This series is just a request for comments right now and at this point it is
barley tested.
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
precession.
Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
---
drivers/iio/industrialio-core.c | 9 +++++++++
include/linux/iio/types.h | 1 +
2 files changed, 10 insertions(+)
diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 2ec266e..69e60c5 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -365,6 +365,7 @@ 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,
@@ -390,6 +391,14 @@ 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);
+
+ /* Or maybe we could do something like this:
+ return sprintf(buf, "%d/%d\n", val, val2); */
default:
return 0;
}
diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
index 44e3977..8ef5fde 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 5
#endif /* _IIO_TYPES_H_ */
--
1.7.10.4
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