linux-kernel - Re: [RFC 1/2] dt-bindings: thermal: sprd: Add virtual thermal documentation

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Message-ID: <fc2e095f-d417-1547-4075-9ece1aeaaf4d@arm.com>
Date:   Fri, 27 Nov 2020 13:58:46 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>, gao.yunxiao6@...il.com,
        rui.zhang@...el.com, amitk@...nel.org, robh+dt@...nel.org,
        javi.merino@...nel.org
Cc:     linux-pm@...r.kernel.org, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        orsonzhai@...il.com, zhang.lyra@...il.com,
        "jeson.gao" <jeson.gao@...soc.com>
Subject: Re: [RFC 1/2] dt-bindings: thermal: sprd: Add virtual thermal
 documentation



On 11/27/20 1:26 PM, Daniel Lezcano wrote:
> 
> Hi Lukasz,
> 
> On 27/11/2020 10:27, Lukasz Luba wrote:
>>
>>
>> On 11/27/20 8:35 AM, gao.yunxiao6@...il.com wrote:
>>> From: "jeson.gao" <jeson.gao@...soc.com>
>>>
>>> virtual thermal node definition description in dts file
>>>
>>> Signed-off-by: jeson.gao <jeson.gao@...soc.com>
>>> ---
> 
> [ ... ]
> 
>> It's coming back. There were attempts to solve this problem.
>> Javi tried to solved this using hierarchical thermal zones [1].
>> It was even agreed (IIRC during LPC) but couldn't continue. Then Eduardo
>> was going to continue this (last message at [3]). Unfortunately,
>> development stopped.
>>
>> I also have out-of-tree similar implementation for my Odroid-xu4,
>> which does no have an 'SoC' sensor, but have CPU sensors and needs
>> some aggregation function to get temperature.
>>
>> I can pick up Javi's patches and continue 'hierarchical thermal zones'
>> approach.
>>
>> Javi, Daniel, Rui what do you think?
> 
> I already worked on the hierarchical thermal zones and my opinion is
> that fits not really well.
> 
> We want to define a new feature because the thermal framework is built
> on the 1:1 relationship between a governor and a thermal zone.
> 
> Practically speaking, we want to mitigate two thermal zones from one
> governor, especially here the IPA governor.
> 
> The DTPM framework is being implemented to solve that by providing an
> automatic power rebalancing between the power manageable capable devices.
> 
> In our case, the IPA would stick on the 'sustainable-power' resulting on
> the aggregation of the two performance domains and set the power limit
> on the parent node. The automatic power rebalancing will ensure maximum
> throughput between the two performance domains instead of capping the whole.
> 
> 

Make sense. Thank you for sharing valuable opinion.

Regards,
Lukasz