From e4879e28abd67b894fb9d2db0afd08f1945670ba Mon Sep 17 00:00:00 2001
From: Jean Delvare <khali@linux-fr.org>
Date: Mon, 30 Mar 2009 21:46:40 +0200
Subject: [PATCH] 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>
---
drivers/hwmon/ds1621.c | 15 +++++++++------
1 file 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);
--
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