hwmon: (lm95245) Make temp2_crit_hyst read-only

The hysteresis register is shared among both temperature sensors.
This means changing one also affects the other. To avoid confusion,
established way to express this is to make only the first instance writable
and keep all other instances as read-only. Otherwise users may be
confused that changing the second writable value also affects the first,
while it is more obvious that a writable value may affect a different
read-only value.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Jean Delvare <jdelvare@suse.de>

Documentation/hwmon/lm95245

@@ -24,8 +24,12 @@ is given within a range of -127 to +127.875 degrees. Remote temperatures are
 given within a range of -127 to +255 degrees. Resolution depends on
 temperature input and range.
 
-Each sensor has its own critical limit, but the hysteresis is common to all
-two channels.
+Each sensor has its own critical limit. Additionally, there is a relative
+hysteresis value common to both critical limits. To make life easier to
+user-space applications, two absolute values are exported, one for each
+channel, but these values are of course linked. Only the local hysteresis
+can be set from user-space, and the same delta applies to the remote
+hysteresis.
 
 The lm95245 driver can change its update interval to a fixed set of values.
 It will round up to the next selectable interval. See the datasheet for exact

drivers/hwmon/lm95245.c

@@ -395,8 +395,7 @@ static SENSOR_DEVICE_ATTR(temp1_crit_alarm, S_IRUGO, show_alarm, NULL,
 static SENSOR_DEVICE_ATTR(temp2_input, S_IRUGO, show_input, NULL, 2);
 static SENSOR_DEVICE_ATTR(temp2_crit, S_IWUSR | S_IRUGO, show_limit,
 		set_limit, 7);
-static SENSOR_DEVICE_ATTR(temp2_crit_hyst, S_IWUSR | S_IRUGO, show_crit_hyst,
-		set_crit_hyst, 7);
+static SENSOR_DEVICE_ATTR(temp2_crit_hyst, S_IRUGO, show_crit_hyst, NULL, 7);
 static SENSOR_DEVICE_ATTR(temp2_crit_alarm, S_IRUGO, show_alarm, NULL,
 		STATUS1_RTCRIT);
 static SENSOR_DEVICE_ATTR(temp2_type, S_IWUSR | S_IRUGO, show_type,