netdev - Re: [PATCH] net: fec: Add support for multiple phys on mdiobus

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Date:	Mon, 21 Jan 2013 13:06:02 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Wolfgang Grandegger <wg@...ndegger.com>
Cc:	netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	shawn.guo@...aro.org, davem@...emloft.net
Subject: Re: [PATCH] net: fec: Add support for multiple phys on mdiobus

On Mon, Jan 21, 2013 at 12:07:30PM +0100, Wolfgang Grandegger wrote:
> On 01/21/2013 11:07 AM, Sascha Hauer wrote:
> > On Mon, Jan 21, 2013 at 09:56:24AM +0100, Wolfgang Grandegger wrote:
> >> On 01/21/2013 09:37 AM, Sascha Hauer wrote:
> >>> There may be multiple phys on an mdio bus. This series adds support
> >>> for this to the fec driver. I recently had a board which has a switch
> >>> connected to the fec's mdio bus, so I had to pick the correct phy.
> >>
> >> Pick one PHY from a switch port? Well, does a PHY-less (or fixed-link)
> >> configuration for a switch not make more sense?
> > 
> > Yes, you're probably right.
> > 
> >> Various ARM Ethernet
> >> contoller drivers do not support it. I recently needed a hack for an
> >> AT91 board.
> > 
> > I wonder how we want to proceed. Should there be a devicetree property
> > 'fixed-link' like done for fs_enet (and not recommended for new code,
> > stated in the comment above of_phy_connect_fixed_link)?
> 
> Also the gianfar and ucc_geth drivers use this interface (via fixed
> link phy). I tried to use it for the AT91 macb driver but stopped
> quickly because the usage was not straight forward (too much code)...
> even if the idea of using a fake fixed-link phy is not bad.
> 
> > Currently I have a property 'phy' in the fec binding which has a phandle
> > to a phy provided by the fec's mdio bus, but this could equally well
> 
> But than the cable must be connected to the associated switch port.
> 
> > point to a fixed dummy phy:
> > 
> > 	phy = &fixed-phy;
> 
> The link speed, full/half duplex and maybe some mroe parameter should
> be configurable via device tree.

Well this could be done when the fixed phy driver could be registered
with the devicetree, maybe like this:

	fixed-phy: mdiophy {
		compatible = "mdio-fixed-phy";
		link = "100FD";
	};

The good thing about this would be that every ethernet driver could just
use such a fixed phy, any external mdio phy (like on Marvell Armada) or
just a phy connected to the internal mdio interface provided by the ethernet
core.

I probably should write a RFC to devicetree-discuss.

Sascha


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