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>

diff --git a/drivers/hwmon/adm9240.c b/drivers/hwmon/adm9240.c
index 98114ce..2fe1828 100644 (file)
--- a/drivers/hwmon/adm9240.c
+++ b/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,