+#define FACTOR0 10000000
+#define FACTOR1 15976
+#define FACTOR2 4297157
+
+int raw_to_celsius(unsigned int raw, unsigned int raw_25c, unsigned int raw_hot,
+ unsigned int hot_temp)
+{
+ int temperature;
+
+ if (raw_hot != 0 && hot_temp != 0) {
+ unsigned int raw_n40c, ratio;
+
+ ratio = ((raw_25c - raw_hot) * 100) / (hot_temp - 25);
+ raw_n40c = raw_25c + (13 * ratio) / 20;
+ if (raw <= raw_n40c)
+ temperature = (raw_n40c - raw) * 100 / ratio - 40;
+ else
+ temperature = TEMPERATURE_MIN;
+ } else {
+ u64 temp64 = FACTOR0;
+ unsigned int c1, c2;
+ /*
+ * Derived from linear interpolation:
+ * slope = 0.4297157 - (0.0015976 * 25C fuse)
+ * slope = (FACTOR2 - FACTOR1 * n1) / FACTOR0
+ * (Nmeas - n1) / (Tmeas - t1) = slope
+ * We want to reduce this down to the minimum computation necessary
+ * for each temperature read. Also, we want Tmeas in millicelsius
+ * and we don't want to lose precision from integer division. So...
+ * Tmeas = (Nmeas - n1) / slope + t1
+ * milli_Tmeas = 1000 * (Nmeas - n1) / slope + 1000 * t1
+ * milli_Tmeas = -1000 * (n1 - Nmeas) / slope + 1000 * t1
+ * Let constant c1 = (-1000 / slope)
+ * milli_Tmeas = (n1 - Nmeas) * c1 + 1000 * t1
+ * Let constant c2 = n1 *c1 + 1000 * t1
+ * milli_Tmeas = c2 - Nmeas * c1
+ */
+ temp64 *= 1000;
+ do_div(temp64, FACTOR1 * raw_25c - FACTOR2);
+ c1 = temp64;
+ c2 = raw_25c * c1 + 1000 * 25;
+ temperature = (c2 - raw * c1) / 1000;
+ }
+ return temperature;
+}
+