linux-kernel - Re: [RFC 1/2] dt-bindings: thermal: sprd: Add virtual thermal documentation

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Message-ID: <1af5220c-f598-58f4-488e-fdd505477ed5@linaro.org>
Date:   Fri, 27 Nov 2020 14:26:07 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>, gao.yunxiao6@...il.com,
        rui.zhang@...el.com, amitk@...nel.org, robh+dt@...nel.org,
        javi.merino@...nel.org
Cc:     linux-pm@...r.kernel.org, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        orsonzhai@...il.com, zhang.lyra@...il.com,
        "jeson.gao" <jeson.gao@...soc.com>
Subject: Re: [RFC 1/2] dt-bindings: thermal: sprd: Add virtual thermal
 documentation

Hi Lukasz,

On 27/11/2020 10:27, Lukasz Luba wrote:
> 
> 
> On 11/27/20 8:35 AM, gao.yunxiao6@...il.com wrote:
>> From: "jeson.gao" <jeson.gao@...soc.com>
>>
>> virtual thermal node definition description in dts file
>>
>> Signed-off-by: jeson.gao <jeson.gao@...soc.com>
>> ---

[ ... ]

> It's coming back. There were attempts to solve this problem.
> Javi tried to solved this using hierarchical thermal zones [1].
> It was even agreed (IIRC during LPC) but couldn't continue. Then Eduardo
> was going to continue this (last message at [3]). Unfortunately,
> development stopped.
> 
> I also have out-of-tree similar implementation for my Odroid-xu4,
> which does no have an 'SoC' sensor, but have CPU sensors and needs
> some aggregation function to get temperature.
> 
> I can pick up Javi's patches and continue 'hierarchical thermal zones'
> approach.
> 
> Javi, Daniel, Rui what do you think?

I already worked on the hierarchical thermal zones and my opinion is
that fits not really well.

We want to define a new feature because the thermal framework is built
on the 1:1 relationship between a governor and a thermal zone.

Practically speaking, we want to mitigate two thermal zones from one
governor, especially here the IPA governor.

The DTPM framework is being implemented to solve that by providing an
automatic power rebalancing between the power manageable capable devices.

In our case, the IPA would stick on the 'sustainable-power' resulting on
the aggregation of the two performance domains and set the power limit
on the parent node. The automatic power rebalancing will ensure maximum
throughput between the two performance domains instead of capping the whole.

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