power: supply: ab8500: Use library interpolation

The kernel already has a static inline for linear interpolation
so use that instead of rolling our own.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/ab8500_btemp.c

@@ -27,6 +27,7 @@
 #include <linux/mfd/abx500.h>
 #include <linux/mfd/abx500/ab8500.h>
 #include <linux/iio/consumer.h>
+#include <linux/fixp-arith.h>
 
 #include "ab8500-bm.h"
 
@@ -437,8 +438,9 @@ static int ab8500_btemp_res_to_temp(struct ab8500_btemp *di,
 			i++;
 	}
 
-	return tbl[i].temp + ((tbl[i + 1].temp - tbl[i].temp) *
+	return fixp_linear_interpolate(tbl[i].resist, tbl[i].temp,
-		(res - tbl[i].resist)) / (tbl[i + 1].resist - tbl[i].resist);
+				       tbl[i + 1].resist, tbl[i + 1].temp,
+				       res);
 }
 
 /**

drivers/power/supply/ab8500_fg.c

@@ -34,6 +34,7 @@
 #include <linux/mfd/abx500/ab8500.h>
 #include <linux/iio/consumer.h>
 #include <linux/kernel.h>
+#include <linux/fixp-arith.h>
 
 #include "ab8500-bm.h"
 
@@ -56,9 +57,6 @@
 /* FG constants */
 #define BATT_OVV			0x01
 
-#define interpolate(x, x1, y1, x2, y2) \
-	((y1) + ((((y2) - (y1)) * ((x) - (x1))) / ((x2) - (x1))));
-
 /**
  * struct ab8500_fg_interrupts - ab8500 fg interrupts
  * @name:	name of the interrupt
@@ -868,11 +866,12 @@ static int ab8500_fg_volt_to_capacity(struct ab8500_fg *di, int voltage)
 	}
 
 	if ((i > 0) && (i < tbl_size)) {
-		cap = interpolate(voltage,
+		cap = fixp_linear_interpolate(
 			tbl[i].voltage,
 			tbl[i].capacity * 10,
 			tbl[i-1].voltage,
-			tbl[i-1].capacity * 10);
+			tbl[i-1].capacity * 10,
+			voltage);
 	} else if (i == 0) {
 		cap = 1000;
 	} else {
@@ -920,11 +919,12 @@ static int ab8500_fg_battery_resistance(struct ab8500_fg *di)
 	}
 
 	if ((i > 0) && (i < tbl_size)) {
-		resist = interpolate(di->bat_temp / 10,
+		resist = fixp_linear_interpolate(
 			tbl[i].temp,
 			tbl[i].resist,
 			tbl[i-1].temp,
-			tbl[i-1].resist);
+			tbl[i-1].resist,
+			di->bat_temp / 10);
 	} else if (i == 0) {
 		resist = tbl[0].resist;
 	} else {