adt7470: observe the number of temperature sensors to shorten update time

The adt7470 driver currently assumes that 1s is the proper time to wait to
read all temperature sensors. However, the correct time is 200ms *
number_of_sensors. This patch sets the default time to provide for 10
sensors and then lowers it based on the number of sensor inputs that have
nozero values.

Signed-off-by: Darrick J. Wong <[e-mail]>
Cc: Jean Delvare <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/hwmon/adt7470.c

···
 /* How often do we reread sensor limit values? (In jiffies) */
 #define LIMIT_REFRESH_INTERVAL	(60 * HZ)
 
-/* sleep 1s while gathering temperature data */
-#define TEMP_COLLECTION_TIME	1000
+/* Wait at least 200ms per sensor for 10 sensors */
+#define TEMP_COLLECTION_TIME	2000
 
 /* datasheet says to divide this number by the fan reading to get fan rpm */
 #define FAN_PERIOD_TO_RPM(x)	((90000 * 60) / (x))
···
 	char			limits_valid;
 	unsigned long		sensors_last_updated;	/* In jiffies */
 	unsigned long		limits_last_updated;	/* In jiffies */
+
+	int			num_temp_sensors;	/* -1 = probe */
 
 	s8			temp[ADT7470_TEMP_COUNT];
 	s8			temp_min[ADT7470_TEMP_COUNT];
···
 	cfg |= 0x80;
 	i2c_smbus_write_byte_data(client, ADT7470_REG_CFG, cfg);
 
-	/*
-	 * Delay is 200ms * number of tmp05 sensors.  Too bad
-	 * there's no way to figure out how many are connected.
-	 * For now, assume 1s will work.
-	 */
-	msleep(TEMP_COLLECTION_TIME);
+	/* Delay is 200ms * number of temp sensors. */
+	msleep((data->num_temp_sensors >= 0 ?
+		data->num_temp_sensors * 200 :
+		TEMP_COLLECTION_TIME));
 
 	/* done reading temperature sensors */
 	cfg = i2c_smbus_read_byte_data(client, ADT7470_REG_CFG);
···
 	for (i = 0; i < ADT7470_TEMP_COUNT; i++)
 		data->temp[i] = i2c_smbus_read_byte_data(client,
 						ADT7470_TEMP_REG(i));
+
+	/* Figure out the number of temp sensors */
+	if (data->num_temp_sensors < 0)
+		for (i = 0; i < ADT7470_TEMP_COUNT; i++)
+			if (data->temp[i])
+				data->num_temp_sensors = i + 1;
 
 	for (i = 0; i < ADT7470_FAN_COUNT; i++)
 		data->fan[i] = adt7470_read_word_data(client,
···
 out:
 	mutex_unlock(&data->lock);
 	return data;
+}
+
+static ssize_t show_num_temp_sensors(struct device *dev,
+				     struct device_attribute *devattr,
+				     char *buf)
+{
+	struct adt7470_data *data = adt7470_update_device(dev);
+	return sprintf(buf, "%d\n", data->num_temp_sensors);
+}
+
+static ssize_t set_num_temp_sensors(struct device *dev,
+				    struct device_attribute *devattr,
+				    const char *buf,
+				    size_t count)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct adt7470_data *data = i2c_get_clientdata(client);
+	long temp;
+
+	if (strict_strtol(buf, 10, &temp))
+		return -EINVAL;
+
+	temp = SENSORS_LIMIT(temp, -1, 10);
+
+	mutex_lock(&data->lock);
+	data->num_temp_sensors = temp;
+	mutex_unlock(&data->lock);
+
+	return count;
 }
 
 static ssize_t show_temp_min(struct device *dev,
···
 }
 
 static DEVICE_ATTR(alarm_mask, S_IRUGO, show_alarm_mask, NULL);
+static DEVICE_ATTR(num_temp_sensors, S_IWUSR | S_IRUGO, show_num_temp_sensors,
+		   set_num_temp_sensors);
 
 static SENSOR_DEVICE_ATTR(temp1_max, S_IWUSR | S_IRUGO, show_temp_max,
 		    set_temp_max, 0);
···
 static struct attribute *adt7470_attr[] =
 {
 	&dev_attr_alarm_mask.attr,
+	&dev_attr_num_temp_sensors.attr,
 	&sensor_dev_attr_temp1_max.dev_attr.attr,
 	&sensor_dev_attr_temp2_max.dev_attr.attr,
 	&sensor_dev_attr_temp3_max.dev_attr.attr,
···
 		err = -ENOMEM;
 		goto exit;
 	}
+
+	data->num_temp_sensors = -1;
 
 	i2c_set_clientdata(client, data);
 	mutex_init(&data->lock);