hwmon: (adm9240) handle temperature readings below 0

Unlike the temperature thresholds the temperature data is a 9-bit signed
value. This allows and additional 0.5 degrees of precision on the
reading but makes handling negative values slightly harder. In order to
have sign-extension applied correctly the 9-bit value is stored in the
upper bits of a signed 16-bit value. When presenting this in sysfs the
value is shifted and scaled appropriately.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/adm9240.c

@@ -194,10 +194,10 @@ static struct adm9240_data *adm9240_update_device(struct device *dev)
 		 * 0.5'C per two measurement cycles thus ignore possible
 		 * but unlikely aliasing error on lsb reading. --Grant
 		 */
-		data->temp = ((i2c_smbus_read_byte_data(client,
+		data->temp = (i2c_smbus_read_byte_data(client,
 					ADM9240_REG_TEMP) << 8) |
 					i2c_smbus_read_byte_data(client,
-					ADM9240_REG_TEMP_CONF)) / 128;
+					ADM9240_REG_TEMP_CONF);
 
 		for (i = 0; i < 2; i++) { /* read fans */
 			data->fan[i] = i2c_smbus_read_byte_data(client,
@@ -263,7 +263,7 @@ static ssize_t show_temp(struct device *dev, struct device_attribute *dummy,
 		char *buf)
 {
 	struct adm9240_data *data = adm9240_update_device(dev);
-	return sprintf(buf, "%d\n", data->temp * 500); /* 9-bit value */
+	return sprintf(buf, "%d\n", data->temp / 128 * 500); /* 9-bit value */
 }
 
 static ssize_t show_max(struct device *dev, struct device_attribute *devattr,