1 files changed, 100 insertions, 0 deletions
diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
new file mode 100644
index 000000000..4f80b7237
--- /dev/null
+++ b/arch/arm/include/asm/delay.h
@@ -0,0 +1,100 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 1995-2004 Russell King
+ *
+ * Delay routines, using a pre-computed "loops_per_second" value.
+ */
+#ifndef __ASM_ARM_DELAY_H
+#define __ASM_ARM_DELAY_H
+
+#include <asm/memory.h>
+#include <asm/param.h>	/* HZ */
+
+/*
+ * Loop (or tick) based delay:
+ *
+ * loops = loops_per_jiffy * jiffies_per_sec * delay_us / us_per_sec
+ *
+ * where:
+ *
+ * jiffies_per_sec = HZ
+ * us_per_sec = 1000000
+ *
+ * Therefore the constant part is HZ / 1000000 which is a small
+ * fractional number. To make this usable with integer math, we
+ * scale up this constant by 2^31, perform the actual multiplication,
+ * and scale the result back down by 2^31 with a simple shift:
+ *
+ * loops = (loops_per_jiffy * delay_us * UDELAY_MULT) >> 31
+ *
+ * where:
+ *
+ * UDELAY_MULT = 2^31 * HZ / 1000000
+ *             = (2^31 / 1000000) * HZ
+ *             = 2147.483648 * HZ
+ *             = 2147 * HZ + 483648 * HZ / 1000000
+ *
+ * 31 is the biggest scale shift value that won't overflow 32 bits for
+ * delay_us * UDELAY_MULT assuming HZ <= 1000 and delay_us <= 2000.
+ */
+#define MAX_UDELAY_MS	2
+#define UDELAY_MULT	UL(2147 * HZ + 483648 * HZ / 1000000)
+#define UDELAY_SHIFT	31
+
+#ifndef __ASSEMBLY__
+
+struct delay_timer {
+	unsigned long (*read_current_timer)(void);
+	unsigned long freq;
+};
+
+extern struct arm_delay_ops {
+	void (*delay)(unsigned long);
+	void (*const_udelay)(unsigned long);
+	void (*udelay)(unsigned long);
+	unsigned long ticks_per_jiffy;
+} arm_delay_ops;
+
+#define __delay(n)		arm_delay_ops.delay(n)
+
+/*
+ * This function intentionally does not exist; if you see references to
+ * it, it means that you're calling udelay() with an out of range value.
+ *
+ * With currently imposed limits, this means that we support a max delay
+ * of 2000us. Further limits: HZ<=1000
+ */
+extern void __bad_udelay(void);
+
+/*
+ * division by multiplication: you don't have to worry about
+ * loss of precision.
+ *
+ * Use only for very small delays ( < 2 msec).  Should probably use a
+ * lookup table, really, as the multiplications take much too long with
+ * short delays.  This is a "reasonable" implementation, though (and the
+ * first constant multiplications gets optimized away if the delay is
+ * a constant)
+ */
+#define __udelay(n)		arm_delay_ops.udelay(n)
+#define __const_udelay(n)	arm_delay_ops.const_udelay(n)
+
+#define udelay(n)							\
+	(__builtin_constant_p(n) ?					\
+	  ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :		\
+			__const_udelay((n) * UDELAY_MULT)) :		\
+	  __udelay(n))
+
+/* Loop-based definitions for assembly code. */
+extern void __loop_delay(unsigned long loops);
+extern void __loop_udelay(unsigned long usecs);
+extern void __loop_const_udelay(unsigned long);
+
+/* Delay-loop timer registration. */
+#define ARCH_HAS_READ_CURRENT_TIMER
+extern void register_current_timer_delay(const struct delay_timer *timer);
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* defined(_ARM_DELAY_H) */
+