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: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220213025739.2561834-8-liambeguin@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 46947c6..e31a934 100644 (file)
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -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);