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Subject: Re: [PATCH v2 47/48] ARM: tegra: ventana: Support CPU voltage scaling
 and thermal throttling
To:     Dmitry Osipenko <digetx@gmail.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Mark Brown <broonie@kernel.org>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Peter Geis <pgwipeout@gmail.com>,
        Nicolas Chauvet <kwizart@gmail.com>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Kevin Hilman <khilman@kernel.org>,
        Peter De Schrijver <pdeschrijver@nvidia.com>,
        Viresh Kumar <vireshk@kernel.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>
Cc:     devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-media@vger.kernel.org, linux-tegra@vger.kernel.org,
        linux-clk@vger.kernel.org
References: <20201217180638.22748-1-digetx@gmail.com>
 <20201217180638.22748-48-digetx@gmail.com>
 <91139f8b-0b83-dd8a-ba53-8e7a499e6344@linaro.org>
 <b39ebfc1-42b3-1fa7-efe4-6ecbc8cfcb50@gmail.com>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
Message-ID: <776e0e84-e395-2bfb-f1ee-c34864b1cf16@linaro.org>
Date:   Thu, 17 Dec 2020 20:36:12 +0100
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On 17/12/2020 20:01, Dmitry Osipenko wrote:
> 17.12.2020 21:28, Daniel Lezcano пишет:
>> On 17/12/2020 19:06, Dmitry Osipenko wrote:
>>> Enable CPU voltage scaling and thermal throttling on Tegra20 Ventana board.
>>>
>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>>> ---
>>>  arch/arm/boot/dts/tegra20-ventana.dts | 40 ++++++++++++++++++++++++++-
>>>  1 file changed, 39 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm/boot/dts/tegra20-ventana.dts b/arch/arm/boot/dts/tegra20-ventana.dts
>>> index 14ace2ef749c..c2d9f38960bc 100644
>>> --- a/arch/arm/boot/dts/tegra20-ventana.dts
>>> +++ b/arch/arm/boot/dts/tegra20-ventana.dts
>>> @@ -2,8 +2,10 @@
>>>  /dts-v1/;
>>>  
>>>  #include <dt-bindings/input/input.h>
>>> +#include <dt-bindings/thermal/thermal.h>
>>>  #include "tegra20.dtsi"
>>>  #include "tegra20-cpu-opp.dtsi"
>>> +#include "tegra20-cpu-opp-microvolt.dtsi"
>>>  
>>>  / {
>>>  	model = "NVIDIA Tegra20 Ventana evaluation board";
>>> @@ -527,9 +529,10 @@ ldo_rtc {
>>>  			};
>>>  		};
>>>  
>>> -		temperature-sensor@4c {
>>> +		nct1008: temperature-sensor@4c {
>>>  			compatible = "onnn,nct1008";
>>>  			reg = <0x4c>;
>>> +			#thermal-sensor-cells = <1>;
>>>  		};
>>>  	};
>>>  
>>> @@ -615,10 +618,13 @@ clk32k_in: clock@0 {
>>>  
>>>  	cpus {
>>>  		cpu0: cpu@0 {
>>> +			cpu-supply = <&vdd_cpu>;
>>>  			operating-points-v2 = <&cpu0_opp_table>;
>>> +			#cooling-cells = <2>;
>>>  		};
>>>  
>>>  		cpu@1 {
>>> +			cpu-supply = <&vdd_cpu>;
>>>  			operating-points-v2 = <&cpu0_opp_table>;
>>>  		};
>>>  	};
>>> @@ -717,4 +723,36 @@ sound {
>>>  			 <&tegra_car TEGRA20_CLK_CDEV1>;
>>>  		clock-names = "pll_a", "pll_a_out0", "mclk";
>>>  	};
>>> +
>>> +	thermal-zones {
>>> +		cpu-thermal {
>>> +			polling-delay-passive = <1000>; /* milliseconds */
>>> +			polling-delay = <5000>; /* milliseconds */
>>> +
>>> +			thermal-sensors = <&nct1008 1>;
>>> +
>>> +			trips {
>>> +				trip0: cpu-alert0 {
>>> +					/* start throttling at 50C */
>>> +					temperature = <50000>;
>>> +					hysteresis = <200>;
>>
>> Did you mean <2000> ?
> 
> The <200> is correct.
> 
> Please see this commit for example:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2b22393b27670b45a2c870bce3df6579efd9a86a

Ok, thanks for the pointer.

>>> +					type = "passive";
>>> +				};
>>> +
>>> +				trip1: cpu-crit {
>>> +					/* shut down at 60C */
>>> +					temperature = <60000>;
>>> +					hysteresis = <2000>;
>>
>> I think you can drop the hysteresis here, when the critical temperature
>> is reached, there is an emergency shutdown.
> 
> Yes, perhaps you're right. Hysteresis doesn't make sense for a critical
> trip. I'll improve it in the next revision, thanks.
> 
>> 50°C and 60°C sound very low values, no ?
> 
> Tegra20 CPU is very cold in comparison to later generations, it should
> stay under 50°C even at a full load.

Interesting, thanks.

>>> +					type = "critical";
>>> +				};
>>> +			};
>>> +
>>> +			cooling-maps {
>>> +				map0 {
>>> +					trip = <&trip0>;
>>> +					cooling-device = <&cpu0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
>>
>> You should add all CPUs here.
> 
> 
> All CPU cores are coupled on Tegra in regards to CPUFreq, hence I think
> it won't make any difference if secondary CPU cores will be added here,
> isn't it?

The explanation is in the description of commit ef4734500407ce4d


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