[PATCH v2 1/4] drm/etnaviv: add simple moving average (SMA)

[Christian Gmeiner <christian.gmeiner@gmail.com>]

This adds a SMA algorithm inspired by Exponentially weighted moving
average (EWMA) algorithm found in the kernel.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
---
 drivers/gpu/drm/etnaviv/etnaviv_sma.h | 53 +++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 drivers/gpu/drm/etnaviv/etnaviv_sma.h

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_sma.h b/drivers/gpu/drm/etnaviv/etnaviv_sma.h
new file mode 100644
index 000000000000..81564d5cbdc3
--- /dev/null
+++ b/drivers/gpu/drm/etnaviv/etnaviv_sma.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 Etnaviv Project
+ */
+
+#ifndef __ETNAVIV_SMA_H__
+#define __ETNAVIV_SMA_H__
+
+#include <linux/bug.h>
+#include <linux/compiler.h>
+
+/*
+ * Simple moving average (SMA)
+ *
+ * This implements a fixed-size SMA algorithm.
+ *
+ * The first argument to the macro is the name that will be used
+ * for the struct and helper functions.
+ *
+ * The second argument, the samples, expresses how many samples are
+ * used for the SMA algorithm.
+ */
+
+#define DECLARE_SMA(name, _samples) \
+    struct sma_##name { \
+        unsigned long pos; \
+        unsigned long sum; \
+        unsigned long samples[_samples]; \
+    }; \
+    static inline void sma_##name##_init(struct sma_##name *s) \
+    { \
+        BUILD_BUG_ON(!__builtin_constant_p(_samples));	\
+        memset(s, 0, sizeof(struct sma_##name)); \
+    } \
+    static inline unsigned long sma_##name##_read(struct sma_##name *s) \
+    { \
+        BUILD_BUG_ON(!__builtin_constant_p(_samples));	\
+        return s->sum / _samples; \
+    } \
+    static inline void sma_##name##_add(struct sma_##name *s, unsigned long val) \
+    { \
+        unsigned long pos = READ_ONCE(s->pos); \
+        unsigned long sum = READ_ONCE(s->sum); \
+        unsigned long sample = READ_ONCE(s->samples[pos]); \
+      \
+        BUILD_BUG_ON(!__builtin_constant_p(_samples));	\
+      \
+       WRITE_ONCE(s->sum, sum - sample + val); \
+       WRITE_ONCE(s->samples[pos], val); \
+       WRITE_ONCE(s->pos, pos + 1 == _samples ? 0 : pos + 1); \
+    }
+
+#endif /* __ETNAVIV_SMA_H__ */
-- 
2.36.1