i2c: Fix probing of FSC hardware monitoring chips

Some FSC hardware monitoring chips (Syleus at least) doesn't like
quick writes we typically use to probe for I2C chips. Use a regular
byte read instead for the address they live at (0x73). These are the
only known chips living at this address on PC systems.

For clarity, this fix should not be needed for kernels 2.6.30 and
later, as we started instantiating the hwmon devices explicitly based
on DMI data. Still, this fix is valuable in the following two cases:
* Support for recent FSC chips on older kernels. The DMI-based device
  instantiation is more difficult to backport than the device support
  itself.
* Case where the DMI-based device instantiation fails, whatever the
  reason. We fall back to probing in that case, so it should work.

This fixes kernel bug #15634:
https://bugzilla.kernel.org/show_bug.cgi?id=15634Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Cc: stable@kernel.org

drivers/i2c/i2c-core.c

@@ -1264,12 +1264,23 @@ static int i2c_detect_address(struct i2c_client *temp_client,
 		return 0;
 
 	/* Make sure there is something at this address */
-	if (i2c_smbus_xfer(adapter, addr, 0, 0, 0, I2C_SMBUS_QUICK, NULL) < 0)
+	if (addr == 0x73 && (adapter->class & I2C_CLASS_HWMON)) {
+		/* Special probe for FSC hwmon chips */
+		union i2c_smbus_data dummy;
+
+		if (i2c_smbus_xfer(adapter, addr, 0, I2C_SMBUS_READ, 0,
+				   I2C_SMBUS_BYTE_DATA, &dummy) < 0)
+			return 0;
+	} else {
+		if (i2c_smbus_xfer(adapter, addr, 0, I2C_SMBUS_WRITE, 0,
+				   I2C_SMBUS_QUICK, NULL) < 0)
 			return 0;
 
 		/* Prevent 24RF08 corruption */
 		if ((addr & ~0x0f) == 0x50)
-		i2c_smbus_xfer(adapter, addr, 0, 0, 0, I2C_SMBUS_QUICK, NULL);
+			i2c_smbus_xfer(adapter, addr, 0, I2C_SMBUS_WRITE, 0,
+				       I2C_SMBUS_QUICK, NULL);
+	}
 
 	/* Finally call the custom detection function */
 	memset(&info, 0, sizeof(struct i2c_board_info));