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>

1 files changed, 19 insertions, 21 deletions

diff --git a/drivers/hwmon/lm75.c b/drivers/hwmon/lm75.c
index 638dd0586e3f..ef902d5d06ab 100644
--- 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)