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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>
This commit is contained in:
Jean Delvare 2009-03-30 21:46:40 +02:00
parent 594592dc6f
commit e4879e28ab
1 changed files with 9 additions and 6 deletions
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15
drivers/hwmon/ds1621.c
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@ -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);