linux-kernel - Re: [PATCH V3 2/7] PM / OPP: Introduce "domain-performance-state" binding to OPP nodes

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Date:   Wed, 1 Mar 2017 17:13:22 -0600
From:   Rob Herring <robh@...nel.org>
To:     Rajendra Nayak <rnayak@...eaurora.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        "linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Lina Iyer <lina.iyer@...aro.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Jon Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH V3 2/7] PM / OPP: Introduce "domain-performance-state"
 binding to OPP nodes

On Wed, Mar 1, 2017 at 12:27 AM, Rajendra Nayak <rnayak@...eaurora.org> wrote:
>
>
> On 02/28/2017 09:22 PM, Rob Herring wrote:
>> On Tue, Feb 28, 2017 at 9:14 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>> [...]
>>>
>>>>>                                     ---> Parent domain-2 (Contains Perfomance states)
>>>>>                                     |
>>>>>                                     |
>>>>> C.) DeviceX  --->  Parent-domain-1  |
>>>>>                                     |
>>>>>                                     |
>>>>>                                     ---> Parent domain-3 (Contains Perfomance states)
>>>>
>>>> I'm a bit confused. How does a domain have 2 parent domains?
>>>
>>> This comes from the early design of the generic PM domain, thus I
>>> assume we have some HW with such complex PM topology. However, I don't
>>> know if it is actually being used.
>>>
>>> Moreover, the corresponding DT bindings for "power-domains" parents,
>>> can easily be extended to cover more than one parent. See more in
>>> Documentation/devicetree/bindings/power/power_domain.txt
>>
>> I could easily see device having 2 power domains. For example a cpu
>> may have separate domains for RAM/caches and logic. And nesting of
>
> yet the bindings for power-domains (for consumer devices) only allows for
> one powerdomain to be associated with a device.

There's nothing in the binding only allowing that. If that was true,
then #powerdomain-cells would be pointless as the property size would
tell you the number of cells. Now it may be that we simply don't have
any cases with more than 1. Hopefully that's not because bindings are
working around PM domain limitations/requirements.

Rob