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Date:   Sat, 23 May 2020 14:33:40 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Anson Huang <anson.huang@....com>,
        "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

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?

>> 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>
 				};
 			};
 		};


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


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