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

From: Wolfgang Grandegger <[email-masked]>
Date: Mon, 21 Jan 2013 12:07:30 +0100

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.

> Currently there seems to be no common convention for the devicetree how
> to handle such situations, or am I missing something?

That's also may impression. There seem to be a few more related hacks:

$ find . -name '*.c'| xargs grep -i "phy-less" 
./ethernet/amd/au1000_eth.c:			netdev_info(dev, "using PHY-less setup\n");
./ethernet/amd/au1000_eth.c:	} else { /* PHY-less op, assume full-duplex */
./ethernet/ibm/emac/core.c:	/* PHY-less configuration.
./ethernet/ibm/emac/core.c:		/* PHY-less configuration.

I would prefer to handle the "fixed-link" property of the ethernet dt
node directly in the driver with a generic helper function.

Wolfgang.