[PATCH] lm75: add lm75b detection

[Rain Wang]

The National Semiconductor LM75B is very similar as the
LM75A, but it has no ID byte register 7, and unused registers
return 0xff rather than the last read value like LM75A.

Signed-off-by: Rain Wang <rain_wang@xxxxxxxxx>
---
 drivers/hwmon/lm75.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/lm75.c b/drivers/hwmon/lm75.c
index 5e6392294c03..a718f9eb4d72 100644
--- a/drivers/hwmon/lm75.c
+++ b/drivers/hwmon/lm75.c
@@ -760,6 +760,7 @@ static int lm75_detect(struct i2c_client *new_client,
 	int i;
 	int conf, hyst, os;
 	bool is_lm75a = 0;
+	bool is_lm75b = 0;
 
 	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
 				     I2C_FUNC_SMBUS_WORD_DATA))
@@ -780,8 +781,12 @@ static int lm75_detect(struct i2c_client *new_client,
 	 * register 7, and unused registers return 0xff rather than the
 	 * last read value.
 	 *
+	 * The National Semiconductor LM75B is very similar as the
+	 * LM75A, but it has no ID byte register 7, and unused registers 
+	 * return 0xff rather than the last read value like LM75A.
+	 *
 	 * Note that this function only detects the original National
-	 * Semiconductor LM75 and the LM75A. Clones from other vendors
+	 * Semiconductor LM75 and the LM75A/B. Clones from other vendors
 	 * aren't detected, on purpose, because they are typically never
 	 * found on PC hardware. They are found on embedded designs where
 	 * they can be instantiated explicitly so detection is not needed.
@@ -806,6 +811,13 @@ static int lm75_detect(struct i2c_client *new_client,
 		is_lm75a = 1;
 		hyst = i2c_smbus_read_byte_data(new_client, 2);
 		os = i2c_smbus_read_byte_data(new_client, 3);
+	} else if (i2c_smbus_read_byte_data(new_client, 4) == 0xff
+		 && i2c_smbus_read_byte_data(new_client, 5) == 0xff
+		 && i2c_smbus_read_byte_data(new_client, 6) == 0xff) {
+		/* LM75B detection */
+		is_lm75b = 1;
+		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_byte_data(new_client, 2);
@@ -839,7 +851,8 @@ static int lm75_detect(struct i2c_client *new_client,
 			return -ENODEV;
 	}
 
-	strlcpy(info->type, is_lm75a ? "lm75a" : "lm75", I2C_NAME_SIZE);
+	strlcpy(info->type, is_lm75a ? 
+		"lm75a" : (is_lm75b ? "lm75b" : "lm75"), I2C_NAME_SIZE);
 
 	return 0;
 }
-- 
2.21.0