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. The ADC interface is provided
through the IIO framework.
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: Laxman Dewangan <ldewangan@xxxxxxxxxx>
---
.../bindings/thermal/thermal-generic-adc.txt | 86 ++++++++++++++++++++++
1 file changed, 86 insertions(+)
create mode 100644 Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt
diff --git a/Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt b/Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt
new file mode 100644
index 0000000..6b3e715
--- /dev/null
+++ b/Documentation/devicetree/bindings/thermal/thermal-generic-adc.txt
@@ -0,0 +1,86 @@
+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. The voltage read across the sensor is mapped to temperature using
+voltage-temperature lookup table.
+
+This driver provides the interface to sensor-ADC interconnection and
+the relation ship between ADC read value and temperature.
+
+Required properties:
+===================
+- compatible: Must be "generic-adc-thermal".
+- lower-temperature: Lower temperature for the lookup table
+ in millicelsius.
+- upper-temperature: Upper temperature for the lookup table
+ in millicelsius.
+- step-temperature: The temperature steps for the reading ADC
+ value in millicelsius.
+- temperature-lookup-table: The ADC reading value on each step of the
+ temperature starting from lower temperature
+ to upper temperature.
+ When ADC is read, the value is looked up on the
+ table to get the equivalent temperature.
+- #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>;
+ };
+};
+
+thermal-sensor@1 {
+ compatible = "generic-adc-thermal";
+ #thermal-sensor-cells = <0>;
+ io-channels = <&ads1015 1>;
+ io-channel-names = "sensor-channel";
+ lower-temperature = <(-40000)>;
+ upper-temperature = <125000>;
+ step-temperature = <1000>;
+ temperature-lookup-table = <2578 2577 2576 2575 2574
+ 2573 2572 2571 2569 2568
+ 2567 2565 2563 2561 2559
+ ::::::::::
+ 254 247 240 233 226 220
+ 214 208>;
+};
+
+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>;
+ writable;
+ };
+ };
+
+ cooling-maps {
+ map0 {
+ trip = <&therm_est_trip>;
+ cooling-device = <&dummy_cool_dev THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
+ contribution = <100>;
+ cdev-type = "therm_est_activ";
+ };
+ };
+
+ };
+};
--
2.1.4
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