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

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
...@@ -366,6 +366,7 @@ static ssize_t iio_read_channel_info(struct device *dev, ...@@ -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, ...@@ -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;
} }
......
...@@ -57,5 +57,6 @@ enum iio_modifier { ...@@ -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_ */
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