linux-kernel - RE: [PATCH] thermal: imx8mm: Add get

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Date:   Sat, 23 May 2020 00:35:10 +0000
From:   Anson Huang <anson.huang@....com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        "rui.zhang@...el.com" <rui.zhang@...el.com>,
        "amit.kucheria@...durent.com" <amit.kucheria@...durent.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] thermal: imx8mm: Add get_trend ops

Hi, Daniel

> Subject: Re: [PATCH] thermal: imx8mm: Add get_trend ops
> 
> On 13/05/2020 04:58, Anson Huang wrote:
> > Add get_trend ops for i.MX8MM thermal to apply fast cooling mechanism,
> > when temperature exceeds passive trip point, the highest cooling
> > action will be applied, and when temperature drops to lower than the
> > margin below passive trip point, the lowest cooling action will be
> > applied.
> 
> You are not describing what is the goal of this change.

The goal of this change is to make sure whenever temperature exceeds passive trip point,
the highest cooling action will be applied immediately, e.g., if there are many cpufreq OPP,
the default cooling will be step by step, it will take some more rounds to make cpufreq drop
to lowest OPP, while on i.MX, we expect the cpufreq drop to lowest OPP immediately.

> 
> IIUC, the resulting change will be an on/off action. The thermal zone is
> mitigated with the highest cooling effect, so the lowest OPP, then the
> temperature trend is stable until it goes below the trip - margin where the
> mitigation is stopped.

Yes, your understanding is correctly, once the temperature exceeds passive trip point,
the highest cooling action will be applied immediately and then it will be stable there
until temperature drop to trip - margin, then the cooling action will be cancelled, the
margin is to avoid the back and forth near the passive trip point.

> 
> Except, I'm missing something, setting a trip point with a 10000 hysteresis and
> a cooling map min/max set to the highest opp will result on the same.

Yes setting cooling map min/max cooling state to highest OPP will make the highest
cooling action applied immediately, and to have the function of cooling action being
cancelled when temperature drops to trip - margin, I have to define another trip point,
say passive trip point is 85000, and cooling map min/max set to highest OPP in passive
trip point then add another trip point named "active" with 75000, and without any
cooling map in it, right?

If yes, then I think I can try to make the changes in DT instead of thermal driver. 

Thanks,
Anson