iio: trigger: Add simple trigger_validation helper

Some triggers can only be attached to the IIO device that corresponds to
the same physical device. Implement generic helper which can be used as
a validate_trigger callback for such devices.
Suggested-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/51cd3e3e74a6addf8d333f4a109fb9c5a11086ee.1683541225.git.mazziesaccount@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-trigger.c

@@ -322,7 +322,7 @@ int iio_trigger_attach_poll_func(struct iio_trigger *trig,
 	 * this is the case if the IIO device and the trigger device share the
 	 * same parent device.
 	 */
-	if (pf->indio_dev->dev.parent == trig->dev.parent)
+	if (iio_validate_own_trigger(pf->indio_dev, trig))
 		trig->attached_own_device = true;
 
 	return ret;
@@ -728,6 +728,26 @@ bool iio_trigger_using_own(struct iio_dev *indio_dev)
 }
 EXPORT_SYMBOL(iio_trigger_using_own);
 
+/**
+ * iio_validate_own_trigger - Check if a trigger and IIO device belong to
+ *  the same device
+ * @idev: the IIO device to check
+ * @trig: the IIO trigger to check
+ *
+ * This function can be used as the validate_trigger callback for triggers that
+ * can only be attached to their own device.
+ *
+ * Return: 0 if both the trigger and the IIO device belong to the same
+ * device, -EINVAL otherwise.
+ */
+int iio_validate_own_trigger(struct iio_dev *idev, struct iio_trigger *trig)
+{
+	if (idev->dev.parent != trig->dev.parent)
+		return -EINVAL;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iio_validate_own_trigger);
+
 /**
  * iio_trigger_validate_own_device - Check if a trigger and IIO device belong to
  *  the same device

include/linux/iio/trigger.h

@@ -171,6 +171,7 @@ void iio_trigger_free(struct iio_trigger *trig);
  */
 bool iio_trigger_using_own(struct iio_dev *indio_dev);
 
+int iio_validate_own_trigger(struct iio_dev *idev, struct iio_trigger *trig);
 int iio_trigger_validate_own_device(struct iio_trigger *trig,
 				     struct iio_dev *indio_dev);