linux-kernel - Re: [PATCH v2 1/3] dt-binding: power: Add otg regulator binding

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Message-ID: <CAL_Jsq+w0ide6kkwCgQPxZ6dbL0MrSEBxe6XnjcsECP9_zRV7g@mail.gmail.com>
Date:	Thu, 10 Dec 2015 09:18:23 -0600
From:	Rob Herring <robh@...nel.org>
To:	Bjorn Andersson <bjorn.andersson@...ymobile.com>
Cc:	"Bird, Tim" <Tim.Bird@...ymobile.com>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"sre@...nel.org" <sre@...nel.org>,
	"dbaryshkov@...il.com" <dbaryshkov@...il.com>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"agross@...eaurora.org" <agross@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tbird20d@...il.com" <tbird20d@...il.com>,
	"Cavin, Courtney" <Courtney.Cavin@...ymobile.com>
Subject: Re: [PATCH v2 1/3] dt-binding: power: Add otg regulator binding

On Wed, Dec 9, 2015 at 3:08 PM, Rob Herring <robh@...nel.org> wrote:
> On Wed, Dec 9, 2015 at 1:59 PM, Bjorn Andersson
> <bjorn.andersson@...ymobile.com> wrote:
>> On Wed 09 Dec 06:36 PST 2015, Rob Herring wrote:
>>
>>> On Wed, Dec 9, 2015 at 6:55 AM, Tim Bird <tim.bird@...ymobile.com> wrote:
>>> > On 12/08/2015 08:11 PM, Rob Herring wrote:
>>> >> On Tue, Dec 08, 2015 at 04:40:16PM -0800, Tim Bird wrote:
>>> >>> Add a binding for the regulator which controls the OTG chargepath switch.
>>> >>> The OTG switch gets its power from pm8941_5vs1, and that should be
>>> >>> expressed as a usb-otg-in-supply property in the DT node for the
>>> >>> charger driver.  The regulator name is "otg".
>>>
>>> [...]
>>>
>>> >>> +child nodes:
>>> >>> +- otg:
>>> >>> +  Usage: optional
>>> >>> +  Description: This node defines a regulator used to control the direction
>>> >>> +               of VBUS voltage - specifically: whether to supply voltage
>>> >>> +               to VBUS for host mode operation of the OTG port, or allow
>>> >>> +               input voltage from external VBUS for charging.  In the
>>> >>> +               hardware, the supply for this regulator comes from
>>> >>> +               usb-otg-in-supply.
>>> >>
>>> >> Doesn't this regulator need to have a name defined?
>>> >
>>> > I'm not sure what you mean.  The regulator name is "otg", defined by the DT node
>>> > name. The code requires that the DT node name be "otg", and defines a regulator
>>> > with the same name.
>>> >
>>> > As far as I know, you have to define a DT label for the node, in order
>>> > to reference this regulator with a phandle.  Is that what you are referring to?
>>> > I usually use "chg_otg" as the label.  Are you asking that this be reflected
>>> > in the example?
>>>
>>> You need a regulator-name property. Also, should should define valid
>>> values for regulator-min-microvolt and regulator-max-microvolt.
>>>
>>
>> The regulator has a name, derived from the node name, and this is
>> significant. If the developer wants an additional human readable name
>> for some reason they can use the optional regulator-name property.
>>
>> The regulator is a simple switch and as such inherits voltage properties
>> from its supply. It should therefor not have any specified voltage
>> range.
>>
>>> Thinking about this some more, the node name should be generic, so
>>> just "regulator". The label does not need to be generic.
>>>
>>
>> The name of the node is significant, as it's used for matching the
>> regulator to an implementation.
>
> Ah yes, you are right. I forget what an oddball the regulator binding is.
>
> And if voltage switches don't need min and max properties, then it is
> fine as is. Still, the empty node with no properties seems odd to me.

Thinking some more about this, what bothers me is just having "otg
{};" gives no clue as to what the node is for w/o the documentation.
"otg" alone could mean several things. I think minimally, it needs
either a node name that gives some indication it is a regulator or
Vbus supply, a required regulator-name or even a comment.

Rob
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