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Commit 9e389e38 authored by Laxman Dewangan's avatar Laxman Dewangan Committed by Eduardo Valentin
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thermal: generic-adc: Add DT binding for ADC based thermal sensor 



Sometimes, thermal sensors like NCT thermistors are connected to
the ADC channel. The temperature is read by reading the voltage
across the sensor resistance via ADC and referring the lookup
table for ADC value to temperature.

Add DT binding doc for the ADC based thermal sensor driver to
detail the DT property and provide the example for how to use it.

Signed-off-by: default avatarLaxman Dewangan <ldewangan@nvidia.com>
Acked-by: default avatarRob Herring <rob@kernel.org>
Signed-off-by: default avatarEduardo Valentin <edubezval@gmail.com>
parent f3500980

Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt

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General Purpose Analog To Digital Converter (ADC) based thermal sensor.



On some of platforms, thermal sensor like thermistors are connected to

one of ADC channel and sensor resistance is read via voltage across the

sensor resistor. The voltage read across the sensor is mapped to

temperature using voltage-temperature lookup table.



Required properties:

===================

- compatible:		     Must be "generic-adc-thermal".

- temperature-lookup-table:  Two dimensional array of Integer; lookup table

			     to map the relation between ADC value and

			     temperature. When ADC is read, the value is

			     looked up on the table to get the equivalent

			     temperature.

			     The first value of the each row of array is the

			     temperature in milliCelsius and second value of

			     the each row of array is the ADC read value.

- #thermal-sensor-cells:     Should be 1. See ./thermal.txt for a description

			     of this property.



Example :

#include <dt-bindings/thermal/thermal.h>



i2c@7000c400 {

	ads1015: ads1015@4a {

		reg = <0x4a>;

		compatible = "ads1015";

		sampling-frequency = <3300>;

		#io-channel-cells = <1>;

	};

};



tboard_thermistor: thermal-sensor {

	compatible = "generic-adc-thermal";

	#thermal-sensor-cells = <0>;

	io-channels = <&ads1015 1>;

	io-channel-names = "sensor-channel";

	temperature-lookup-table = <    (-40000) 2578

					(-39000) 2577

					(-38000) 2576

					(-37000) 2575

					(-36000) 2574

					(-35000) 2573

					(-34000) 2572

					(-33000) 2571

					(-32000) 2569

					(-31000) 2568

					(-30000) 2567

					::::::::::

					118000 254

					119000 247

					120000 240

					121000 233

					122000 226

					123000 220

					124000 214

					125000 208>;

};



dummy_cool_dev: dummy-cool-dev {

	compatible = "dummy-cooling-dev";

	#cooling-cells = <2>; /* min followed by max */

};



thermal-zones {

	Tboard {

		polling-delay = <15000>; /* milliseconds */

		polling-delay-passive = <0>; /* milliseconds */

		thermal-sensors = <&tboard_thermistor>;



		trips {

			therm_est_trip: therm_est_trip {

				temperature = <40000>;

				type = "active";

				hysteresis = <1000>;

			};

		};



		cooling-maps {

			map0 {

				trip = <&therm_est_trip>;

				cooling-device = <&dummy_cool_dev THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;

				contribution = <100>;

			};



		};

	};

};