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