| Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame^] | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
| 2 | /* |
| 3 | * Copyright (C) 1995-2004 Russell King |
| 4 | * |
| 5 | * Delay routines, using a pre-computed "loops_per_second" value. |
| 6 | */ |
| 7 | #ifndef __ASM_ARM_DELAY_H |
| 8 | #define __ASM_ARM_DELAY_H |
| 9 | |
| 10 | #include <asm/memory.h> |
| 11 | #include <asm/param.h> /* HZ */ |
| 12 | |
| 13 | /* |
| 14 | * Loop (or tick) based delay: |
| 15 | * |
| 16 | * loops = loops_per_jiffy * jiffies_per_sec * delay_us / us_per_sec |
| 17 | * |
| 18 | * where: |
| 19 | * |
| 20 | * jiffies_per_sec = HZ |
| 21 | * us_per_sec = 1000000 |
| 22 | * |
| 23 | * Therefore the constant part is HZ / 1000000 which is a small |
| 24 | * fractional number. To make this usable with integer math, we |
| 25 | * scale up this constant by 2^31, perform the actual multiplication, |
| 26 | * and scale the result back down by 2^31 with a simple shift: |
| 27 | * |
| 28 | * loops = (loops_per_jiffy * delay_us * UDELAY_MULT) >> 31 |
| 29 | * |
| 30 | * where: |
| 31 | * |
| 32 | * UDELAY_MULT = 2^31 * HZ / 1000000 |
| 33 | * = (2^31 / 1000000) * HZ |
| 34 | * = 2147.483648 * HZ |
| 35 | * = 2147 * HZ + 483648 * HZ / 1000000 |
| 36 | * |
| 37 | * 31 is the biggest scale shift value that won't overflow 32 bits for |
| 38 | * delay_us * UDELAY_MULT assuming HZ <= 1000 and delay_us <= 2000. |
| 39 | */ |
| 40 | #define MAX_UDELAY_MS 2 |
| 41 | #define UDELAY_MULT UL(2147 * HZ + 483648 * HZ / 1000000) |
| 42 | #define UDELAY_SHIFT 31 |
| 43 | |
| 44 | #ifndef __ASSEMBLY__ |
| 45 | |
| 46 | struct delay_timer { |
| 47 | unsigned long (*read_current_timer)(void); |
| 48 | unsigned long freq; |
| 49 | }; |
| 50 | |
| 51 | extern struct arm_delay_ops { |
| 52 | void (*delay)(unsigned long); |
| 53 | void (*const_udelay)(unsigned long); |
| 54 | void (*udelay)(unsigned long); |
| 55 | unsigned long ticks_per_jiffy; |
| 56 | } arm_delay_ops; |
| 57 | |
| 58 | #define __delay(n) arm_delay_ops.delay(n) |
| 59 | |
| 60 | /* |
| 61 | * This function intentionally does not exist; if you see references to |
| 62 | * it, it means that you're calling udelay() with an out of range value. |
| 63 | * |
| 64 | * With currently imposed limits, this means that we support a max delay |
| 65 | * of 2000us. Further limits: HZ<=1000 |
| 66 | */ |
| 67 | extern void __bad_udelay(void); |
| 68 | |
| 69 | /* |
| 70 | * division by multiplication: you don't have to worry about |
| 71 | * loss of precision. |
| 72 | * |
| 73 | * Use only for very small delays ( < 2 msec). Should probably use a |
| 74 | * lookup table, really, as the multiplications take much too long with |
| 75 | * short delays. This is a "reasonable" implementation, though (and the |
| 76 | * first constant multiplications gets optimized away if the delay is |
| 77 | * a constant) |
| 78 | */ |
| 79 | #define __udelay(n) arm_delay_ops.udelay(n) |
| 80 | #define __const_udelay(n) arm_delay_ops.const_udelay(n) |
| 81 | |
| 82 | #define udelay(n) \ |
| 83 | (__builtin_constant_p(n) ? \ |
| 84 | ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \ |
| 85 | __const_udelay((n) * UDELAY_MULT)) : \ |
| 86 | __udelay(n)) |
| 87 | |
| 88 | /* Loop-based definitions for assembly code. */ |
| 89 | extern void __loop_delay(unsigned long loops); |
| 90 | extern void __loop_udelay(unsigned long usecs); |
| 91 | extern void __loop_const_udelay(unsigned long); |
| 92 | |
| 93 | /* Delay-loop timer registration. */ |
| 94 | #define ARCH_HAS_READ_CURRENT_TIMER |
| 95 | extern void register_current_timer_delay(const struct delay_timer *timer); |
| 96 | |
| 97 | #endif /* __ASSEMBLY__ */ |
| 98 | |
| 99 | #endif /* defined(_ARM_DELAY_H) */ |
| 100 | |