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authorLinus Walleij <linus.walleij@linaro.org>2021-07-05 00:20:14 +0200
committerGuenter Roeck <linux@roeck-us.net>2021-08-17 14:54:25 -0700
commitbd56c1e9603a4c645fcafdef8df9b2b04125d406 (patch)
tree712cf55092bd4acbd1cdf173b6b305c5757e40ec /drivers/hwmon
parent02c9dce4df8dd23e67dac1074be732c65c0e67d8 (diff)
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: Linus Walleij <linus.walleij@linaro.org> Link: https://lore.kernel.org/r/20210704222014.12058-1-linus.walleij@linaro.org Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Diffstat (limited to 'drivers/hwmon')
-rw-r--r--drivers/hwmon/ntc_thermistor.c20
1 files changed, 11 insertions, 9 deletions
diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
index 18fd6f12ca16..cf26c44f2b88 100644
--- a/drivers/hwmon/ntc_thermistor.c
+++ b/drivers/hwmon/ntc_thermistor.c
@@ -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;
}