linux-kernel - Re: [PATCH] Fix mt7622.dtsi thermal cpu

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Date:   Wed, 23 Jun 2021 20:43:15 +0200
From:   Eric Woudstra <ericwouds@...il.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
CC:     Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix mt7622.dtsi thermal cpu


I choose "hot" before, because 87 degrees seems ok to start frequency throttling. But, yes, it should be passive.

87 is still quite low if I compare this temperature with the wrt3200acm Marvell dual core arm soc. They even went above 100 degrees so I feel for an arm processor inside a router box it is fine to use 87 degrees But maybe someone at Mediatek can give some more details about operating temperatures.

It may be possible to leave the active map in the device tree as some users of the bananapi might choose to install a fan as it is one of the options.

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On Jun 23, 2021, 5:58 PM, at 5:58 PM, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>On 23/06/2021 17:35, Eric Woudstra wrote:
>> It is only useful to set 1 map with the regulated temperature for cpu
>> frequency throttling. Same as in the kernel document example.
>> 
>> 
>> It has no use to set frequency scaling on 2 different temperature
>> trip points, as the lowest one makes sure the higher one(s) are never
>> reached.
>
>I looked more closely the DT and there is a misunderstanding of the
>thermal framework in the definition.
>
>There is one trip point with the passive type and the cpu cooling
>device, followed by a second trip point with the active type *but* the
>same cpu cooling device. That is wrong.
>
>And finally, there is the hot trip point as a third mapping and the
>same
>cooling device.
>
>The hot trip point is only there to notify userspace and let it take an
>immediate action to prevent an emergency shutdown when reaching the
>critical temperature.
>
>> It can be applied only at 1 trip point. Multiple trip points
>> is only usefully for fan control to make sure the fan is not too
>> noisy when it is not necessary to be noisy.
>> 
>> 
>> The CPU will almost come to a dead stop when it starts to pass the
>> lowest thermal map with frequency throttling.
>> 
>> This is why it is a bug and needs a fix, not only adjustment.
>
>Yes, you are right. It should be something like (verbatim copy):
>
>diff --git a/arch/arm64/boot/dts/mediatek/mt7622.dtsi
>b/arch/arm64/boot/dts/mediatek/mt7622.dtsi
>index 890a942ec608..88c81d24f4ff 100644
>--- a/arch/arm64/boot/dts/mediatek/mt7622.dtsi
>+++ b/arch/arm64/boot/dts/mediatek/mt7622.dtsi
>@@ -136,24 +136,18 @@ secmon_reserved: secmon@...00000 {
>
> 	thermal-zones {
> 		cpu_thermal: cpu-thermal {
>-			polling-delay-passive = <1000>;
>+			polling-delay-passive = <250>;
> 			polling-delay = <1000>;
>
> 			thermal-sensors = <&thermal 0>;
>
> 			trips {
> 				cpu_passive: cpu-passive {
>-					temperature = <47000>;
>+					temperature = <77000>;
> 					hysteresis = <2000>;
> 					type = "passive";
> 				};
>
>-				cpu_active: cpu-active {
>-					temperature = <67000>;
>-					hysteresis = <2000>;
>-					type = "active";
>-				};
>-
> 				cpu_hot: cpu-hot {
> 					temperature = <87000>;
> 					hysteresis = <2000>;
>@@ -173,18 +167,6 @@ map0 {
> 					cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> 							 <&cpu1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
> 				};
>-
>-				map1 {
>-					trip = <&cpu_active>;
>-					cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
>-							 <&cpu1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
>-				};
>-
>-				map2 {
>-					trip = <&cpu_hot>;
>-					cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
>-							 <&cpu1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
>-				};
> 			};
> 		};
> 	};
>
>
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