commit 942c1a927bf296fd64fd49f04c5a8f66bb14446b
author Per Dalén <per.dalen@appeartv.com> Thu May 26 09:08:53 2011 -0400
committer Guenter Roeck <guenter.roeck@ericsson.com> Sat Jun 04 10:34:28 2011 -0700
tree 58020f9137fd23755a918eca1ad0621109123a80
parent bb9973e4e73f43bd86698483d0c3f7a362ff94ce

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>

drivers/hwmon/max6642.c

diff --git a/drivers/hwmon/max6642.c b/drivers/hwmon/max6642.c
index 0f30e1b..e855d3b 100644
--- a/drivers/hwmon/max6642.c
+++ b/drivers/hwmon/max6642.c
@@ -136,15 +136,29 @@
 	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);