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

   1 General Purpose Analog To Digital Converter (ADC) based thermal sensor.
   2
   3 On some of platforms, thermal sensor like thermistors are connected to
   4 one of ADC channel and sensor resistance is read via voltage across the
   5 sensor resistor. The voltage read across the sensor is mapped to
   6 temperature using voltage-temperature lookup table.
   7
   8 Required properties:
   9 ===================
  10 - compatible:                Must be "generic-adc-thermal".
  11 - #thermal-sensor-cells:     Should be 1. See ./thermal.txt for a description
  12                              of this property.
  13 Optional properties:
  14 ===================
  15 - temperature-lookup-table:  Two dimensional array of Integer; lookup table
  16                              to map the relation between ADC value and
  17                              temperature. When ADC is read, the value is
  18                              looked up on the table to get the equivalent
  19                              temperature.
  20
  21                              The first value of the each row of array is the
  22                              temperature in milliCelsius and second value of
  23                              the each row of array is the ADC read value.
  24
  25                              If not specified, driver assumes the ADC channel
  26                              gives milliCelsius directly.
  27
  28 Example :
  29 #include <dt-bindings/thermal/thermal.h>
  30
  31 i2c@7000c400 {
  32         ads1015: ads1015@4a {
  33                 reg = <0x4a>;
  34                 compatible = "ads1015";
  35                 sampling-frequency = <3300>;
  36                 #io-channel-cells = <1>;
  37         };
  38 };
  39
  40 tboard_thermistor: thermal-sensor {
  41         compatible = "generic-adc-thermal";
  42         #thermal-sensor-cells = <0>;
  43         io-channels = <&ads1015 1>;
  44         io-channel-names = "sensor-channel";
  45         temperature-lookup-table = <    (-40000) 2578
  46                                         (-39000) 2577
  47                                         (-38000) 2576
  48                                         (-37000) 2575
  49                                         (-36000) 2574
  50                                         (-35000) 2573
  51                                         (-34000) 2572
  52                                         (-33000) 2571
  53                                         (-32000) 2569
  54                                         (-31000) 2568
  55                                         (-30000) 2567
  56                                         ::::::::::
  57                                         118000 254
  58                                         119000 247
  59                                         120000 240
  60                                         121000 233
  61                                         122000 226
  62                                         123000 220
  63                                         124000 214
  64                                         125000 208>;
  65 };
  66
  67 dummy_cool_dev: dummy-cool-dev {
  68         compatible = "dummy-cooling-dev";
  69         #cooling-cells = <2>; /* min followed by max */
  70 };
  71
  72 thermal-zones {
  73         Tboard {
  74                 polling-delay = <15000>; /* milliseconds */
  75                 polling-delay-passive = <0>; /* milliseconds */
  76                 thermal-sensors = <&tboard_thermistor>;
  77
  78                 trips {
  79                         therm_est_trip: therm_est_trip {
  80                                 temperature = <40000>;
  81                                 type = "active";
  82                                 hysteresis = <1000>;
  83                         };
  84                 };
  85
  86                 cooling-maps {
  87                         map0 {
  88                                 trip = <&therm_est_trip>;
  89                                 cooling-device = <&dummy_cool_dev THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
  90                                 contribution = <100>;
  91                         };
  92
  93                 };
  94         };
  95 };