| 1 |
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| 2 | |
| 3 | * Copyright (C) 1995-2004 Russell King
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| 4 | *
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| 5 | * Delay routines, using a pre-computed "loops_per_second" value.
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| 6 |
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| 7 | #ifndef __ASM_ARM_DELAY_H
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| 8 | #define __ASM_ARM_DELAY_H
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| 9 |
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| 10 | #include <asm/page.h>
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| 11 | #include <asm/param.h>
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| 12 |
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| 13 | |
| 14 | * Loop (or tick) based delay:
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| 15 | *
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| 16 | * loops = loops_per_jiffy * jiffies_per_sec * delay_us / us_per_sec
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| 17 | *
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| 18 | * where:
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| 19 | *
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| 20 | * jiffies_per_sec = HZ
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| 21 | * us_per_sec = 1000000
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| 22 | *
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| 23 | * Therefore the constant part is HZ / 1000000 which is a small
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| 24 | * fractional number. To make this usable with integer math, we
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| 25 | * scale up this constant by 2^31, perform the actual multiplication,
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| 26 | * and scale the result back down by 2^31 with a simple shift:
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| 27 | *
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| 28 | * loops = (loops_per_jiffy * delay_us * UDELAY_MULT) >> 31
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| 29 | *
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| 30 | * where:
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| 31 | *
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| 32 | * UDELAY_MULT = 2^31 * HZ / 1000000
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| 33 | * = (2^31 / 1000000) * HZ
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| 34 | * = 2147.483648 * HZ
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| 35 | * = 2147 * HZ + 483648 * HZ / 1000000
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| 36 | *
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| 37 | * 31 is the biggest scale shift value that won't overflow 32 bits for
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| 38 | * delay_us * UDELAY_MULT assuming HZ <= 1000 and delay_us <= 2000.
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| 39 |
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| 40 | #define MAX_UDELAY_MS 2
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| 41 | #define UDELAY_MULT UL(2147 * HZ + 483648 * HZ / 1000000)
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| 42 | #define UDELAY_SHIFT 31
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| 43 |
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| 44 | #ifndef __ASSEMBLY__
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| 45 |
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| 46 | struct delay_timer {
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| 47 | unsigned long (*read_current_timer)(void);
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| 48 | unsigned long freq;
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| 49 | };
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| 50 |
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| 51 | extern struct arm_delay_ops {
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| 52 | void (*delay)(unsigned long);
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| 53 | void (*const_udelay)(unsigned long);
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| 54 | void (*udelay)(unsigned long);
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| 55 | unsigned long ticks_per_jiffy;
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| 56 | } arm_delay_ops;
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| 57 |
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| 58 | #define __delay(n) arm_delay_ops.delay(n)
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| 59 |
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| 60 | |
| 61 | * This function intentionally does not exist; if you see references to
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| 62 | * it, it means that you're calling udelay() with an out of range value.
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| 63 | *
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| 64 | * With currently imposed limits, this means that we support a max delay
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| 65 | * of 2000us. Further limits: HZ<=1000
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| 66 |
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| 67 | extern void __bad_udelay(void);
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| 68 |
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| 69 | |
| 70 | * division by multiplication: you don't have to worry about
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| 71 | * loss of precision.
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| 72 | *
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| 73 | * Use only for very small delays ( < 2 msec). Should probably use a
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| 74 | * lookup table, really, as the multiplications take much too long with
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| 75 | * short delays. This is a "reasonable" implementation, though (and the
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| 76 | * first constant multiplications gets optimized away if the delay is
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| 77 | * a constant)
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| 78 |
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| 79 | #define __udelay(n) arm_delay_ops.udelay(n)
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| 80 | #define __const_udelay(n) arm_delay_ops.const_udelay(n)
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| 81 |
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| 82 | #define udelay(n) \
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| 83 | (__builtin_constant_p(n) ? \
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| 84 | ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \
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| 85 | __const_udelay((n) * UDELAY_MULT)) : \
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| 86 | __udelay(n))
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| 87 |
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| 88 |
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| 89 | extern void __loop_delay(unsigned long loops);
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| 90 | extern void __loop_udelay(unsigned long usecs);
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| 91 | extern void __loop_const_udelay(unsigned long);
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| 92 |
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| 93 |
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| 94 | extern void register_current_timer_delay(const struct delay_timer *timer);
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| 95 |
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| 96 | #endif
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| 97 |
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| 98 | #endif
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| 99 |
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