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

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Date:	Mon, 21 Jan 2013 12:33:04 +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 01/21/2013 12:12 PM, Florian Fainelli wrote:
> On 01/21/2013 12:07 PM, 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.
>>
>>> 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.
> 
> Is not what of_phy_connect_fixed_link() offer? I am not sure there can
> be much done by an helper than that.

Probably. I now remember that my primary problem with the AT91 board was
that it does not have yet device tree support.

Wolfgang.

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