Thread (19 messages) 19 messages, 4 authors, 2021-06-25

Re: [PATCH] Fix mt7622.dtsi thermal cpu

From: Eric Woudstra <hidden>
Date: 2021-06-24 13:29:45
Also in: linux-arm-kernel, linux-devicetree, lkml 

The SOC runs unthrotlled slowly to 80 degrees. This takes minutes. Polling interval 1 second or less does not matter much when looking at these temperature rise times 

After that in more then an hour it slowly creeps up to 85. I believe the design is so that the SOC, under normal circumstances, can run at 1.35 GHz without throttling frequency, without heatsink. It just needs a safeguard for different circumstances.

Most of these SOCs can also run in industrial grade circumstances, which means up to 85 degrees ambient temperature already . If not industrial then this would be 60 degrees ambient already 

But only someone at Mediatek can confirm this 

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On Jun 24, 2021, 12:21 PM, at 12:21 PM, Daniel Lezcano [off-list ref] wrote:
On 24/06/2021 11:59, Eric Woudstra wrote:
quoted
For Marvell:

https://www.google.com/url?sa=t&source=web&rct=j&url=https://wiki.kobol.io/helios4/files/som/brochure_a38x_microsom_2017-09-05.pdf
quoted
Armada38x maximum die temperature 115 degrees Celcius. They really
get hotter then 100.
quoted
But for mt7622 I cannot find this value
Found that:

https://download.kamami.pl/p579344-MT7622A_Datasheet_for_BananaPi_Only%281%29.pdf

Chapter 3.3 - Thermal Characteristics

Given the values I suggest:

- Passive - 80°C

- Hot - 90°C

- Critical - 100°C

And passive polling set to 250ms.

It sounds like the sensor is not supporting the interrupt mode yet, so
a
big gap is needed with the Tj IMO to give the time to detect the trip
point crossing with the polling.
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On Jun 23, 2021, 10:08 PM, at 10:08 PM, Daniel Lezcano
[off-list ref] wrote:
quoted
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On 23/06/2021 20:43, Eric Woudstra wrote:
quoted
I choose "hot" before, because 87 degrees seems ok to start
frequency
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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
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to use 87 degrees But maybe someone at Mediatek can give some more
details about operating temperatures.
Sometimes, the SoC vendor puts a high temperature in the DT just to
export the thermal zone and deal with it from userspace. So putting
the
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high temp allow the userspace (usually a thermal engine - Android
stuff)
to deal with the mitigation without a kernel interaction.

Having more than 100°C could be this kind of setup. Only the
operating
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temperature from the hardware documentation will tell the safe
temperature for the silicon.

IMO, 77°C is a good compromise until getting the documented temp.
87°C
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sounds to me a bit too hot.
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It may be possible to leave the active map in the device tree as
some
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users of the bananapi might choose to install a fan as it is one of
the options.
The active trip only makes sense if the cooling device is a fan (or
any
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active device), so the mapping points to a fan node, like:

https://git.kernel.org/pub/scm/linux/kernel/git/thermal/linux.git/tree/arch/arm64/boot/dts/rockchip/rk3399-khadas-edge.dtsi#n192
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If there is no such [pwm] fan output on the board, no active trip
point
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should be added.
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On Jun 23, 2021, 5:58 PM, at 5:58 PM, Daniel Lezcano
[off-list ref] wrote:
quoted
On 23/06/2021 17:35, Eric Woudstra wrote:
quoted
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.
quoted
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@43000000 {

thermal-zones { cpu_thermal: cpu-thermal { -
polling-delay-passive = <1000>; +			polling-delay-passive = <250>;
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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>; }; -
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-				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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SoCs
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Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

-- 
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

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