hwmon: (ds1621) Fix temperature rounding operations

Commit "hwmon: (ds1621) Add ds1721 chip support" broke rounding
for chips or configurations with less than 12 bit resolution.

Tested-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/ds1621.c b/drivers/hwmon/ds1621.c
index 591758bb629f0888b55920583c92c406b7e5dfd9..a26ba7a17c2be824797c728bc415cc2e3fd49bdb 100644 (file)
--- a/drivers/hwmon/ds1621.c
+++ b/drivers/hwmon/ds1621.c
@@ -128,6 +128,8 @@ struct ds1621_data {
 
        u16 temp[3];                    /* Register values, word */
        u8 conf;                        /* Register encoding, combined */
+       u8 zbits;                       /* Resolution encoded as number of
+                                        * zero bits */
        u16 update_interval;            /* Conversion rate in milliseconds */
 };
 
@@ -139,16 +141,14 @@ static inline int DS1621_TEMP_FROM_REG(u16 reg)
 /*
  * TEMP: 0.001C/bit (-55C to +125C)
  * REG:
- *  - 1621, 1625: 0.5C/bit
- *  - 1631, 1721, 1731: 0.0625C/bit
- * Assume highest resolution and let the bits fall where they may..
+ *  - 1621, 1625: 0.5C/bit, 7 zero-bits
+ *  - 1631, 1721, 1731: 0.0625C/bit, 4 zero-bits
  */
-static inline u16 DS1621_TEMP_TO_REG(long temp)
+static inline u16 DS1621_TEMP_TO_REG(long temp, u8 zbits)
 {
-       int ntemp = clamp_val(temp, DS1621_TEMP_MIN, DS1621_TEMP_MAX);
-       ntemp += (ntemp < 0 ? -31 : 31);
-       ntemp = DIV_ROUND_CLOSEST(ntemp * 10, 625) << 4;
-       return (u16)ntemp;
+       temp = clamp_val(temp, DS1621_TEMP_MIN, DS1621_TEMP_MAX);
+       temp = DIV_ROUND_CLOSEST(temp * (1 << (8 - zbits)), 1000) << zbits;
+       return temp;
 }
 
 static void ds1621_init_client(struct i2c_client *client)
@@ -172,6 +172,7 @@ static void ds1621_init_client(struct i2c_client *client)
        switch (data->kind) {
        case ds1625:
                data->update_interval = DS1625_CONVERSION_MAX;
+               data->zbits = 7;
                sreg = DS1621_COM_START;
                break;
        case ds1631:
@@ -180,10 +181,12 @@ static void ds1621_init_client(struct i2c_client *client)
                resol = (new_conf & DS1621_REG_CONFIG_RESOL) >>
                         DS1621_REG_CONFIG_RESOL_SHIFT;
                data->update_interval = ds1721_convrates[resol];
+               data->zbits = 7 - resol;
                sreg = DS1721_COM_START;
                break;
        default:
                data->update_interval = DS1621_CONVERSION_MAX;
+               data->zbits = 7;
                sreg = DS1621_COM_START;
                break;
        }
@@ -254,7 +257,7 @@ static ssize_t set_temp(struct device *dev, struct device_attribute *da,
                return err;
 
        mutex_lock(&data->update_lock);
-       data->temp[attr->index] = DS1621_TEMP_TO_REG(val);
+       data->temp[attr->index] = DS1621_TEMP_TO_REG(val, data->zbits);
        i2c_smbus_write_word_swapped(client, DS1621_REG_TEMP[attr->index],
                                     data->temp[attr->index]);
        mutex_unlock(&data->update_lock);