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

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Date:   Tue, 28 Feb 2017 20:13:40 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Rob Herring <robh@...nel.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>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH V3 2/7] PM / OPP: Introduce "domain-performance-state"
 binding to OPP nodes

Hi Rob,

On Tue, Feb 28, 2017 at 4:52 PM, Rob Herring <robh@...nel.org> 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
> power domains is certainly common, but a power domain being contained
> in 2 different parents? I don't even see how that is possible in the
> physical design. Now if we're mixing PM and power domains again and
> the cpu device is pointing to the cpu PM domain which contains 2 power
> domains, then certainly that is possible.

One of them could be a power area, the other a clock domain.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds