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authorLars-Peter Clausen <lars@metafoo.de>2015-08-05 15:38:14 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-09-21 10:02:16 -0700
commit3ae8f4061f5c01a7894ae118b53f22fd4ea82740 (patch)
tree3623e39f854c413b44afdfd2744857400f412bf4
parentde1cd705e3173dd268a505e69a7ece661017db86 (diff)
downloadlwn-3ae8f4061f5c01a7894ae118b53f22fd4ea82740.tar.gz
lwn-3ae8f4061f5c01a7894ae118b53f22fd4ea82740.zip
iio: Add inverse unit conversion macros
commit c689a923c867eac40ed3826c1d9328edea8b6bc7 upstream. Add inverse unit conversion macro to convert from standard IIO units to units that might be used by some devices. Those are useful in combination with scale factors that are specified as IIO_VAL_FRACTIONAL. Typically the denominator for those specifications will contain the maximum raw value the sensor will generate and the numerator the value it maps to in a specific unit. Sometimes datasheets specify those in different units than the standard IIO units (e.g. degree/s instead of rad/s) and so we need to do a unit conversion. From a mathematical point of view it does not make a difference whether we apply the unit conversion to the numerator or the inverse unit conversion to the denominator since (x / y) / z = x / (y * z). But as the denominator is typically a larger value and we are rounding both the numerator and denominator to integer values using the later method gives us a better precision (E.g. the relative error is smaller if we round 8000.3 to 8000 rather than rounding 8.3 to 8). This is where in inverse unit conversion macros will be used. Marked for stable as used by some upcoming fixes. Signed-off-by: Lars-Peter Clausen <lars@metafoo.de> Signed-off-by: Jonathan Cameron <jic23@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--include/linux/iio/iio.h17
1 files changed, 17 insertions, 0 deletions
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 75a8a20c8179..c2fb6f3ff44b 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -593,6 +593,15 @@ int iio_str_to_fixpoint(const char *str, int fract_mult, int *integer,
#define IIO_DEGREE_TO_RAD(deg) (((deg) * 314159ULL + 9000000ULL) / 18000000ULL)
/**
+ * IIO_RAD_TO_DEGREE() - Convert rad to degree
+ * @rad: A value in rad
+ *
+ * Returns the given value converted from rad to degree
+ */
+#define IIO_RAD_TO_DEGREE(rad) \
+ (((rad) * 18000000ULL + 314159ULL / 2) / 314159ULL)
+
+/**
* IIO_G_TO_M_S_2() - Convert g to meter / second**2
* @g: A value in g
*
@@ -600,4 +609,12 @@ int iio_str_to_fixpoint(const char *str, int fract_mult, int *integer,
*/
#define IIO_G_TO_M_S_2(g) ((g) * 980665ULL / 100000ULL)
+/**
+ * IIO_M_S_2_TO_G() - Convert meter / second**2 to g
+ * @ms2: A value in meter / second**2
+ *
+ * Returns the given value converted from meter / second**2 to g
+ */
+#define IIO_M_S_2_TO_G(ms2) (((ms2) * 100000ULL + 980665ULL / 2) / 980665ULL)
+
#endif /* _INDUSTRIAL_IO_H_ */