hwmon: (dell-smm) Detect fan with index=2

Some Dell machines (e.g. Dell Precision M3800) have two fans, first with
index=0 and second with index=2. So export also attributes for third fan
device with index=2.
Reported-by: Tolga Cakir <cevelnet@gmail.com>
Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Tolga Cakir <cevelnet@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/dell-smm-hwmon.c

@@ -81,6 +81,7 @@ static bool disallow_fan_type_call;
 #define I8K_HWMON_HAVE_TEMP4	(1 << 3)
 #define I8K_HWMON_HAVE_FAN1	(1 << 4)
 #define I8K_HWMON_HAVE_FAN2	(1 << 5)
+#define I8K_HWMON_HAVE_FAN3	(1 << 6)
 
 MODULE_AUTHOR("Massimo Dal Zotto (dz@debian.org)");
 MODULE_AUTHOR("Pali Rohár <pali.rohar@gmail.com>");
@@ -252,7 +253,7 @@ static int _i8k_get_fan_type(int fan)
 static int i8k_get_fan_type(int fan)
 {
 	/* I8K_SMM_GET_FAN_TYPE SMM call is expensive, so cache values */
-	static int types[2] = { INT_MIN, INT_MIN };
+	static int types[3] = { INT_MIN, INT_MIN, INT_MIN };
 
 	if (types[fan] == INT_MIN)
 		types[fan] = _i8k_get_fan_type(fan);
@@ -719,6 +720,12 @@ static SENSOR_DEVICE_ATTR(fan2_label, S_IRUGO, i8k_hwmon_show_fan_label, NULL,
 			  1);
 static SENSOR_DEVICE_ATTR(pwm2, S_IRUGO | S_IWUSR, i8k_hwmon_show_pwm,
 			  i8k_hwmon_set_pwm, 1);
+static SENSOR_DEVICE_ATTR(fan3_input, S_IRUGO, i8k_hwmon_show_fan, NULL,
+			  2);
+static SENSOR_DEVICE_ATTR(fan3_label, S_IRUGO, i8k_hwmon_show_fan_label, NULL,
+			  2);
+static SENSOR_DEVICE_ATTR(pwm3, S_IRUGO | S_IWUSR, i8k_hwmon_show_pwm,
+			  i8k_hwmon_set_pwm, 2);
 
 static struct attribute *i8k_attrs[] = {
 	&sensor_dev_attr_temp1_input.dev_attr.attr,	/* 0 */
@@ -735,6 +742,9 @@ static struct attribute *i8k_attrs[] = {
 	&sensor_dev_attr_fan2_input.dev_attr.attr,	/* 11 */
 	&sensor_dev_attr_fan2_label.dev_attr.attr,	/* 12 */
 	&sensor_dev_attr_pwm2.dev_attr.attr,		/* 13 */
+	&sensor_dev_attr_fan3_input.dev_attr.attr,	/* 14 */
+	&sensor_dev_attr_fan3_label.dev_attr.attr,	/* 15 */
+	&sensor_dev_attr_pwm3.dev_attr.attr,		/* 16 */
 	NULL
 };
 
@@ -742,7 +752,7 @@ static umode_t i8k_is_visible(struct kobject *kobj, struct attribute *attr,
 			      int index)
 {
 	if (disallow_fan_type_call &&
-	    (index == 9 || index == 12))
+	    (index == 9 || index == 12 || index == 15))
 		return 0;
 	if (index >= 0 && index <= 1 &&
 	    !(i8k_hwmon_flags & I8K_HWMON_HAVE_TEMP1))
@@ -762,6 +772,9 @@ static umode_t i8k_is_visible(struct kobject *kobj, struct attribute *attr,
 	if (index >= 11 && index <= 13 &&
 	    !(i8k_hwmon_flags & I8K_HWMON_HAVE_FAN2))
 		return 0;
+	if (index >= 14 && index <= 16 &&
+	    !(i8k_hwmon_flags & I8K_HWMON_HAVE_FAN3))
+		return 0;
 
 	return attr->mode;
 }
@@ -807,6 +820,13 @@ static int __init i8k_init_hwmon(void)
 	if (err >= 0)
 		i8k_hwmon_flags |= I8K_HWMON_HAVE_FAN2;
 
+	/* Third fan attributes, if fan status or type is OK */
+	err = i8k_get_fan_status(2);
+	if (err < 0)
+		err = i8k_get_fan_type(2);
+	if (err >= 0)
+		i8k_hwmon_flags |= I8K_HWMON_HAVE_FAN3;
+
 	i8k_hwmon_dev = hwmon_device_register_with_groups(NULL, "dell_smm",
 							  NULL, i8k_groups);
 	if (IS_ERR(i8k_hwmon_dev)) {