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@xxxxxxxxxx>
Cc: Chris Lesiak <chris.lesiak@xxxxxxxxx>
Cc: linux-iio@xxxxxxxxxxxxxxx
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
ChangeLog v1->v2:
- Drop the check for low == high as the linear interpolation
library function does this for us.
- Multiply the temperatures in the table with 1000 *before*
interpolating instead of *after* so we increase precision
in the interpolation.
---
drivers/hwmon/ntc_thermistor.c | 20 +++++++++++---------
1 file changed, 11 insertions(+), 9 deletions(-)
diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
index 8587189c7f15..4c26db6738f9 100644
--- a/drivers/hwmon/ntc_thermistor.c
+++ b/drivers/hwmon/ntc_thermistor.c
@@ -14,6 +14,7 @@
#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>
@@ -553,15 +554,16 @@ 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;
}
--
2.31.1
