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Commit 7985e7c1 authored by Lars-Peter Clausen's avatar Lars-Peter Clausen Committed by Jonathan Cameron
Browse files

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: default avatarLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: default avatarJonathan Cameron <jic23@kernel.org>
parent ca7d1b32

drivers/iio/industrialio-core.c

+6 −0
Original line number Original line Diff line number Diff line
@@ -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 *indio_dev = dev_to_iio_dev(dev);

	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);

	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);

	unsigned long long tmp;

	int val, val2;

	int val, val2;

	bool scale_db = false;

	bool scale_db = false;

	int ret = indio_dev->info->read_raw(indio_dev, this_attr->c,

	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);

			return sprintf(buf, "-%d.%09u\n", val, -val2);

		else

		else

			return sprintf(buf, "%d.%09u\n", val, val2);

			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:

	default:

		return 0;

		return 0;

	}

	}

include/linux/iio/types.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -57,5 +57,6 @@ enum iio_modifier { 
#define IIO_VAL_INT_PLUS_MICRO 2

#define IIO_VAL_INT_PLUS_MICRO 2

#define IIO_VAL_INT_PLUS_NANO 3

#define IIO_VAL_INT_PLUS_NANO 3

#define IIO_VAL_INT_PLUS_MICRO_DB 4

#define IIO_VAL_INT_PLUS_MICRO_DB 4

#define IIO_VAL_FRACTIONAL 10





#endif /* _IIO_TYPES_H_ */
 
#endif /* _IIO_TYPES_H_ */