hwmon: (max6642): Better chip detection schema

Improve detection of MAX6642 by reading non existing registers (0x04, 0x06
and 0xff). Reading those registers returns the previously read value.

Signed-off-by: Per Dalen <per.dalen@appeartv.com>
[guenter.roeck@ericsson.com: added second set of register reads]
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/drivers/hwmon/max6642.c b/drivers/hwmon/max6642.c
index 0f30e1bb366f..e855d3b0bd1f 100644
--- a/drivers/hwmon/max6642.c
+++ b/drivers/hwmon/max6642.c
@@ -136,15 +136,29 @@ static int max6642_detect(struct i2c_client *client,
         if (man_id != 0x4D)
                 return -ENODEV;
 
+        /* sanity check */
+        if (i2c_smbus_read_byte_data(client, 0x04) != 0x4D
+            || i2c_smbus_read_byte_data(client, 0x06) != 0x4D
+            || i2c_smbus_read_byte_data(client, 0xff) != 0x4D)
+                return -ENODEV;
+
         /*
          * We read the config and status register, the 4 lower bits in the
          * config register should be zero and bit 5, 3, 1 and 0 should be
          * zero in the status register.
          */
         reg_config = i2c_smbus_read_byte_data(client, MAX6642_REG_R_CONFIG);
+        if ((reg_config & 0x0f) != 0x00)
+                return -ENODEV;
+
+        /* in between, another round of sanity checks */
+        if (i2c_smbus_read_byte_data(client, 0x04) != reg_config
+            || i2c_smbus_read_byte_data(client, 0x06) != reg_config
+            || i2c_smbus_read_byte_data(client, 0xff) != reg_config)
+                return -ENODEV;
+
         reg_status = i2c_smbus_read_byte_data(client, MAX6642_REG_R_STATUS);
-        if (((reg_config & 0x0f) != 0x00) ||
-            ((reg_status & 0x2b) != 0x00))
+        if ((reg_status & 0x2b) != 0x00)
                 return -ENODEV;
 
         strlcpy(info->type, "max6642", I2C_NAME_SIZE);