hwmon: (lm90) Fix handling of hysteresis value

There are several problems in the way the hysteresis value is handled
by the lm90 driver:

* In show_temphyst(), specific handling of the MAX6646 is missing, so
  the hysteresis is reported incorrectly if the critical temperature
  is over 127 degrees C.
* In set_temphyst(), the new hysteresis register value is written to
  the chip but data->temp_hyst isn't updated accordingly, so there is
  a short period of time (up to 2 seconds) where the old hystereris
  value will be returned while the new one is already active.
* In set_temphyst(), the critical temperature which is used as a base
  to compute the value of the hysteresis register lacks
  device-specific handling. As a result, the value of the hysteresis
  register might be incorrect for the ADT7461 and MAX6646 chips.

Fix these 3 bugs.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: Nate Case <ncase@xes-inc.com>

1 files changed, 12 insertions, 3 deletions

diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
index 3edeebc0b835..6242e72a82c1 100644
--- a/drivers/hwmon/lm90.c
+++ b/drivers/hwmon/lm90.c
@@ -461,6 +461,8 @@ static ssize_t show_temphyst(struct device *dev, struct device_attribute *devatt
 
         if (data->kind == adt7461)
                 temp = temp_from_u8_adt7461(data, data->temp8[attr->index]);
+        else if (data->kind == max6646)
+                temp = temp_from_u8(data->temp8[attr->index]);
         else
                 temp = temp_from_s8(data->temp8[attr->index]);
 
@@ -473,12 +475,19 @@ static ssize_t set_temphyst(struct device *dev, struct device_attribute *dummy,
         struct i2c_client *client = to_i2c_client(dev);
         struct lm90_data *data = i2c_get_clientdata(client);
         long val = simple_strtol(buf, NULL, 10);
-        long hyst;
+        int temp;
 
         mutex_lock(&data->update_lock);
-        hyst = temp_from_s8(data->temp8[2]) - val;
+        if (data->kind == adt7461)
+                temp = temp_from_u8_adt7461(data, data->temp8[2]);
+        else if (data->kind == max6646)
+                temp = temp_from_u8(data->temp8[2]);
+        else
+                temp = temp_from_s8(data->temp8[2]);
+
+        data->temp_hyst = hyst_to_reg(temp - val);
         i2c_smbus_write_byte_data(client, LM90_REG_W_TCRIT_HYST,
-                                  hyst_to_reg(hyst));
+                                  data->temp_hyst);
         mutex_unlock(&data->update_lock);
         return count;
 }