On 7/4/21 9:14 AM, Jonathan Cameron wrote:
On Sat, 3 Jul 2021 20:01:31 +0200
Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
The kernel has a helper function for linear interpolation so
use it. It incidentally makes the code easier to read as well.
Cc: Peter Rosin <peda@xxxxxxxxxx>
Cc: Chris Lesiak <chris.lesiak@xxxxxxxxx>
Cc: linux-iio@xxxxxxxxxxxxxxx
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Potential precision problem because the multiplication by 1000 is now done
post division whereas before it was before it?
I'm only eyeballing the code so no idea if it makes a practical difference.
I think so, since the code now only reports temperatures in full degrees C
which wasn't the case earlier. That should be easy to fix though by
passing data->comp[low].temp_c * 1000 and data->comp[high].temp_c * 1000
as parameters to fixp_linear_interpolate().
Also, the if/else in get_temp_mc() seems now unnecessary since
fixp_linear_interpolate() effectively does the same checks.
Guenter
---
drivers/hwmon/ntc_thermistor.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
index 8587189c7f15..61bd0e074ec9 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>
@@ -557,10 +558,12 @@ static int get_temp_mc(struct ntc_data *data, unsigned int ohm)
/* 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);
+ temp = fixp_linear_interpolate(data->comp[low].ohm,
+ data->comp[low].temp_c,
+ data->comp[high].ohm,
+ data->comp[high].temp_c,
+ ohm);
+ temp *= 1000;
}
return temp;
}
