iio: Introduce iio_validate_scan_mask_onehot

Add a helper function for validating a scan mask for devices where exactly one
channel must be selected during sampling. This is a common case among devices
which have scan mask restrictions so it makes sense to provide this function in
the core.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-buffer.c

@@ -570,6 +570,22 @@ int iio_sw_buffer_preenable(struct iio_dev *indio_dev)
 }
 EXPORT_SYMBOL(iio_sw_buffer_preenable);
 
+/**
+ * iio_validate_scan_mask_onehot() - Validates that exactly one channel is selected
+ * @indio_dev: the iio device
+ * @mask: scan mask to be checked
+ *
+ * Return true if exactly one bit is set in the scan mask, false otherwise. It
+ * can be used for devices where only one channel can be active for sampling at
+ * a time.
+ */
+bool iio_validate_scan_mask_onehot(struct iio_dev *indio_dev,
+	const unsigned long *mask)
+{
+	return bitmap_weight(mask, indio_dev->masklength) == 1;
+}
+EXPORT_SYMBOL_GPL(iio_validate_scan_mask_onehot);
+
 static bool iio_validate_scan_mask(struct iio_dev *indio_dev,
 	const unsigned long *mask)
 {

include/linux/iio/buffer.h

@@ -177,6 +177,9 @@ ssize_t iio_buffer_show_enable(struct device *dev,
 
 int iio_sw_buffer_preenable(struct iio_dev *indio_dev);
 
+bool iio_validate_scan_mask_onehot(struct iio_dev *indio_dev,
+	const unsigned long *mask);
+
 #else /* CONFIG_IIO_BUFFER */
 
 static inline int iio_buffer_register(struct iio_dev *indio_dev,