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Subject: Re: [Patch v5 2/6] thermal: qcom: Add support for LMh driver
To:     Daniel Lezcano <daniel.lezcano@linaro.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>
Cc:     agross@kernel.org, rui.zhang@intel.com, viresh.kumar@linaro.org,
        rjw@rjwysocki.net, robh+dt@kernel.org, steev@kali.org,
        tdas@codeaurora.org, mka@chromium.org,
        linux-arm-msm@vger.kernel.org, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
References: <20210809191605.3742979-1-thara.gopinath@linaro.org>
 <20210809191605.3742979-3-thara.gopinath@linaro.org>
 <fcbb6d64-7e39-7f03-e76c-512946124777@linaro.org> <YSO5Njg3DXo64InF@ripper>
 <a216c89d-6cd5-326d-f203-f48caaf2a096@linaro.org>
From:   Thara Gopinath <thara.gopinath@linaro.org>
Message-ID: <299e2a59-ae4e-278d-200d-630f055c1411@linaro.org>
Date:   Tue, 31 Aug 2021 10:52:27 -0400
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On 8/23/21 11:57 AM, Daniel Lezcano wrote:
> 
> Hi Bjorn,
> 
> On 23/08/2021 17:05, Bjorn Andersson wrote:
>> On Sat 21 Aug 02:41 PDT 2021, Daniel Lezcano wrote:
>>
>>>
>>> Hi Thara,
>>>
>>> On 09/08/2021 21:16, Thara Gopinath wrote:
>>>> Driver enabling various pieces of Limits Management Hardware(LMh) for cpu
>>>> cluster0 and cpu cluster1 namely kick starting monitoring of temperature,
>>>> current, battery current violations, enabling reliability algorithm and
>>>> setting up various temperature limits.
>>>>
>>>> The following has been explained in the cover letter. I am including this
>>>> here so that this remains in the commit message as well.
>>>>
>>>> LMh is a hardware infrastructure on some Qualcomm SoCs that can enforce
>>>> temperature and current limits as programmed by software for certain IPs
>>>> like CPU. On many newer LMh is configured by firmware/TZ and no programming
>>>> is needed from the kernel side. But on certain SoCs like sdm845 the
>>>> firmware does not do a complete programming of the h/w. On such soc's
>>>> kernel software has to explicitly set up the temperature limits and turn on
>>>> various monitoring and enforcing algorithms on the hardware.
>>>>
>>>> Tested-by: Steev Klimaszewski <steev@kali.org> # Lenovo Yoga C630
>>>> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
>>>
>>> Is it possible to have an option to disable/enable the LMh driver at
>>> runtime, for instance with a module parameter ?
>>>
>>
>> Are you referring to being able to disable the hardware throttling, or
>> the driver's changes to thermal pressure?
> 
> The former.

Hi Daniel,

It is not recommended to turn off LMh once enabled. From h/w point of 
view, it can be done for debug purposes but it is not to be implemented 
as a feature.


> 
>> I'm not aware of any way to disable the hardware. I do remember that
>> there was some experiments done (with a hacked up boot chain) early on
>> and iirc it was concluded that it's not a good idea.
> 
> My objective was to test the board with the thermal framework handling
> the mitigation instead of the hardware.
> 
> I guess I can set the hardware temperature higher than the thermal zone
> temperature.

Right. Also remember that  patch 5 in this series removes the cooling 
devices for the cpu thermal zones. So if you are testing this you will 
have to add them back.

> 
> On which sensor the lmh does refer to ? The cluster one ?
> 
> (by the way the thermal zone temperatures per core are lower by 5°C than
> the hardware mitigation ? is it done on purpose ?)


So IIUC, it refers to tsens for individual cpus and collates the input. 
But the documentation is not clear on this one. I took the mitigation 
temperature from downstream code. Yes I did realize that the thermal 
zone trip1 temp is 90 degree where as the LMh mitigation point is 95 
degree. My thinking is this is because the h/w mitigation can happen 
faster than s/w and hence the 5 degree bump up in temperature.

> 
>> Either way, if there is a way and there is a use for it, we can always
>> add such parameter incrementally. So I suggest that we merge this as is.
> 
> Yes, that was for my information. It is already merged.

Thank you very much

> 
> Thanks
> 
>    -- Daniel
> 

-- 
Warm Regards
Thara (She/Her/Hers)