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>

diff --git a/drivers/hwmon/lm75.c b/drivers/hwmon/lm75.c
index 638dd0586e3f4f51360ab2124f4ef7ee9643db2d..ef902d5d06ab9f98e610f63ed0ee709eb0f66b87 100644 (file)
--- a/drivers/hwmon/lm75.c
+++ b/drivers/hwmon/lm75.c
@@ -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)