[v3,01/12] add helpers for kelvin to/from Celsius conversion

Commit Message

Akinobu Mita Dec. 11, 2019, 2:38 p.m. UTC

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>.

Cc: Sujith Thomas <[e-mail]>
Cc: Darren Hart <[e-mail]>
Cc: Andy Shevchenko <[e-mail]>
Cc: Zhang Rui <[e-mail]>
Cc: Daniel Lezcano <[e-mail]>
Cc: Amit Kucheria <[e-mail]>
Cc: Jean Delvare <[e-mail]>
Cc: Guenter Roeck <[e-mail]>
Cc: Keith Busch <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Sagi Grimberg <[e-mail]>
Cc: Kalle Valo <[e-mail]>
Cc: Stanislaw Gruszka <[e-mail]>
Cc: Johannes Berg <[e-mail]>
Cc: Emmanuel Grumbach <[e-mail]>
Cc: Luca Coelho <[e-mail]>
Cc: Intel Linux Wireless <[e-mail]>
Cc: Jonathan Cameron <[e-mail]>
Cc: Hartmut Knaack <[e-mail]>
Cc: Lars-Peter Clausen <[e-mail]>
Cc: Peter Meerwald-Stadler <[e-mail]>
Signed-off-by: Akinobu Mita <[e-mail]>
---
* v3
- rename new header name from <linux/temperature.h> to <linux/units.h>
- add milli_kelvin_to_millicelsius() and millicelsius_to_milli_kelvin() and
  use them for implementing other helpers
- add MILLIDEGREE_PER_DEGREE and MILLIDEGREE_PER_DECIDEGREE and replace
  the hardcoded constants
- add kelvin_to_celsius() and celsius_to_kelvin() in <linux/units.h>

 include/linux/units.h | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 include/linux/units.h

Patch

diff --git a/include/linux/units.h b/include/linux/units.h
new file mode 100644
index 0000000..aaf7163
--- /dev/null
+++ b/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 */