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Date:   Sun, 24 May 2020 00:50:18 +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 23/05/2020 02:35, Anson Huang wrote:
> > 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.
> 
> Whatever the slope of the temperature increase?

Yes.

> 
> >> 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?
> 
> May be I misunderstood but only the change as below is needed. No need to
> add a trip point, especially an 'active' trip which is a for an active cooling
> device like a fan.
> 
> diff --git a/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> b/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> index cc7152ecedd9..bea263bd06b4 100644
> --- a/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> +++ b/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> @@ -231,10 +231,10 @@ cooling-maps {
>  				map0 {
>  					trip = <&cpu_alert0>;
>  					cooling-device =
> -						<&A53_0 THERMAL_NO_LIMIT
> THERMAL_NO_LIMIT>,
> -						<&A53_1 THERMAL_NO_LIMIT
> THERMAL_NO_LIMIT>,
> -						<&A53_2 THERMAL_NO_LIMIT
> THERMAL_NO_LIMIT>,
> -						<&A53_3 THERMAL_NO_LIMIT
> THERMAL_NO_LIMIT>;
> +						<&A53_0 2 2>,
> +						<&A53_1 2 2>,
> +						<&A53_2 2 2>,
> +						<&A53_3 2 2>
>  				};
>  			};
>  		};
> 
> 

Thanks, I will have a try to see if it meets our expectation.

Anson

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