* [PATCH v2] hwmon: (ntc_thermistor): Use library interpolation
@ 2021-07-04 22:20 Linus Walleij
2021-07-05 17:27 ` Guenter Roeck
0 siblings, 1 reply; 2+ messages in thread
From: Linus Walleij @ 2021-07-04 22:20 UTC (permalink / raw)
To: Jean Delvare, Guenter Roeck
Cc: linux-hwmon, Linus Walleij, Peter Rosin, Chris Lesiak, linux-iio
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(-)
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] hwmon: (ntc_thermistor): Use library interpolation
2021-07-04 22:20 [PATCH v2] hwmon: (ntc_thermistor): Use library interpolation Linus Walleij
@ 2021-07-05 17:27 ` Guenter Roeck
0 siblings, 0 replies; 2+ messages in thread
From: Guenter Roeck @ 2021-07-05 17:27 UTC (permalink / raw)
To: Linus Walleij
Cc: Jean Delvare, linux-hwmon, Peter Rosin, Chris Lesiak, linux-iio
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;
> }
>
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