linux-kernel - Re: [RFC] ARM: dts: omap36xx: Enable thermal throttling

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Date:   Fri, 13 Sep 2019 00:33:40 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Adam Ford <aford173@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Linux-OMAP <linux-omap@...r.kernel.org>,
        "H. Nikolaus Schaller" <hns@...delico.com>,
        Tony Lindgren <tony@...mide.com>,
        André Roth <neolynx@...il.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andreas Kemnade <andreas@...nade.info>,
        Nishanth Menon <nm@...com>, Adam Ford <adam.ford@...icpd.com>
Subject: Re: [RFC] ARM: dts: omap36xx: Enable thermal throttling


Hi Adam,

On 12/09/2019 23:19, Adam Ford wrote:
> On Thu, Sep 12, 2019 at 4:12 PM Daniel Lezcano
> <daniel.lezcano@...aro.org> wrote:
>>
>> On 12/09/2019 20:30, Adam Ford wrote:
>>> The thermal sensor in the omap3 family isn't accurate, but it's
>>> better than nothing.  The various OPP's enabled for the omap3630
>>> support up to OPP1G, however the datasheet for the DM3730 states
>>> that OPP130 and OPP1G are not available above TJ of 90C.
>>>
>>> This patch configures the thermal throttling to limit the
>>> operating points of the omap3630 to Only OPP50 and OPP100 if
>>> the thermal sensor reads a value above 90C.

Oh, that's a very interesting use case.

AFAICT the thermal framework is not designed to deal with this
situation. I agree this setup may work (even if I'm not convinced about
the stability of the whole).

May be Viresh can help for the cpufreq side?

>> Out of curiosity, what are the OPP50 and OPP100 mentioned above? and
>> what does mean "OPP130 and OPP1G are not available above TJ of 90C"?
>>
> OPP130 is the 800 MHz and OPP1G is 1GHz operating point.
> The 90C is the max junction temperature.  When the temperature exceeds
> 90C, the processor is not designed to operate at 800+ MHz.  The
> statement itself is a direct quote from the public datasheet for the
> dm3730, Table 4-19.

> The datasheet is: http://www.ti.com/lit/ds/symlink/dm3730.pdf

It is ambiguous how it is stated:

"OPP130 and OPP1G are not available above TJ of 90C"

that can be interpreted the OPP is disabled by the hardware, no?

> The operating points were updated in [1], but they haven't yet been
> fully applied yet, but during the discussion, the question came about
> regarding how to limit the speed at high temp, so that's why this
> patch was done.
> 
> [1] - https://patchwork.kernel.org/patch/11141643/

I see, you switched to opp-v2.

Thanks for the detailed answer.



>> I don't see the connection between these OPP names and the definition in
>> the DT.
>>
>>> Signed-off-by: Adam Ford <aford173@...il.com>
>>>
>>> diff --git a/arch/arm/boot/dts/omap36xx.dtsi b/arch/arm/boot/dts/omap36xx.dtsi
>>> index 4bb4f534afe2..58b9d347019f 100644
>>> --- a/arch/arm/boot/dts/omap36xx.dtsi
>>> +++ b/arch/arm/boot/dts/omap36xx.dtsi
>>> @@ -25,6 +25,7 @@
>>>
>>>                       vbb-supply = <&abb_mpu_iva>;
>>>                       clock-latency = <300000>; /* From omap-cpufreq driver */
>>> +                     #cooling-cells = <2>;
>>>               };
>>>       };
>>>
>>> @@ -195,6 +196,31 @@
>>>       };
>>>  };
>>>
>>> +&cpu_thermal {
>>> +     cpu_trips: trips {
>>> +             /* OPP130 and OPP1G are not available above TJ of 90C. */
>>> +             cpu_alert0: cpu_alert {
>>> +                     temperature = <90000>; /* millicelsius */
>>> +                     hysteresis = <2000>; /* millicelsius */
>>> +                     type = "passive";
>>> +             };
>>> +
>>> +             cpu_crit: cpu_crit {
>>> +                     temperature = <125000>; /* millicelsius */
>>> +                     hysteresis = <2000>; /* millicelsius */
>>> +                     type = "critical";
>>> +             };
>>> +     };
>>> +
>>> +     cpu_cooling_maps: cooling-maps {
>>> +             map0 {
>>> +                     trip = <&cpu_alert0>;
>>> +                     /* Only allow OPP50 and OPP100 */
>>> +                     cooling-device = <&cpu 0 1>;
>>> +             };
>>> +     };
>>> +};
>>> +
>>>  /* OMAP3630 needs dss_96m_fck for VENC */
>>>  &venc {
>>>       clocks = <&dss_tv_fck>, <&dss_96m_fck>;
>>>
>>
>>
>> --
>>  <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
>>
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