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/page.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) */ 100 101