Commit bd56c1e9 authored by Linus Walleij's avatar Linus Walleij Committed by Guenter Roeck
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hwmon: (ntc_thermistor) Use library interpolation 



The kernel has a helper function for linear interpolation so
use it. It incidentally makes the code easier to read as well.

Tested on the ST-Ericsson HREFv60plus hardware reference design
with two thermistors forming a thermal zone.

Cc: Peter Rosin <peda@axentia.se>
Cc: Chris Lesiak <chris.lesiak@licor.com>
Cc: linux-iio@vger.kernel.org
Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20210704222014.12058-1-linus.walleij@linaro.org


Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
parent 02c9dce4

drivers/hwmon/ntc_thermistor.c

+11 −9
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ 
#include <linux/err.h>

#include <linux/of.h>

#include <linux/of_device.h>

#include <linux/fixp-arith.h>



#include <linux/platform_data/ntc_thermistor.h>
@@ -549,15 +550,16 @@ static int get_temp_mc(struct ntc_data *data, unsigned int ohm) 
	int temp;



	lookup_comp(data, ohm, &low, &high);

	if (low == high) {

		/* Unable to use linear approximation */

		temp = data->comp[low].temp_c * 1000;

	} else {

		temp = data->comp[low].temp_c * 1000 +

			((data->comp[high].temp_c - data->comp[low].temp_c) *

			 1000 * ((int)ohm - (int)data->comp[low].ohm)) /

			((int)data->comp[high].ohm - (int)data->comp[low].ohm);

	}

	/*

	 * First multiplying the table temperatures with 1000 to get to

	 * millicentigrades (which is what we want) and then interpolating

	 * will give the best precision.

	 */

	temp = fixp_linear_interpolate(data->comp[low].ohm,

				       data->comp[low].temp_c * 1000,

				       data->comp[high].ohm,

				       data->comp[high].temp_c * 1000,

				       ohm);

	return temp;

}