hwmon: (lm92) Improve auto-detection accuracy

Checking three configuration register bits and the manufacturer ID
register to auto-detect LM92 is a bit vague. Repeat twice on replicated
register addresses to improve detection accuracy.  Check the manufacturer
ID first and bail out immediately without reading the other register if
there is a mismatch to reduce the number of i2c transfers needed in that
case. Also explicitly test for an error from reading the configuration
register to avoid potential situations where the returned error masked
against 0xe0 is 0.

While at it, drop "lm92: Found National Semiconductor LM92 chip" detection
noise.
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/lm92.c

@@ -272,20 +272,28 @@ static int lm92_detect(struct i2c_client *new_client,
 		       struct i2c_board_info *info)
 {
 	struct i2c_adapter *adapter = new_client->adapter;
-	u8 config;
-	u16 man_id;
+	u8 config_addr = LM92_REG_CONFIG;
+	u8 man_id_addr = LM92_REG_MAN_ID;
+	int i, regval;
 
 	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA
 					    | I2C_FUNC_SMBUS_WORD_DATA))
 		return -ENODEV;
 
-	config = i2c_smbus_read_byte_data(new_client, LM92_REG_CONFIG);
-	man_id = i2c_smbus_read_word_data(new_client, LM92_REG_MAN_ID);
-
-	if ((config & 0xe0) == 0x00 && man_id == 0x0180)
-		pr_info("lm92: Found National Semiconductor LM92 chip\n");
-	else
+	/*
+	 * Register values repeat with multiples of 8.
+	 * Read twice to improve detection accuracy.
+	 */
+	for (i = 0; i < 2; i++) {
+		regval = i2c_smbus_read_word_data(new_client, man_id_addr);
+		if (regval != 0x0180)
 			return -ENODEV;
+		regval = i2c_smbus_read_byte_data(new_client, config_addr);
+		if (regval < 0 || (regval & 0xe0))
+			return -ENODEV;
+		config_addr += 8;
+		man_id_addr += 8;
+	}
 
 	strscpy(info->type, "lm92", I2C_NAME_SIZE);