hwmon: (i5500_temp) Don't bind to disabled sensors

On many motherboards, for an unknown reason, the thermal sensor seems
to be disabled and will return a constant temperature value of 36.5
degrees Celsius. Don't bind to the device in that case, so that we
don't report this bogus value to userspace.
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Romain Dolbeau <romain@dolbeau.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/i5500_temp.c

@@ -121,6 +121,8 @@ static int i5500_temp_probe(struct pci_dev *pdev,
 {
 	int err;
 	struct device *hwmon_dev;
+	u32 tstimer;
+	s8 tsfsc;
 
 	err = pci_enable_device(pdev);
 	if (err) {
@@ -128,6 +130,13 @@ static int i5500_temp_probe(struct pci_dev *pdev,
 		return err;
 	}
 
+	pci_read_config_byte(pdev, REG_TSFSC, &tsfsc);
+	pci_read_config_dword(pdev, REG_TSTIMER, &tstimer);
+	if (tsfsc == 0x7F && tstimer == 0x07D30D40) {
+		dev_warn(&pdev->dev, "Sensor seems to be disabled\n");
+		return -ENODEV;
+	}
+
 	hwmon_dev = devm_hwmon_device_register_with_groups(&pdev->dev,
 							   "intel5500", NULL,
 							   i5500_temp_groups);