netdev - Re: Fixed PHY Device Tree usage?

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Date:	Fri, 12 Jul 2013 13:05:59 +0100
From:	Florian Fainelli <florian@...nwrt.org>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Gregory Clément 
	<gregory.clement@...e-electrons.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"grant.likely" <grant.likely@...retlab.ca>, afleming@...escale.com
Subject: Re: Fixed PHY Device Tree usage?

Hello Thomas,

2013/7/12 Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>:

>> Why not? Since we are already have to scan the entire MDIO bus we are
>> attached to, when we encounter such a PHY node with the special
>> "fixed" properties, we just call fixed_phy_add() with the right
>> parameters and voila. Which is also the reason why I was suggesting to
>> put the "fixed" PHY nodes as sub-nodes of the real MDIO node such that
>> we have this logic only in one place.
>
> I'm still not sure to understand you here. Scanning the *entire* DT
> tree and consider all nodes having a property named "fixed" as fixed
> PHYs is definitely not acceptable. So I suppose you have a different
> idea, but I'm still not getting it. Where in the DT would the fixed PHY
> driver start looking for fixed PHYs ?

I am talking about scanning the MDIO bus DT nodes, not the entire DT.
That job is already done by of_mdiobus_probe() to register PHY
devices, so having a central point where the knowledge of how to treat
PHY deivces could be here I guess.

>
>> > So that's really what I was asking: how is the fixed PHY driver going
>> > to know which DT nodes to look at. Is it a platform_driver, where the
>> > corresponding DT node has sub-nodes? Is it something else? Or a
>> > specific compatible string?
>>
>> Without DT at play here, the usual way to register a fixed PHY is:
>>
>> 1) make your arch code or whatever runs before the fixed MDIO bus
>> probing to call fixed_phy_add() with the expected parameters
>> 2) when your ethernet driver probes its PHY devices, format the phy
>> name to be bound to the fixed bus with the expected address by then
>> the fixed MDIO bus would have already been probed and would find the
>> fixed PHY nodes because of the first step
>> 3) call of_phy_connect() from your driver to attach to the fixed PHY
>
> Right, but that's still doesn't answer the question of how the fixed
> PHY driver discovers from the DT which PHYs to instantiate.
>
> For example, we would probably have something:
>
>         phys {
>                 phy0: phy@0 {
>                         ... PHY properties ...
>                 };
>                 phy1: phy@1 {
>                         ... PHY properties ...
>                 };
>         };
>
>         soc {
>                 ethernet@0 {
>                         compatible = "...";
>                         ...
>                         phy = <&phy0>;
>                 };
>                 ethernet@1 {
>                         compatible = "...";
>                         ...
>                         phy = <&phy1>;
>                 };
>         };
>
> How will the fixed PHY driver know that it should instantiate
> phy@0 and phy@1 as PHY devices?

Well either we go with some specific compatible property like
"ethernet-phy-fixed" for instance, or we simply add a boolean property
to the node, so a fixed PHY would either look like this:

phy {
         compatible = "linux,ethernet-phy-fixed";
         speed = <1000>;
         duplex = <1>;
         pause;
         asym-pause;
};

or respectively, something like this:

phy {
         fixed;
         speed = <1000>;
         duplex = <1>;
         pause;
         asym-pause;
};
--
Florian
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