iio: afe: rescale: expose scale processing function

In preparation for the addition of kunit tests, expose the logic
responsible for combining channel scales.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220213025739.2561834-2-liambeguin@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

include/linux/iio/afe/rescale.h

@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2018 Axentia Technologies AB
+ */
+
+#ifndef __IIO_RESCALE_H__
+#define __IIO_RESCALE_H__
+
+#include <linux/types.h>
+#include <linux/iio/iio.h>
+
+struct device;
+struct rescale;
+
+struct rescale_cfg {
+	enum iio_chan_type type;
+	int (*props)(struct device *dev, struct rescale *rescale);
+};
+
+struct rescale {
+	const struct rescale_cfg *cfg;
+	struct iio_channel *source;
+	struct iio_chan_spec chan;
+	struct iio_chan_spec_ext_info *ext_info;
+	bool chan_processed;
+	s32 numerator;
+	s32 denominator;
+};
+
+int rescale_process_scale(struct rescale *rescale, int scale_type,
+			  int *val, int *val2);
+#endif /* __IIO_RESCALE_H__ */