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 <djwong@us.ibm.com>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 24 insertions, 1 deletions

diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index da6c9306ca5f..b7a442a80bde 100644
--- a/drivers/hwmon/adt7470.c
+++ b/drivers/hwmon/adt7470.c
@@ -74,6 +74,7 @@ I2C_CLIENT_INSMOD_1(adt7470);
 #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
@@ -223,7 +224,7 @@ static struct adt7470_data *adt7470_update_device(struct device *dev)
         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);
@@ -232,6 +233,24 @@ static struct adt7470_data *adt7470_update_device(struct device *dev)
                 && 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 |= 0x80;
@@ -249,6 +268,10 @@ static struct adt7470_data *adt7470_update_device(struct device *dev)
         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,
                                                 ADT7470_TEMP_REG(i));