Hi, Daniel

Subject: RE: [PATCH] thermal: imx8mm: Add get_trend ops

Hi, Daniel

quoted

Subject: Re: [PATCH] thermal: imx8mm: Add get_trend ops

On 23/05/2020 02:35, Anson Huang wrote:

quoted

Hi, Daniel

quoted

Subject: Re: [PATCH] thermal: imx8mm: Add get_trend ops

On 13/05/2020 04:58, Anson Huang wrote:

quoted

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.

quoted

quoted

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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.

quoted

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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.

quoted

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.

I tried modifying the min/max to '2' in cooling map, it works that whenever cooling
action is needed, the max cooling action will be applied. But I also noticed some behaviors
which NOT as expected:

1. to easy the test, I enable the " CONFIG_THERMAL_WRITABLE_TRIPS", and just modify the
passive trip threshold to trigger the cooling action, this is much more easy then putting the board
into an oven to increase the SoC temperature or running many high loading test to increase the temperature,
but when I modify the passive trip threshold to be lower than current temperature, the cooling action is NOT
triggered immediately, it is because the default step_wise governor will NOT trigger the cooling action when
the trend is THERMAL_TREND_STABLE.
But what expected is, when the temperature is exceed the passive trip threshold, the cooling action can be
triggered immediately no matter the trend is stable or raising. That means we have to implement our own
.get_trend callback?

2. No margin for releasing the cooling action, for example, if cooling action is triggered, when the temperature
drops below the passive trip threshold, the cooling action will be cancelled immediately, if SoC keeps running
at full performance, the temperature will increase very soon, which may cause the SoC keep triggering/cancelling
the cooling action around the passive trip threshold. If there is a margin, the situation will be much better.

Do you have any idea/comment about them?

Thanks,
Anson
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