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Subject: Re: [PATCH v3 6/7] dt-bindings: soc: qcom: Extend RPMh power
 controller binding to describe thermal warming device
To:     Rob Herring <robh@kernel.org>, Ulf Hansson <ulf.hansson@linaro.org>
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Cc:     Eduardo Valentin <edubezval@gmail.com>,
        Zhang Rui <rui.zhang@intel.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Andy Gross <agross@kernel.org>,
        Amit Kucheria <amit.kucheria@verdurent.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Linux PM <linux-pm@vger.kernel.org>,
        DTML <devicetree@vger.kernel.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
From:   Thara Gopinath <thara.gopinath@linaro.org>
Message-ID: <5DB99DDE.3090308@linaro.org>
Date:   Wed, 30 Oct 2019 10:27:42 -0400
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Hi Rob,

Thanks for the review.

On 10/29/2019 04:16 PM, Rob Herring wrote:
> On Tue, Oct 29, 2019 at 5:07 AM Ulf Hansson <ulf.hansson@linaro.org> wrote:
>>
>> On Tue, 29 Oct 2019 at 02:36, Rob Herring <robh@kernel.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@linaro.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@linaro.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@linaro.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...
Cold regions and non-closing of circuits is what I am told.
> 
> I think I'd just expect the power domain provider to know which
> domains to power on then.
I will just retain #cooling-cells in the power domain provider and let
the driver identify the actual power domains.

> 
> Rob
> 


-- 
Warm Regards
Thara