linux-kernel - Re: [Patch v5 2/6] thermal: qcom: Add support for LMh driver

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Date:   Mon, 23 Aug 2021 17:57:02 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Thara Gopinath <thara.gopinath@...aro.org>, agross@...nel.org,
        rui.zhang@...el.com, viresh.kumar@...aro.org, rjw@...ysocki.net,
        robh+dt@...nel.org, steev@...i.org, tdas@...eaurora.org,
        mka@...omium.org, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [Patch v5 2/6] thermal: qcom: Add support for LMh driver


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@...i.org> # Lenovo Yoga C630
>>> Signed-off-by: Thara Gopinath <thara.gopinath@...aro.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.

> 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.

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 ?)

> 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.

Thanks

  -- Daniel

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