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

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Date:   Tue, 15 Nov 2016 10:56:45 -0800
From:   Stephen Boyd <sboyd@...eaurora.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rob Herring <robh@...nel.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 11/15, Viresh Kumar wrote:
> On 14-11-16, 18:13, Stephen Boyd wrote:
> > On 11/14, Rob Herring wrote:
> > > On Fri, Nov 11, 2016 at 08:41:20AM +0530, Viresh Kumar wrote:
> > > > On 10-11-16, 14:51, Stephen Boyd wrote:
> > > > > 
> > > > > 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.
> 
> Its not just PIA, but impossible AFAICT.
> 
> There are two important pieces of information we need for multiple
> regulator support:
> - Which regulator in the consumer node corresponds to which entry in
>   the OPP table. As Mark mentioned earlier, DT should be able to get
>   us this.

This is also possible from C code though. Or is there some case
where it isn't possible if we're sharing the same table with two
devices? I'm lost on when this would ever happen.

It feels like trying to keep the OPP table agnostic of the
consuming device and the device's binding is more trouble than
it's worth. Especially considering we have opp-shared and *-name
now.

> - The order in which the supplies need to be programmed. We have all
>   agreed to do this in code instead of inferring it from DT and this
>   patch series already does that.

Agreed. Encoding a sequence into DT doesn't sound very feasible.
How is this going to be handled though? I don't see any users of
the code we're reviewing here, so it's hard to grasp how things
will work. It would be really useful if we had some user of the
code included in the patch series to get the big picture.

> 
> I want to solve the first problem here and I don't see how it can be
> solved using such entries:
> 
> 	cpus {
> 		cpu@0 {
> 			compatible = "arm,cortex-a7";
> 			...
> 
>                         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";
> 		opp-shared;
> 
> 		opp@...0000000 {
> 			opp-hz = /bits/ 64 <1000000000>;
> 			opp-microvolt = <970000>, /* Supply 0 */
> 					<960000>, /* Supply 1 */
> 					<960000>; /* Supply 2 */
> 		};
>         };
> 
> The code can't figure out which of vcc0, vcc1, vcc2 is added first in
> the CPU node and so we need to get the order somehow. A separate
> binding as I mentioned earlier is a probably (ugly) solution.
> 
> > I think the problem is that Viresh wants the binding to be "self
> > describing" so that the OPP can be used without a driver knowing
> > that a supply corresponds to a particular column in the voltage
> > table.
> 
> Right, and that's what Mark suggested as well.
> 
> > I don't understand that though. Can't we set the supply
> > names from C code somewhere based on the consumer of the OPPs?
> 
> That's what this patch series is doing right now.
> 
> So, are you saying that the way this patchset does it is fine with you
> ?

That's just to handle the ordering of operations? I need to take
a minute and understand what's changing. You may have spent
plenty of time developing/updating, but I haven't spent near
enough time understanding what's going on in these patches to
give a thorough review.

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