It has the same properties as the binding described in:
> > Documentation/devicetree/bindings/net/fsl-tsec-phy.txt but expressed in a
> > more explicit way instead of using an array of integers.

And so the fixed-phy driver would look for what exactly in the Device
Tree to find which fixed PHYs to create?

Should we have something like:

	mdio-fixed {
		compatible = "generic,mdio-fixed";
		phy0: ethernet-phy@0 {
			... all the properties you listed ...
			... maybe the "id" property is not needed
			    because of the phandle ...
		};

		phy1: ethernet-phy@1 {
			... all the properties you listed ...
			... maybe the "id" property is not needed
			    because of the phandle ...
		};
	};

	soc {
		ethernet@0 {
			phy = <&phy0>;
			...
		};

		ethernet@1 {
			phy = <&phy1>;
			...
		};
	};

or do you have in mind another representation?

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com