linux-kernel - Re: [PATCH v3 5/6] ARM: dts: omap: update usb_otg

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Date:	Thu, 21 Mar 2013 11:10:07 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	kishon <kishon@...com>
CC:	balbi@...com, gregkh@...uxfoundation.org, arnd@...db.de,
	akpm@...ux-foundation.org, rob@...dley.net, davem@...emloft.net,
	cesarb@...arb.net, linux-usb@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
	tony@...mide.com, grant.likely@...retlab.ca,
	rob.herring@...xeda.com, b-cousson@...com, linux@....linux.org.uk,
	eballetbo@...il.com, javier@...hile0.org, mchehab@...hat.com,
	santosh.shilimkar@...com, broonie@...nsource.wolfsonmicro.com,
	swarren@...dia.com, linux-doc@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 5/6] ARM: dts: omap: update usb_otg_hs data

On 03/21/2013 12:23 AM, kishon wrote:
> Hi,
> 
> On Thursday 21 March 2013 02:29 AM, Stephen Warren wrote:
>> On 03/20/2013 03:12 AM, Kishon Vijay Abraham I wrote:
>>> Updated the usb_otg_hs dt data to include the *phy* and *phy-names*
>>> binding in order for the driver to use the new generic PHY framework.
>>> Also updated the Documentation to include the binding information.
>>
>>> diff --git a/Documentation/devicetree/bindings/usb/omap-usb.txt
>>> b/Documentation/devicetree/bindings/usb/omap-usb.txt
>>> index abce256..3d6f9f6 100644
>>> --- a/Documentation/devicetree/bindings/usb/omap-usb.txt
>>> +++ b/Documentation/devicetree/bindings/usb/omap-usb.txt
>>> @@ -19,6 +19,9 @@ OMAP MUSB GLUE
>>>    - power : Should be "50". This signifies the controller can supply
>>> upto
>>>      100mA when operating in host mode.
>>>    - usb-phy : the phandle for the PHY device
>>> + - phy : the phandle for the PHY device (used by generic PHY framework)
>>> + - phy-names : the names of the PHY corresponding to the PHYs
>>> present in the
>>> +   *phy* phandle.
>>
>> If the intent is for those properties to be generic and used by any DT
>> binding that refers to a PHY node, I think you'd want to define those
>> properties in e.g. Documentation/devicetree/bindings/phy/phy.txt, just
>> like common clock/GPIO/... properties are defined in standalone common
>> files.
> 
> Ok. Will add it.
>>
>> I think you want to require that DT nodes that represent PHYs have a
>> #phy-cells property, and that the format of the phy property be
>> <&phy_phandle phy_specifier*>, where #phy-cells in the referenced node
>> defines how many cells are part of phy_specifier*, just like (almost)
>> any other DT property that references another node by phandle. That way,
>> if a single DT node represents a HW block that implements e.g. 3 PHYs,
>> it can use #phy-cells = <1>, and the referencing phy property can
>> include a cell that indicates which of those 3 PHYs is being referenced.
> 
> Currently, if a single phandle have reference to multiple PHYs, we can
> get PHY by passing index or by name as give in phy-names.
> I'm not sure if we have <&phy_phandle phy_specifier*>, what could that
> phy_specifier be? Maybe phy_type?

I'm not talking about the case where a consumer node references multiple
PHYs. As you say, that is indeed handled by the driver looking at a
particular index in the phys property, or using phy-names.

I'm talking about the case where a single provider provides multiple
PHYs. For example, consider:

phys: phy {
    compatible = "xxx";
    reg = <...>;
    #phy-cells = <1>;
};

That node describes an IP block that implements 3 different PHYs. The
registers are inter-mixed in such a way that you can't split it into 3
separate nodes each with a separate device instance. If the consumers
simply say:

phys = <&phys>;

then which of the 3 PHYs are you referring to?

Instead, the consumer needs to say one of:

phys = <&phys 0>;
phys = <&phys 1>;
phys = <&phys 2>;

in order to specify which of the PHYs it refers to.

The number of cells in the phy property after the phandle is specified
by the #phy-cells property in the node referred to by the phandle. The
meaning of all those cells is defined by the binding for the phy node.
This could include both the PHY ID (as in my example here), or whatever
configuration information or flags the provider needs. For example, both
GPIOs and interrupts have specifiers than describe both of these things.

For more background, take a look at almost any other binding that uses
phandles.

By the way, the property in the consumer should probably be "phys" not
"phy" to be consistent with other similar properties (e.g. gpios,
interrupts, ... which are all plural).
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