linux-kernel - Re: [PATCH V15 RESEND 5/5] arm64: dts: imx: add i.MX8QXP thermal support

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Message-ID: <59784965-dba6-5878-68fa-5657f3e5f02e@linaro.org>
Date:   Sat, 22 Feb 2020 08:51:57 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Anson Huang <anson.huang@....com>
Cc:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
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        "kernel@...gutronix.de" <kernel@...gutronix.de>,
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        Leonard Crestez <leonard.crestez@....com>,
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Subject: Re: [PATCH V15 RESEND 5/5] arm64: dts: imx: add i.MX8QXP thermal
 support

On 22/02/2020 00:53, Anson Huang wrote:
> Hi, Daniel
> 

[ ... ]

>>> +
>>> +	thermal_zones: thermal-zones {
>>> +		cpu-thermal0 {
>>> +			polling-delay-passive = <250>;
>>> +			polling-delay = <2000>;
>>> +			thermal-sensors = <&tsens IMX_SC_R_SYSTEM>;
>>> +			trips {
>>> +				cpu_alert0: trip0 {
>>> +					temperature = <107000>;
>>> +					hysteresis = <2000>;
>>> +					type = "passive";
>>> +				};
>>
>> May be you can add a 'hot' trip point before 'critical' for future use before
>> reaching the emergency shutdown.
> 
> The 'passive' trip is actually the 'hot' trip point you mentioned, and I have combined it to
> below cooling map which will throttle cpu-freq when passive (hot) point is reached.
> We all use 'passive' as 'hot' alarm and trigger cpu-freq throttle on i.MX platforms. 

Sorry, I'm not sure to get the point. A 'hot' trip point is not a
'passive' trip point. The 'hot' trip point is a critical temperature and
a notification is raised [1][2].

It is the last chance for the system to do something before the next
trip point 'critical' is reached and where an emergency shutdown is done.

The 'passive' trip point is the target temperature for mitigation in a
normal situation when the system is loaded.

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/thermal/thermal_core.c#n288
[2]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/thermal/thermal_core.c#n420




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