3 files changed, 47 insertions, 16 deletions

diff --git a/Documentation/hwmon/lm75 b/Documentation/hwmon/lm75
index 8e6356fe05d7..a1790401fdde 100644
--- a/Documentation/hwmon/lm75
+++ b/Documentation/hwmon/lm75
@@ -7,6 +7,11 @@ Supported chips:
     Addresses scanned: I2C 0x48 - 0x4f
     Datasheet: Publicly available at the National Semiconductor website
                http://www.national.com/
+  * National Semiconductor LM75A
+    Prefix: 'lm75a'
+    Addresses scanned: I2C 0x48 - 0x4f
+    Datasheet: Publicly available at the National Semiconductor website
+               http://www.national.com/
   * Dallas Semiconductor DS75
     Prefix: 'lm75'
     Addresses scanned: I2C 0x48 - 0x4f
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 47621abb9a05..19d72bcf966a 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -521,7 +521,7 @@ config SENSORS_LM75
                 - Dallas Semiconductor DS75 and DS1775
                 - Maxim MAX6625 and MAX6626
                 - Microchip MCP980x
-                - National Semiconductor LM75
+                - National Semiconductor LM75, LM75A
                 - NXP's LM75A
                 - ST Microelectronics STDS75
                 - TelCom (now Microchip) TCN75
diff --git a/drivers/hwmon/lm75.c b/drivers/hwmon/lm75.c
index f36eb80d227f..638dd0586e3f 100644
--- a/drivers/hwmon/lm75.c
+++ b/drivers/hwmon/lm75.c
@@ -232,6 +232,8 @@ static const struct i2c_device_id lm75_ids[] = {
 };
 MODULE_DEVICE_TABLE(i2c, lm75_ids);
 
+#define LM75A_ID 0xA1
+
 /* Return 0 if detection is successful, -ENODEV otherwise */
 static int lm75_detect(struct i2c_client *new_client,
                        struct i2c_board_info *info)
@@ -239,6 +241,7 @@ static int lm75_detect(struct i2c_client *new_client,
         struct i2c_adapter *adapter = new_client->adapter;
         int i;
         int cur, conf, hyst, os;
+        bool is_lm75a = 0;
 
         if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA |
                                      I2C_FUNC_SMBUS_WORD_DATA))
@@ -250,23 +253,43 @@ static int lm75_detect(struct i2c_client *new_client,
            addresses 0x04-0x07 returning the last read value.
            The cycling+unused addresses combination is not tested,
            since it would significantly slow the detection down and would
-           hardly add any value. */
+           hardly add any value.
+
+           The National Semiconductor LM75A is different than earlier
+           LM75s.  It has an ID byte of 0xaX (where X is the chip
+           revision, with 1 being the only revision in existence) in
+           register 7, and unused registers return 0xff rather than the
+           last read value. */
 
-        /* Unused addresses */
         cur = i2c_smbus_read_word_data(new_client, 0);
         conf = i2c_smbus_read_byte_data(new_client, 1);
-        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)
-                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)
-                return -ENODEV;
+
+        /* First check for LM75A */
+        if (i2c_smbus_read_byte_data(new_client, 7) == LM75A_ID) {
+                /* LM75A returns 0xff on unused registers so
+                   just to be sure we check for that too. */
+                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)
+                        return -ENODEV;
+                is_lm75a = 1;
+                hyst = i2c_smbus_read_word_data(new_client, 2);
+                os = i2c_smbus_read_word_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)
+                        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)
+                        return -ENODEV;
+        }
 
         /* Unused bits */
         if (conf & 0xe0)
@@ -278,9 +301,12 @@ static int lm75_detect(struct i2c_client *new_client,
                  || i2c_smbus_read_word_data(new_client, i + 2) != hyst
                  || i2c_smbus_read_word_data(new_client, i + 3) != os)
                         return -ENODEV;
+                if (is_lm75a && i2c_smbus_read_byte_data(new_client, i + 7)
+                                != LM75A_ID)
+                        return -ENODEV;
         }
 
-        strlcpy(info->type, "lm75", I2C_NAME_SIZE);
+        strlcpy(info->type, is_lm75a ? "lm75a" : "lm75", I2C_NAME_SIZE);
 
         return 0;
 }