v4.19.13 snapshot.
diff --git a/include/linux/average.h b/include/linux/average.h
new file mode 100644
index 0000000..a1a8f09
--- /dev/null
+++ b/include/linux/average.h
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_AVERAGE_H
+#define _LINUX_AVERAGE_H
+
+#include <linux/bug.h>
+#include <linux/compiler.h>
+#include <linux/log2.h>
+
+/*
+ * Exponentially weighted moving average (EWMA)
+ *
+ * This implements a fixed-precision EWMA algorithm, with both the
+ * precision and fall-off coefficient determined at compile-time
+ * and built into the generated helper funtions.
+ *
+ * The first argument to the macro is the name that will be used
+ * for the struct and helper functions.
+ *
+ * The second argument, the precision, expresses how many bits are
+ * used for the fractional part of the fixed-precision values.
+ *
+ * The third argument, the weight reciprocal, determines how the
+ * new values will be weighed vs. the old state, new values will
+ * get weight 1/weight_rcp and old values 1-1/weight_rcp. Note
+ * that this parameter must be a power of two for efficiency.
+ */
+
+#define DECLARE_EWMA(name, _precision, _weight_rcp) \
+ struct ewma_##name { \
+ unsigned long internal; \
+ }; \
+ static inline void ewma_##name##_init(struct ewma_##name *e) \
+ { \
+ BUILD_BUG_ON(!__builtin_constant_p(_precision)); \
+ BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp)); \
+ /* \
+ * Even if you want to feed it just 0/1 you should have \
+ * some bits for the non-fractional part... \
+ */ \
+ BUILD_BUG_ON((_precision) > 30); \
+ BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp); \
+ e->internal = 0; \
+ } \
+ static inline unsigned long \
+ ewma_##name##_read(struct ewma_##name *e) \
+ { \
+ BUILD_BUG_ON(!__builtin_constant_p(_precision)); \
+ BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp)); \
+ BUILD_BUG_ON((_precision) > 30); \
+ BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp); \
+ return e->internal >> (_precision); \
+ } \
+ static inline void ewma_##name##_add(struct ewma_##name *e, \
+ unsigned long val) \
+ { \
+ unsigned long internal = READ_ONCE(e->internal); \
+ unsigned long weight_rcp = ilog2(_weight_rcp); \
+ unsigned long precision = _precision; \
+ \
+ BUILD_BUG_ON(!__builtin_constant_p(_precision)); \
+ BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp)); \
+ BUILD_BUG_ON((_precision) > 30); \
+ BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp); \
+ \
+ WRITE_ONCE(e->internal, internal ? \
+ (((internal << weight_rcp) - internal) + \
+ (val << precision)) >> weight_rcp : \
+ (val << precision)); \
+ }
+
+#endif /* _LINUX_AVERAGE_H */