| Message ID | 20210704222014.12058-1-linus.walleij@linaro.org (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [v2] hwmon: (ntc_thermistor): Use library interpolation | expand |
On Mon, Jul 05, 2021 at 12:20:14AM +0200, Linus Walleij wrote: > 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> Applied. Thanks, Guenter > --- > 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; > } >
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; }
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> --- 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(-)