hwmon: (adm1031) Allow setting update rate

Based on earlier work by Ira W. Snyder.

The adm1031 chip is capable of using a runtime configurable sampling rate,
using the fan filter register. Add support for reading and setting the
update rate via sysfs.

Signed-off-by: Jean Delvare <[e-mail]>
Acked-by: Ira W. Snyder <[e-mail]>

drivers/hwmon/adm1031.c

···
 #define ADM1031_REG_FAN_DIV(nr)		(0x20 + (nr))
 #define ADM1031_REG_PWM			(0x22)
 #define ADM1031_REG_FAN_MIN(nr)		(0x10 + (nr))
+#define ADM1031_REG_FAN_FILTER		(0x23)
 
 #define ADM1031_REG_TEMP_OFFSET(nr)	(0x0d + (nr))
 #define ADM1031_REG_TEMP_MAX(nr)	(0x14 + 4 * (nr))
···
 #define ADM1031_CONF2_TACH2_ENABLE	0x08
 #define ADM1031_CONF2_TEMP_ENABLE(chan)	(0x10 << (chan))
 
+#define ADM1031_UPDATE_RATE_MASK	0x1c
+#define ADM1031_UPDATE_RATE_SHIFT	2
+
 /* Addresses to scan */
 static const unsigned short normal_i2c[] = { 0x2c, 0x2d, 0x2e, I2C_CLIENT_END };
 
···
 	int chip_type;
 	char valid;		/* !=0 if following fields are valid */
 	unsigned long last_updated;	/* In jiffies */
+	unsigned int update_rate;	/* In milliseconds */
 	/* The chan_select_table contains the possible configurations for
 	 * auto fan control.
 	 */
···
 static SENSOR_DEVICE_ATTR(temp3_fault, S_IRUGO, show_alarm, NULL, 13);
 static SENSOR_DEVICE_ATTR(temp1_crit_alarm, S_IRUGO, show_alarm, NULL, 14);
 
+/* Update Rate */
+static const unsigned int update_rates[] = {
+	16000, 8000, 4000, 2000, 1000, 500, 250, 125,
+};
+
+static ssize_t show_update_rate(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct adm1031_data *data = i2c_get_clientdata(client);
+
+	return sprintf(buf, "%u\n", data->update_rate);
+}
+
+static ssize_t set_update_rate(struct device *dev,
+			       struct device_attribute *attr,
+			       const char *buf, size_t count)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct adm1031_data *data = i2c_get_clientdata(client);
+	unsigned long val;
+	int i, err;
+	u8 reg;
+
+	err = strict_strtoul(buf, 10, &val);
+	if (err)
+		return err;
+
+	/* find the nearest update rate from the table */
+	for (i = 0; i < ARRAY_SIZE(update_rates) - 1; i++) {
+		if (val >= update_rates[i])
+			break;
+	}
+	/* if not found, we point to the last entry (lowest update rate) */
+
+	/* set the new update rate while preserving other settings */
+	reg = adm1031_read_value(client, ADM1031_REG_FAN_FILTER);
+	reg &= ~ADM1031_UPDATE_RATE_MASK;
+	reg |= i << ADM1031_UPDATE_RATE_SHIFT;
+	adm1031_write_value(client, ADM1031_REG_FAN_FILTER, reg);
+
+	mutex_lock(&data->update_lock);
+	data->update_rate = update_rates[i];
+	mutex_unlock(&data->update_lock);
+
+	return count;
+}
+
+static DEVICE_ATTR(update_rate, S_IRUGO | S_IWUSR, show_update_rate,
+		   set_update_rate);
+
 static struct attribute *adm1031_attributes[] = {
 	&sensor_dev_attr_fan1_input.dev_attr.attr,
 	&sensor_dev_attr_fan1_div.dev_attr.attr,
···
 
 	&sensor_dev_attr_auto_fan1_min_pwm.dev_attr.attr,
 
+	&dev_attr_update_rate.attr,
 	&dev_attr_alarms.attr,
 
 	NULL
···
 {
 	unsigned int read_val;
 	unsigned int mask;
+	int i;
 	struct adm1031_data *data = i2c_get_clientdata(client);
 
 	mask = (ADM1031_CONF2_PWM1_ENABLE | ADM1031_CONF2_TACH1_ENABLE);
···
 				ADM1031_CONF1_MONITOR_ENABLE);
 	}
 
+	/* Read the chip's update rate */
+	mask = ADM1031_UPDATE_RATE_MASK;
+	read_val = adm1031_read_value(client, ADM1031_REG_FAN_FILTER);
+	i = (read_val & mask) >> ADM1031_UPDATE_RATE_SHIFT;
+	data->update_rate = update_rates[i];
 }
 
 static struct adm1031_data *adm1031_update_device(struct device *dev)
 {
 	struct i2c_client *client = to_i2c_client(dev);
 	struct adm1031_data *data = i2c_get_clientdata(client);
+	unsigned long next_update;
 	int chan;
 
 	mutex_lock(&data->update_lock);
 
-	if (time_after(jiffies, data->last_updated + HZ + HZ / 2)
-	    || !data->valid) {
+	next_update = data->last_updated + msecs_to_jiffies(data->update_rate);
+	if (time_after(jiffies, next_update) || !data->valid) {
 
 		dev_dbg(&client->dev, "Starting adm1031 update\n");
 		for (chan = 0;