linux-kernel - Re: [PATCH V3 1/9] PM / OPP: Reword binding supporting multiple regulators per device

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Date:   Mon, 14 Nov 2016 19:59:52 -0600
From:   Rob Herring <robh@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Stephen Boyd <sboyd@...eaurora.org>,
        Mark Brown <broonie@...nel.org>,
        Rafael Wysocki <rjw@...ysocki.net>, nm@...com,
        Viresh Kumar <vireshk@...nel.org>,
        linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>, d-gerlach@...com,
        devicetree@...r.kernel.org
Subject: Re: [PATCH V3 1/9] PM / OPP: Reword binding supporting multiple
 regulators per device

On Fri, Nov 11, 2016 at 08:41:20AM +0530, Viresh Kumar wrote:
> On 10-11-16, 14:51, Stephen Boyd wrote:
> > On 11/10, Viresh Kumar wrote:
> > > On 10-11-16, 16:36, Mark Brown wrote:
> > > > On Thu, Nov 10, 2016 at 09:34:40AM +0530, Viresh Kumar wrote:
> > > > > On 09-11-16, 14:58, Mark Brown wrote:
> > > > > > On Wed, Oct 26, 2016 at 12:02:56PM +0530, Viresh Kumar wrote:
> > > > 
> > > > > > > +  Entries for multiple regulators shall be provided in the same field separated
> > > > > > > +  by angular brackets <>. The OPP binding doesn't provide any provisions to
> > > > > > > +  relate the values to their power supplies or the order in which the supplies
> > > > > > > +  need to be configured.
> > > > 
> > > > > > I don't understand how this works.  If we have an unordered list of
> > > > > > values to set for regulators how will we make sense of them?
> > > > 
> > > > > The platform driver is responsible to identify the order and pass it on to the
> > > > > OPP core. And the platform driver needs to have that hard coded.
> > > > 
> > > > That *really* should be in the binding.
> > > 
> > > Okay, how do you suggest doing that? Will a property like supply-names
> > > in the OPP table be fine? Like this:
> > > 
> > > @@ -369,13 +378,16 @@ Example 4: Handling multiple regulators
> > >                         compatible = "arm,cortex-a7";
> > >                         ...
> > >  
> > > -                       cpu-supply = <&cpu_supply0>, <&cpu_supply1>, <&cpu_supply2>;
> > > +                       vcc0-supply = <&cpu_supply0>;
> > > +                       vcc1-supply = <&cpu_supply1>;
> > > +                       vcc2-supply = <&cpu_supply2>;
> > >                         operating-points-v2 = <&cpu0_opp_table>;
> > >                 };
> > >         };
> > >  
> > >         cpu0_opp_table: opp_table0 {
> > >                 compatible = "operating-points-v2";
> > > +               supply-names = "vcc0", "vcc1", "vcc2";
> > >                 opp-shared;
> > > 
> > 
> > No. The supply names (and also clock names/index) should be left
> > up to the consumer of the OPP table. We don't want to encode any
> > sort of details like this between the OPP table and the consumer
> > of it in DT because then it seriously couples the OPP table to
> > the consumer device. "The binding" in this case that needs to be
> > updated is the consumer binding, to indicate that it correlated
> > foo-supply and bar-supply to index 0 and 1 of the OPP table
> > voltages.
> 
> Are you saying that we shall have a property like this then?
> 
> diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
> index ee91cbdd95ee..733946df2fb8 100644
> --- a/Documentation/devicetree/bindings/opp/opp.txt
> +++ b/Documentation/devicetree/bindings/opp/opp.txt
> @@ -389,7 +389,10 @@ Example 4: Handling multiple regulators
>                         compatible = "arm,cortex-a7";
>                         ...
>  
> -                       cpu-supply = <&cpu_supply0>, <&cpu_supply1>, <&cpu_supply2>;
> +                       vcc0-supply = <&cpu_supply0>;
> +                       vcc1-supply = <&cpu_supply1>;
> +                       vcc2-supply = <&cpu_supply2>;
> +                       opp-supply-names = "vcc0", "vcc1", "vcc2";

Uh, no. You already have the names in the *-supply properties. Yes, they 
are a PIA to retrieve compared to a *-names property, but that is the 
nature of this style of binding.

Rob