From 7985e7c1003bc5cdfa20755f8cfdada946ed8e18 Mon Sep 17 00:00:00 2001
From: Lars-Peter Clausen <lars@metafoo.de>
Date: Fri, 14 Sep 2012 16:21:00 +0100
Subject: [PATCH] iio: Introduce a new fractional value type

Currently IIO uses a decimal fixed point representations for real type numbers.
This patch introduces a new representation for rational type numbers. The number
will be expressed by specifying a numerator and denominator. For converting a
raw value to a processed value multiply it by the numerator and divide it by the
denominator.

The reasoning for introducing this new type is that for a lot of devices the
scale can be represented easily by a fractional number, but it is not possible
to represent it as fixed point number without rounding.  E.g. for a simple DAC
the scale is often the reference voltage divided by the number of possible
values (Usually 2**n_bits - 1). Each driver currently implements the conversion
of this fraction to a fixed point number on its own.

Also when it comes to the in-kernel interface this allows to directly use the
fractional factors to convert a raw value to a processed value. This should on
one hand require less instructions and on the other hand increase the
precision.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
---
 drivers/iio/industrialio-core.c | 6 ++++++
 include/linux/iio/types.h       | 1 +
 2 files changed, 7 insertions(+)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 0499330d6e98..6eb24dbc081e 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -366,6 +366,7 @@ static ssize_t iio_read_channel_info(struct device *dev,
 {
 	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
+	unsigned long long tmp;
 	int val, val2;
 	bool scale_db = false;
 	int ret = indio_dev->info->read_raw(indio_dev, this_attr->c,
@@ -391,6 +392,11 @@ static ssize_t iio_read_channel_info(struct device *dev,
 			return sprintf(buf, "-%d.%09u\n", val, -val2);
 		else
 			return sprintf(buf, "%d.%09u\n", val, val2);
+	case IIO_VAL_FRACTIONAL:
+		tmp = div_s64((s64)val * 1000000000LL, val2);
+		val2 = do_div(tmp, 1000000000LL);
+		val = tmp;
+		return sprintf(buf, "%d.%09u\n", val, val2);
 	default:
 		return 0;
 	}
diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
index 44e397705d7f..5c647ecfd5ba 100644
--- a/include/linux/iio/types.h
+++ b/include/linux/iio/types.h
@@ -57,5 +57,6 @@ enum iio_modifier {
 #define IIO_VAL_INT_PLUS_MICRO 2
 #define IIO_VAL_INT_PLUS_NANO 3
 #define IIO_VAL_INT_PLUS_MICRO_DB 4
+#define IIO_VAL_FRACTIONAL 10
 
 #endif /* _IIO_TYPES_H_ */
-- 
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