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hwmon: (lm75) Speed up detection 

Make the LM75/LM75A device detection faster:

* Don't read the current temperature value when we don't use it.
* Check for unused bits in the configuration register as soon as we
  have read its value.
* Don't use word reads, not all devices support this, and some which
  don't misbehave when you try.
* Check for cycling register values every 40 register addresses
  instead of every 8, it's 5 times faster and just as efficient.

Some of these improvements come straight from the user-space
sensors-detect script, so both detection routines are in line now.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Len Sorensen <lsorense@csclub.uwaterloo.ca>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>
This commit is contained in:
Jean Delvare 2011-03-21 17:59:36 +01:00 committed by Jean Delvare
parent 05e82fe40f
commit e76f67b5ba
1 changed files with 19 additions and 21 deletions
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40
drivers/hwmon/lm75.c
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@ -240,7 +240,7 @@ static int lm75_detect(struct i2c_client *new_client,
{
struct i2c_adapter *adapter = new_client->adapter;
int i;
int cur, conf, hyst, os;
int conf, hyst, os;
bool is_lm75a = 0;
if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
@ -261,8 +261,10 @@ static int lm75_detect(struct i2c_client *new_client,
register 7, and unused registers return 0xff rather than the
last read value. */
cur = i2c_smbus_read_word_data(new_client, 0);
/* Unused bits */
conf = i2c_smbus_read_byte_data(new_client, 1);
if (conf & 0xe0)
return -ENODEV;
/* First check for LM75A */
if (i2c_smbus_read_byte_data(new_client, 7) == LM75A_ID) {
@ -273,33 +275,29 @@ static int lm75_detect(struct i2c_client *new_client,
|| i2c_smbus_read_byte_data(new_client, 6) != 0xff)
return -ENODEV;
is_lm75a = 1;
hyst = i2c_smbus_read_word_data(new_client, 2);
os = i2c_smbus_read_word_data(new_client, 3);
hyst = i2c_smbus_read_byte_data(new_client, 2);
os = i2c_smbus_read_byte_data(new_client, 3);
} else { /* Traditional style LM75 detection */
/* Unused addresses */
hyst = i2c_smbus_read_word_data(new_client, 2);
if (i2c_smbus_read_word_data(new_client, 4) != hyst
|| i2c_smbus_read_word_data(new_client, 5) != hyst
|| i2c_smbus_read_word_data(new_client, 6) != hyst
|| i2c_smbus_read_word_data(new_client, 7) != hyst)
hyst = i2c_smbus_read_byte_data(new_client, 2);
if (i2c_smbus_read_byte_data(new_client, 4) != hyst
|| i2c_smbus_read_byte_data(new_client, 5) != hyst
|| i2c_smbus_read_byte_data(new_client, 6) != hyst
|| i2c_smbus_read_byte_data(new_client, 7) != hyst)
return -ENODEV;
os = i2c_smbus_read_word_data(new_client, 3);
if (i2c_smbus_read_word_data(new_client, 4) != os
|| i2c_smbus_read_word_data(new_client, 5) != os
|| i2c_smbus_read_word_data(new_client, 6) != os
|| i2c_smbus_read_word_data(new_client, 7) != os)
os = i2c_smbus_read_byte_data(new_client, 3);
if (i2c_smbus_read_byte_data(new_client, 4) != os
|| i2c_smbus_read_byte_data(new_client, 5) != os
|| i2c_smbus_read_byte_data(new_client, 6) != os
|| i2c_smbus_read_byte_data(new_client, 7) != os)
return -ENODEV;
}
/* Unused bits */
if (conf & 0xe0)
return -ENODEV;
/* Addresses cycling */
for (i = 8; i < 0xff; i += 8) {
for (i = 8; i <= 248; i += 40) {
if (i2c_smbus_read_byte_data(new_client, i + 1) != conf
|| i2c_smbus_read_word_data(new_client, i + 2) != hyst
|| i2c_smbus_read_word_data(new_client, i + 3) != os)
|| i2c_smbus_read_byte_data(new_client, i + 2) != hyst
|| i2c_smbus_read_byte_data(new_client, i + 3) != os)
return -ENODEV;
if (is_lm75a && i2c_smbus_read_byte_data(new_client, i + 7)
!= LM75A_ID)