adt7470: fix pwm at a certain level during temperature sensor scan

In the small window that it takes to read the temperature sensors, the pwm
outputs momentarily drop to 0. This causes a noticeable hiccup in fan
speed, which is slightly annoying. The solution is to manually program
the pwm output with whatever the automatic value is and then shift the
fans to manual control while reading temperatures. Once that is done, put
the fans back to whatever mode of control was there before.

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

···
 #define ADT7470_REG_PWM12_CFG			0x68
 #define		ADT7470_PWM2_AUTO_MASK		0x40
 #define		ADT7470_PWM1_AUTO_MASK		0x80
+#define		ADT7470_PWM_AUTO_MASK		0xC0
 #define ADT7470_REG_PWM34_CFG			0x69
 #define		ADT7470_PWM3_AUTO_MASK		0x40
 #define		ADT7470_PWM4_AUTO_MASK		0x80
···
 	struct i2c_client *client = to_i2c_client(dev);
 	struct adt7470_data *data = i2c_get_clientdata(client);
 	unsigned long local_jiffies = jiffies;
-	u8 cfg;
+	u8 cfg, pwm[4], pwm_cfg[2];
 	int i;
 
 	mutex_lock(&data->lock);
···
 		SENSOR_REFRESH_INTERVAL)
 		&& data->sensors_valid)
 		goto no_sensor_update;
+
+	/* save pwm[1-4] config register */
+	pwm_cfg[0] = i2c_smbus_read_byte_data(client, ADT7470_REG_PWM_CFG(0));
+	pwm_cfg[1] = i2c_smbus_read_byte_data(client, ADT7470_REG_PWM_CFG(2));
+
+	/* set manual pwm to whatever it is set to now */
+	for (i = 0; i < ADT7470_FAN_COUNT; i++)
+		pwm[i] = i2c_smbus_read_byte_data(client, ADT7470_REG_PWM(i));
+
+	/* put pwm in manual mode */
+	i2c_smbus_write_byte_data(client, ADT7470_REG_PWM_CFG(0),
+		pwm_cfg[0] & ~(ADT7470_PWM_AUTO_MASK));
+	i2c_smbus_write_byte_data(client, ADT7470_REG_PWM_CFG(2),
+		pwm_cfg[1] & ~(ADT7470_PWM_AUTO_MASK));
+
+	/* write pwm control to whatever it was */
+	for (i = 0; i < ADT7470_FAN_COUNT; i++)
+		i2c_smbus_write_byte_data(client, ADT7470_REG_PWM(i), pwm[i]);
 
 	/* start reading temperature sensors */
 	cfg = i2c_smbus_read_byte_data(client, ADT7470_REG_CFG);
···
 	cfg = i2c_smbus_read_byte_data(client, ADT7470_REG_CFG);
 	cfg &= ~0x80;
 	i2c_smbus_write_byte_data(client, ADT7470_REG_CFG, cfg);
+
+	/* restore pwm[1-4] config registers */
+	i2c_smbus_write_byte_data(client, ADT7470_REG_PWM_CFG(0), pwm_cfg[0]);
+	i2c_smbus_write_byte_data(client, ADT7470_REG_PWM_CFG(2), pwm_cfg[1]);
 
 	for (i = 0; i < ADT7470_TEMP_COUNT; i++)
 		data->temp[i] = i2c_smbus_read_byte_data(client,