linux-kernel - Re: [PATCH v3 6/7] dt-bindings: soc: qcom: Extend RPMh power controller binding to describe thermal warming device

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Message-ID: <CAL_Jsq+OoyC5FZxYrX_KN1QLDXRvKuFbH=9pLiELsOtoPixnPA@mail.gmail.com>
Date:   Tue, 29 Oct 2019 15:16:11 -0500
From:   Rob Herring <robh@...nel.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Thara Gopinath <thara.gopinath@...aro.org>,
        Eduardo Valentin <edubezval@...il.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Amit Kucheria <amit.kucheria@...durent.com>,
        Mark Rutland <mark.rutland@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 6/7] dt-bindings: soc: qcom: Extend RPMh power
 controller binding to describe thermal warming device

On Tue, Oct 29, 2019 at 5:07 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Tue, 29 Oct 2019 at 02:36, Rob Herring <robh@...nel.org> wrote:
> >
> > On Thu, Oct 17, 2019 at 12:10:15PM -0400, Thara Gopinath wrote:
> > > On 10/17/2019 11:43 AM, Ulf Hansson wrote:
> > > > On Thu, 17 Oct 2019 at 17:28, Thara Gopinath <thara.gopinath@...aro.org> wrote:
> > > >>
> > > >> Hello Ulf,
> > > >> Thanks for the review!
> > > >>
> > > >> On 10/17/2019 05:04 AM, Ulf Hansson wrote:
> > > >>> On Wed, 16 Oct 2019 at 21:37, Thara Gopinath <thara.gopinath@...aro.org> wrote:
> > > >>>>
> > > >>>> RPMh power controller hosts mx domain that can be used as thermal
> > > >>>> warming device. Add a sub-node to specify this.
> > > >>>>
> > > >>>> Signed-off-by: Thara Gopinath <thara.gopinath@...aro.org>
> > > >>>> ---
> > > >>>>  Documentation/devicetree/bindings/power/qcom,rpmpd.txt | 10 ++++++++++
> > > >>>>  1 file changed, 10 insertions(+)
> > > >>>>
> > > >>>> diff --git a/Documentation/devicetree/bindings/power/qcom,rpmpd.txt b/Documentation/devicetree/bindings/power/qcom,rpmpd.txt
> > > >>>> index eb35b22..fff695d 100644
> > > >>>> --- a/Documentation/devicetree/bindings/power/qcom,rpmpd.txt
> > > >>>> +++ b/Documentation/devicetree/bindings/power/qcom,rpmpd.txt
> > > >>>> @@ -18,6 +18,16 @@ Required Properties:
> > > >>>>  Refer to <dt-bindings/power/qcom-rpmpd.h> for the level values for
> > > >>>>  various OPPs for different platforms as well as Power domain indexes
> > > >>>>
> > > >>>> += SUBNODES
> > > >>>> +RPMh alsp hosts power domains that can behave as thermal warming device.
> > > >>>> +These are expressed as subnodes of the RPMh. The name of the node is used
> > > >>>> +to identify the power domain and must therefor be "mx".
> > > >>>> +
> > > >>>> +- #cooling-cells:
> > > >>>> +       Usage: optional
> > > >>>> +       Value type: <u32>
> > > >>>> +       Definition: must be 2
> > > >>>> +
> > > >>>
> > > >>> Just wanted to express a minor thought about this. In general we use
> > > >>> subnodes of PM domain providers to represent the topology of PM
> > > >>> domains (subdomains), this is something different, which I guess is
> > > >>> fine.
> > > >>>
> > > >>> I assume the #cooling-cells is here tells us this is not a PM domain
> > > >>> provider, but a "cooling device provider"?
> > > >> Yep.
> > > >>>
> > > >>> Also, I wonder if it would be fine to specify "power-domains" here,
> > > >>> rather than using "name" as I think that is kind of awkward!?
> > > >> Do you mean "power-domain-names" ? I am using this to match against the
> > > >> genpd names defined in the provider driver.
> > > >
> > > > No. If you are using "power-domains" it means that you allow to
> > > > describe the specifier for the provider.
> > > Yep. But won't this look funny in DT ? The provider node will have a sub
> > > node with a power domain referencing to itself Like below: Is this ok ?
> > >
> > > rpmhpd: power-controller {
> > >                                 compatible = "qcom,sdm845-rpmhpd";
> > >                                 #power-domain-cells = <1>;
> > >
> > >                       ...
> > >                       ...
> > >                               mx_cdev: mx {
> > >                                         #cooling-cells = <2>;
> > >                                         power-domains = <&rpmhpd      SDM845_MX>;
> > >                                 };
> > >
> >
> > The whole concept here seems all wrong to me. Isn't it what's in the
> > power domain that's the cooling device. A CPU power domain is not a
> > cooling device, the CPU is. Or we wouldn't make a clock a cooling
> > device, but what the clock drives.
>
> Well, I don't think that's entirely correct description either.
>
> As I see it, it's really the actual PM domain (that manages voltages
> for a power island), that needs to stay in full power state and
> increase its voltage level, as to warm up some of the silicon. It's
> not a regular device, but more a characteristics of how the PM domain
> can be used.

First I've heard of Si needing warming...

I think I'd just expect the power domain provider to know which
domains to power on then.

Rob