include/linux/units.h: add helpers for kelvin to/from Celsius conversion

Patch series "add header file for kelvin to/from Celsius conversion
helpers", v4.

There are several helper macros to convert kelvin to/from Celsius in
<linux/thermal.h> for thermal drivers.  These are useful for any other
drivers or subsystems, but it's odd to include <linux/thermal.h> just
for the helpers.

This adds a new <linux/units.h> that provides the equivalent inline
functions for any drivers or subsystems, and switches all the users of
conversion helpers in <linux/thermal.h> to use <linux/units.h> helpers.

This patch (of 12):

There are several helper macros to convert kelvin to/from Celsius in
<linux/thermal.h> for thermal drivers.  These are useful for any other
drivers or subsystems, but it's odd to include <linux/thermal.h> just
for the helpers.

This adds a new <linux/units.h> that provides the equivalent inline
functions for any drivers or subsystems.  It is intended to replace the
helpers in <linux/thermal.h>.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Akinobu Mita <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Cc: Sujith Thomas <[email protected]>
Cc: Darren Hart <[email protected]>
Cc: Zhang Rui <[email protected]>
Cc: Daniel Lezcano <[email protected]>
Cc: Amit Kucheria <[email protected]>
Cc: Jean Delvare <[email protected]>
Cc: Guenter Roeck <[email protected]>
Cc: Keith Busch <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Sagi Grimberg <[email protected]>
Cc: Kalle Valo <[email protected]>
Cc: Stanislaw Gruszka <[email protected]>
Cc: Johannes Berg <[email protected]>
Cc: Emmanuel Grumbach <[email protected]>
Cc: Luca Coelho <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Hartmut Knaack <[email protected]>
Cc: Lars-Peter Clausen <[email protected]>
Cc: Peter Meerwald-Stadler <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/units.h

@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_UNITS_H
+#define _LINUX_UNITS_H
+
+#include <linux/kernel.h>
+
+#define ABSOLUTE_ZERO_MILLICELSIUS -273150
+
+static inline long milli_kelvin_to_millicelsius(long t)
+{
+	return t + ABSOLUTE_ZERO_MILLICELSIUS;
+}
+
+static inline long millicelsius_to_milli_kelvin(long t)
+{
+	return t - ABSOLUTE_ZERO_MILLICELSIUS;
+}
+
+#define MILLIDEGREE_PER_DEGREE 1000
+#define MILLIDEGREE_PER_DECIDEGREE 100
+
+static inline long kelvin_to_millicelsius(long t)
+{
+	return milli_kelvin_to_millicelsius(t * MILLIDEGREE_PER_DEGREE);
+}
+
+static inline long millicelsius_to_kelvin(long t)
+{
+	t = millicelsius_to_milli_kelvin(t);
+
+	return DIV_ROUND_CLOSEST(t, MILLIDEGREE_PER_DEGREE);
+}
+
+static inline long deci_kelvin_to_celsius(long t)
+{
+	t = milli_kelvin_to_millicelsius(t * MILLIDEGREE_PER_DECIDEGREE);
+
+	return DIV_ROUND_CLOSEST(t, MILLIDEGREE_PER_DEGREE);
+}
+
+static inline long celsius_to_deci_kelvin(long t)
+{
+	t = millicelsius_to_milli_kelvin(t * MILLIDEGREE_PER_DEGREE);
+
+	return DIV_ROUND_CLOSEST(t, MILLIDEGREE_PER_DECIDEGREE);
+}
+
+/**
+ * deci_kelvin_to_millicelsius_with_offset - convert Kelvin to Celsius
+ * @t: temperature value in decidegrees Kelvin
+ * @offset: difference between Kelvin and Celsius in millidegrees
+ *
+ * Return: temperature value in millidegrees Celsius
+ */
+static inline long deci_kelvin_to_millicelsius_with_offset(long t, long offset)
+{
+	return t * MILLIDEGREE_PER_DECIDEGREE - offset;
+}
+
+static inline long deci_kelvin_to_millicelsius(long t)
+{
+	return milli_kelvin_to_millicelsius(t * MILLIDEGREE_PER_DECIDEGREE);
+}
+
+static inline long millicelsius_to_deci_kelvin(long t)
+{
+	t = millicelsius_to_milli_kelvin(t);
+
+	return DIV_ROUND_CLOSEST(t, MILLIDEGREE_PER_DECIDEGREE);
+}
+
+static inline long kelvin_to_celsius(long t)
+{
+	return t + DIV_ROUND_CLOSEST(ABSOLUTE_ZERO_MILLICELSIUS,
+				     MILLIDEGREE_PER_DEGREE);
+}
+
+static inline long celsius_to_kelvin(long t)
+{
+	return t - DIV_ROUND_CLOSEST(ABSOLUTE_ZERO_MILLICELSIUS,
+				     MILLIDEGREE_PER_DEGREE);
+}
+
+#endif /* _LINUX_UNITS_H */