On Wed, Apr 06, 2016 at 03:33:05PM +0530, Laxman Dewangan wrote:
> 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.
How about when you have a sensor that does not have a nice linear
stepping correlation ?
> +- 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.
I would say, we would need to support a two dimensional table here..
> +- #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;
Not sure about writable property, where is it described?
> + };
> + };
> +
> + 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";
Not sure about cdev-type property, where is it described?
> + };
> + };
> +
> + };
> +};
> --
> 2.1.4
>
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