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

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Date:	Tue, 22 Jan 2013 16:03:04 +0100
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Florian Fainelli <florian@...nwrt.org>
CC:	Sascha Hauer <s.hauer@...gutronix.de>, 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 01/22/2013 03:47 PM, Florian Fainelli wrote:
> On 01/22/2013 08:22 AM, Wolfgang Grandegger wrote:
>>> 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";
>>>     };
>>
>> I find that confusing. There is *no* phy but just a fixed link to the
>> switch...
>>
>>> 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.
>>
>> What is wrong with the existing "fixed-link" property of the *ethernet*
>> node. The fixed-link handling should/could be done in the phy layer, and
>> not in the driver as it currently is implemented. Maybe that's the
>> reason why the current code is regarded as hack!
> 
> As far as I have used it with the CPMAC driver, the fixed PHY is a
> specific PHY device and there is no specific handling to be done by the
> Ethernet MAC driver but eventually changing its MII bus id so that it is
> named "fixed-0" to allow the fixed PHY driver to bind. Put differently,

There is special handling for the fixed link, e.g. here:

http://lxr.linux.no/#linux+v3.7.4/drivers/net/ethernet/freescale/gianfar.c#L1462

This could be hidden in the PHY layer allowing all ethernet drivers
using the "fixed-link" property.

> using the fixed PHY driver is a kind of "last" resort thing to cope with
> situations like:
> 
> - switch not providing a consistent PHY-like interface on the MDC/MDIO bus
> - switches not connected to the MDC/MDIO bus of the Ethernet MAC they
> forward to
> 
> What exactly do you mean by "as it currently is implemented"? that you
> do not like?

As Sascha pointed out, the implementation is labeled as "hack", which
should be fixed sooner than later. It's just not clear why ;).

Wolfgang.

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