linux-kernel - Re: [PATCH RFC 0/8] Introduce warming in thermal framework

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Date:   Mon, 19 Oct 2020 21:22:59 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Thara Gopinath <thara.gopinath@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Linux PM list <linux-pm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        lukasz.luba@....com, amitk@...nel.org
Subject: Re: [PATCH RFC 0/8] Introduce warming in thermal framework

On 19/10/2020 20:42, Thara Gopinath wrote:
> On Wed, 16 Sep 2020 at 23:22, Thara Gopinath <thara.gopinath@...aro.org> wrote:
>>
>> Thermal framework today supports monitoring for rising temperatures and
>> subsequently initiating cooling action in case of a thermal trip point
>> being crossed. There are scenarios where a SoC need warming mitigating
>> action to be activated if the temperature falls below a cetain permissible
>> limit.  Since warming action can be considered mirror opposite of cooling
>> action, most of the thermal framework can be re-used to achieve this. The
>> key assumption in this patch series is that a device can act either as a
>> warming device or a cooling device and not as both.
>>
>> In order to support warming three extensions are needed in the thermal
>> framework.
>>
>> 1. Indication that a trip point is being monitored for falling temperature
>> and not rising temperature. We discussed two different ways to achieve this
>> during LPC. First option is to introduce a new trip type to indicate that a
>> trip is a cold trip(THERMAL_TRIP_COLD). The second option is to introduce a
>> new property for trip point that will indicate whether a trip point is
>> being monitored for rising temperature or falling temperature. The patch
>> series(patches 1-4) chooses the second approach since it allows trip points
>> of any type to be monitored for rising or falling temperature.Also this was
>> the preferred approach when discussed during LPC. The approach that
>> introduces a new cold trip type was posted on the list earlier as a RFC and
>> can be found at [1].
>>
>> 2. Extend the exisitng governors to handle monitoring of falling
>> temperature. The patch series(patches 5 & 6) extends the step wise governor
>> to monitor the falling temperature.Other governors return doing nothing if
>> the trip point they are being called for is being monitored for falling
>> temperature. The governors' mitigate function is called "throttle" in the
>> thermal framework and with this patch series it is a misnomer as the
>> function is called for both throttling and warming up. Ideally
>> "throttle" should be renamed to "mitigate" to improve readability of code.
>> The renaming is not part of this series.
>>
>> 3. Finally, the cooling device framework itself can be reused for a warming
>> device. As stated before a device can act either as a warming device or a
>> cooling device and not as both.  With this the cooling state in the
>> framework can be considered as mitigating state with 0 as the state with no
>> thermal mitigation and higher the number higher the thermal mitigation.
>> Again what affects the code readability and comprehension is the term
>> "cooling" which is a misnomer here. Ideally the term "cooling" should be
>> renamed to "mitigating" and hence thermal_cooling_device will become
>> thermal_mitgating_device. The renaming is not part of the patch series as
>> even though the renaming is a simple search-replace, it will change a lot
>> of files.  The patch series(patches 7 & 8) instead introduces a minimal set
>> of _warming_device_ apis to register and unregister warming devices which
>> internally is identical to the _cooling_device_ counterpart.
> 
> Gentle ping for review..

Pong, review before the end of this week.



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