Commit 278fe1d2 authored by Liam Beguin's avatar Liam Beguin Committed by Jonathan Cameron
Browse files

iio: afe: rescale: add RTD temperature sensor support 



An RTD (Resistance Temperature Detector) is a kind of temperature
sensor used to get a linear voltage to temperature reading within a
give range (usually 0 to 100 degrees Celsius). Common types of RTDs
include PT100, PT500, and PT1000.

Signed-off-by: default avatarLiam Beguin <liambeguin@gmail.com>
Reviewed-by: default avatarPeter Rosin <peda@axentia.se>
Reviewed-by: default avatarAndy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220213025739.2561834-8-liambeguin@gmail.com


Signed-off-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
parent 8e74a48d

drivers/iio/afe/iio-rescale.c

+48 −0
Original line number Diff line number Diff line
@@ -394,10 +394,52 @@ static int rescale_voltage_divider_props(struct device *dev, 
	return 0;

}



static int rescale_temp_sense_rtd_props(struct device *dev,

					struct rescale *rescale)

{

	u32 factor;

	u32 alpha;

	u32 iexc;

	u32 tmp;

	int ret;

	u32 r0;



	ret = device_property_read_u32(dev, "excitation-current-microamp",

				       &iexc);

	if (ret) {

		dev_err(dev, "failed to read excitation-current-microamp: %d\n",

			ret);

		return ret;

	}



	ret = device_property_read_u32(dev, "alpha-ppm-per-celsius", &alpha);

	if (ret) {

		dev_err(dev, "failed to read alpha-ppm-per-celsius: %d\n",

			ret);

		return ret;

	}



	ret = device_property_read_u32(dev, "r-naught-ohms", &r0);

	if (ret) {

		dev_err(dev, "failed to read r-naught-ohms: %d\n", ret);

		return ret;

	}



	tmp = r0 * iexc * alpha / 1000000;

	factor = gcd(tmp, 1000000);

	rescale->numerator = 1000000 / factor;

	rescale->denominator = tmp / factor;



	rescale->offset = -1 * ((r0 * iexc) / 1000);



	return 0;

}



enum rescale_variant {

	CURRENT_SENSE_AMPLIFIER,

	CURRENT_SENSE_SHUNT,

	VOLTAGE_DIVIDER,

	TEMP_SENSE_RTD,

};



static const struct rescale_cfg rescale_cfg[] = {
@@ -413,6 +455,10 @@ static const struct rescale_cfg rescale_cfg[] = { 
		.type = IIO_VOLTAGE,

		.props = rescale_voltage_divider_props,

	},

	[TEMP_SENSE_RTD] = {

		.type = IIO_TEMP,

		.props = rescale_temp_sense_rtd_props,

	},

};



static const struct of_device_id rescale_match[] = {
@@ -422,6 +468,8 @@ static const struct of_device_id rescale_match[] = { 
	  .data = &rescale_cfg[CURRENT_SENSE_SHUNT], },

	{ .compatible = "voltage-divider",

	  .data = &rescale_cfg[VOLTAGE_DIVIDER], },

	{ .compatible = "temperature-sense-rtd",

	  .data = &rescale_cfg[TEMP_SENSE_RTD], },

	{ /* sentinel */ }

};

MODULE_DEVICE_TABLE(of, rescale_match);