hwmon: (ds1621) Avoid unneeded register access

Register access over SMBus isn't cheap, so avoid register access where
possible:
* Only write back the configuration register if it changed.
* Don't refresh the register cache when we don't have to.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 9 insertions, 6 deletions

diff --git a/drivers/hwmon/ds1621.c b/drivers/hwmon/ds1621.c
index fe160c54b959..53f88f511816 100644
--- a/drivers/hwmon/ds1621.c
+++ b/drivers/hwmon/ds1621.c
@@ -101,17 +101,20 @@ static int ds1621_write_temp(struct i2c_client *client, u8 reg, u16 value)
 
 static void ds1621_init_client(struct i2c_client *client)
 {
-        int reg = i2c_smbus_read_byte_data(client, DS1621_REG_CONF);
+        u8 conf, new_conf;
+
+        new_conf = conf = i2c_smbus_read_byte_data(client, DS1621_REG_CONF);
         /* switch to continuous conversion mode */
-        reg &= ~ DS1621_REG_CONFIG_1SHOT;
+        new_conf &= ~DS1621_REG_CONFIG_1SHOT;
 
         /* setup output polarity */
         if (polarity == 0)
-                reg &= ~DS1621_REG_CONFIG_POLARITY;
+                new_conf &= ~DS1621_REG_CONFIG_POLARITY;
         else if (polarity == 1)
-                reg |= DS1621_REG_CONFIG_POLARITY;
+                new_conf |= DS1621_REG_CONFIG_POLARITY;
         
-        i2c_smbus_write_byte_data(client, DS1621_REG_CONF, reg);
+        if (conf != new_conf)
+                i2c_smbus_write_byte_data(client, DS1621_REG_CONF, new_conf);
         
         /* start conversion */
         i2c_smbus_write_byte(client, DS1621_COM_START);
@@ -170,7 +173,7 @@ static ssize_t set_temp(struct device *dev, struct device_attribute *da,
 {
         struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
         struct i2c_client *client = to_i2c_client(dev);
-        struct ds1621_data *data = ds1621_update_client(dev);
+        struct ds1621_data *data = i2c_get_clientdata(client);
         u16 val = LM75_TEMP_TO_REG(simple_strtol(buf, NULL, 10));
 
         mutex_lock(&data->update_lock);