iio: core: add function to retrieve active_scan_mask index

Add a function to retrieve the index of the active scan mask inside the
available scan masks array.

As in iio_scan_mask_match and iio_sanity_check_avail_scan_masks,
this function does not handle multi-long masks correctly.
It only checks the first long to be zero, and will use such mask
as a terminator even if there was bits set after the first long.

This should be fine since the available_scan_mask has already been
sanity tested using iio_sanity_check_avail_scan_masks.

See iio_scan_mask_match and iio_sanity_check_avail_scan_masks for
more details
Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20240731-ad7380-add-single-ended-chips-v2-2-cd63bf05744c@baylibre.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-core.c

@@ -1965,6 +1965,49 @@ static void iio_sanity_check_avail_scan_masks(struct iio_dev *indio_dev)
 	}
 }
 
+/**
+ * iio_active_scan_mask_index - Get index of the active scan mask inside the
+ * available scan masks array
+ * @indio_dev: the IIO device containing the active and available scan masks
+ *
+ * Returns: the index or -EINVAL if  active_scan_mask is not set
+ */
+int iio_active_scan_mask_index(struct iio_dev *indio_dev)
+
+{
+	const unsigned long *av_masks;
+	unsigned int masklength = iio_get_masklength(indio_dev);
+	int i = 0;
+
+	if (!indio_dev->active_scan_mask)
+		return -EINVAL;
+
+	/*
+	 * As in iio_scan_mask_match and iio_sanity_check_avail_scan_masks,
+	 * the condition here do not handle multi-long masks correctly.
+	 * It only checks the first long to be zero, and will use such mask
+	 * as a terminator even if there was bits set after the first long.
+	 *
+	 * This should be fine since the available_scan_mask has already been
+	 * sanity tested using iio_sanity_check_avail_scan_masks.
+	 *
+	 * See iio_scan_mask_match and iio_sanity_check_avail_scan_masks for
+	 * more details
+	 */
+	av_masks = indio_dev->available_scan_masks;
+	while (*av_masks) {
+		if (indio_dev->active_scan_mask == av_masks)
+			return i;
+		av_masks += BITS_TO_LONGS(masklength);
+		i++;
+	}
+
+	dev_warn(indio_dev->dev.parent,
+		 "active scan mask is not part of the avaialable scan masks\n");
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(iio_active_scan_mask_index);
+
 int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
 {
 	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);

include/linux/iio/iio.h

@@ -864,6 +864,8 @@ static inline unsigned int iio_get_masklength(const struct iio_dev *indio_dev)
 	return ACCESS_PRIVATE(indio_dev, masklength);
 }
 
+int iio_active_scan_mask_index(struct iio_dev *indio_dev);
+
 /**
  * iio_for_each_active_channel - Iterated over active channels
  * @indio_dev: the IIO device