hwmon: (w83627ehf) Disable setting DC mode for pwm2, pwm3 on NCT6776F

NCT6776F only supports pwm mode for pwm2 and pwm3. Return error if an attempt
is made to set those pwm channels to DC mode.
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Acked-by: NJean Delvare <khali@linux-fr.org>
Cc: stable@vger.kernel.org # 3.0+
Signed-off-by: NGuenter Roeck <guenter.roeck@ericsson.com>

drivers/hwmon/w83627ehf.c

@@ -1319,6 +1319,7 @@ store_pwm_mode(struct device *dev, struct device_attribute *attr,
 {
 	struct w83627ehf_data *data = dev_get_drvdata(dev);
 	struct sensor_device_attribute *sensor_attr = to_sensor_dev_attr(attr);
+	struct w83627ehf_sio_data *sio_data = dev->platform_data;
 	int nr = sensor_attr->index;
 	unsigned long val;
 	int err;
@@ -1330,6 +1331,11 @@ store_pwm_mode(struct device *dev, struct device_attribute *attr,
 
 	if (val > 1)
 		return -EINVAL;
+
+	/* On NCT67766F, DC mode is only supported for pwm1 */
+	if (sio_data->kind == nct6776 && nr && val != 1)
+		return -EINVAL;
+
 	mutex_lock(&data->update_lock);
 	reg = w83627ehf_read_value(data, W83627EHF_REG_PWM_ENABLE[nr]);
 	data->pwm_mode[nr] = val;