hwmon: (ntc_thermistor) return error instead of clipping on OOB

When the ntc is reading Out Of Bounds instead of clipping to the nearest
limit (min/max) return -ENODATA. This prevents malfunctioning sensors
from sending a device into a shutdown loop due to a critical trip.

This implementation will only work for ntc type thermistors if a ptc
type is to be implemented the min/max ohm calculation must be adjusted
to take that into account.

Signed-off-by: Maud Spierings <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Guenter Roeck <[email protected]>

Author: SpieringsAE

drivers/hwmon/ntc_thermistor.c

@@ -387,12 +387,9 @@ static int get_ohm_of_thermistor(struct ntc_data *data, unsigned int uv)
 	puo = data->pullup_ohm;
 	pdo = data->pulldown_ohm;
 
-	if (uv == 0)
-		return (data->connect == NTC_CONNECTED_POSITIVE) ?
-			INT_MAX : 0;
-	if (uv >= puv)
-		return (data->connect == NTC_CONNECTED_POSITIVE) ?
-			0 : INT_MAX;
+	/* faulty adc value */
+	if (uv == 0 || uv >= puv)
+		return -ENODATA;
 
 	if (data->connect == NTC_CONNECTED_POSITIVE && puo == 0)
 		n = div_u64(pdo * (puv - uv), uv);
@@ -404,8 +401,10 @@ static int get_ohm_of_thermistor(struct ntc_data *data, unsigned int uv)
 	else
 		n = div64_u64_safe(pdo * puo * uv, pdo * (puv - uv) - puo * uv);
 
-	if (n > INT_MAX)
-		n = INT_MAX;
+	/* sensor out of bounds */
+	if (n > data->comp[0].ohm || n < data->comp[data->n_comp - 1].ohm)
+		return -ENODATA;
+
 	return n;
 }