Merge tag 'hwmon-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging

Pull hwmon fix from Guenter Roeck:
 "Improve chip detection in ADM1021 driver to avoid misdetections

  This is not a critical patch, but one we'll want to have applied to
  -stable, since the misdetection especially of LM84 has been causing
  trouble for quite some time."

* tag 'hwmon-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging:
  hwmon: (adm1021) Strengthen chip detection for ADM1021, LM84 and MAX1617

drivers/hwmon/adm1021.c

@@ -331,26 +331,68 @@ static int adm1021_detect(struct i2c_client *client,
 	man_id = i2c_smbus_read_byte_data(client, ADM1021_REG_MAN_ID);
 	dev_id = i2c_smbus_read_byte_data(client, ADM1021_REG_DEV_ID);
 
+	if (man_id < 0 || dev_id < 0)
+		return -ENODEV;
+
 	if (man_id == 0x4d && dev_id == 0x01)
 		type_name = "max1617a";
 	else if (man_id == 0x41) {
 		if ((dev_id & 0xF0) == 0x30)
 			type_name = "adm1023";
-		else
+		else if ((dev_id & 0xF0) == 0x00)
 			type_name = "adm1021";
+		else
+			return -ENODEV;
 	} else if (man_id == 0x49)
 		type_name = "thmc10";
 	else if (man_id == 0x23)
 		type_name = "gl523sm";
 	else if (man_id == 0x54)
 		type_name = "mc1066";
-	/* LM84 Mfr ID in a different place, and it has more unused bits */
-	else if (conv_rate == 0x00
-		 && (config & 0x7F) == 0x00
-		 && (status & 0xAB) == 0x00)
-		type_name = "lm84";
-	else
-		type_name = "max1617";
+	else {
+		int lte, rte, lhi, rhi, llo, rlo;
+
+		/* extra checks for LM84 and MAX1617 to avoid misdetections */
+
+		llo = i2c_smbus_read_byte_data(client, ADM1021_REG_THYST_R(0));
+		rlo = i2c_smbus_read_byte_data(client, ADM1021_REG_THYST_R(1));
+
+		/* fail if any of the additional register reads failed */
+		if (llo < 0 || rlo < 0)
+			return -ENODEV;
+
+		lte = i2c_smbus_read_byte_data(client, ADM1021_REG_TEMP(0));
+		rte = i2c_smbus_read_byte_data(client, ADM1021_REG_TEMP(1));
+		lhi = i2c_smbus_read_byte_data(client, ADM1021_REG_TOS_R(0));
+		rhi = i2c_smbus_read_byte_data(client, ADM1021_REG_TOS_R(1));
+
+		/*
+		 * Fail for negative temperatures and negative high limits.
+		 * This check also catches read errors on the tested registers.
+		 */
+		if ((s8)lte < 0 || (s8)rte < 0 || (s8)lhi < 0 || (s8)rhi < 0)
+			return -ENODEV;
+
+		/* fail if all registers hold the same value */
+		if (lte == rte && lte == lhi && lte == rhi && lte == llo
+		    && lte == rlo)
+			return -ENODEV;
+
+		/*
+		 * LM84 Mfr ID is in a different place,
+		 * and it has more unused bits.
+		 */
+		if (conv_rate == 0x00
+		    && (config & 0x7F) == 0x00
+		    && (status & 0xAB) == 0x00) {
+			type_name = "lm84";
+		} else {
+			/* fail if low limits are larger than high limits */
+			if ((s8)llo > lhi || (s8)rlo > rhi)
+				return -ENODEV;
+			type_name = "max1617";
+		}
+	}
 
 	pr_debug("Detected chip %s at adapter %d, address 0x%02x.\n",
 		 type_name, i2c_adapter_id(adapter), client->addr);