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>
diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 0499330..6eb24db 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -366,6 +366,7 @@
{
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 @@
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;
}