hwmon: (adt7473) Fix voltage conversion routines

Fix voltage conversion routines. Based on an earlier patch from
Paulius Zaleckas.

According to the datasheet voltage is scaled with resistors and
value 192 is nominal voltage. 0 is 0V.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Paulius Zaleckas <paulius.zaleckas@teltonika.lt>
Cc: Darrick J. Wong <djwong@us.ibm.com>

drivers/hwmon/adt7473.c

@@ -319,35 +319,24 @@ static struct adt7473_data *adt7473_update_device(struct device *dev)
 }
 
 /*
- * On this chip, voltages are given as a count of steps between a minimum
- * and maximum voltage, not a direct voltage.
+ * Conversions
  */
-static const int volt_convert_table[][2] = {
-	{2997, 3},
-	{4395, 4},
+
+/* IN are scaled acording to built-in resistors */
+static const int adt7473_scaling[] = {  /* .001 Volts */
+	2250, 3300
 };
+#define SCALE(val, from, to)	(((val) * (to) + ((from) / 2)) / (from))
 
 static int decode_volt(int volt_index, u8 raw)
 {
-	int cmax = volt_convert_table[volt_index][0];
-	int cmin = volt_convert_table[volt_index][1];
-	return ((raw * (cmax - cmin)) / 255) + cmin;
+	return SCALE(raw, 192, adt7473_scaling[volt_index]);
 }
 
 static u8 encode_volt(int volt_index, int cooked)
 {
-	int cmax = volt_convert_table[volt_index][0];
-	int cmin = volt_convert_table[volt_index][1];
-	u8 x;
-
-	if (cooked > cmax)
-		cooked = cmax;
-	else if (cooked < cmin)
-		cooked = cmin;
-
-	x = ((cooked - cmin) * 255) / (cmax - cmin);
-
-	return x;
+	int raw = SCALE(cooked, adt7473_scaling[volt_index], 192);
+	return SENSORS_LIMIT(raw, 0, 255);
 }
 
 static ssize_t show_volt_min(struct device *dev,