1*4882a593Smuzhiyun /* SPDX-License-Identifier: GPL-2.0 */ 2*4882a593Smuzhiyun /* 3*4882a593Smuzhiyun * Copyright (C) 1995-2004 Russell King 4*4882a593Smuzhiyun * 5*4882a593Smuzhiyun * Delay routines, using a pre-computed "loops_per_second" value. 6*4882a593Smuzhiyun */ 7*4882a593Smuzhiyun #ifndef __ASM_ARM_DELAY_H 8*4882a593Smuzhiyun #define __ASM_ARM_DELAY_H 9*4882a593Smuzhiyun 10*4882a593Smuzhiyun #include <asm/memory.h> 11*4882a593Smuzhiyun #include <asm/param.h> /* HZ */ 12*4882a593Smuzhiyun 13*4882a593Smuzhiyun /* 14*4882a593Smuzhiyun * Loop (or tick) based delay: 15*4882a593Smuzhiyun * 16*4882a593Smuzhiyun * loops = loops_per_jiffy * jiffies_per_sec * delay_us / us_per_sec 17*4882a593Smuzhiyun * 18*4882a593Smuzhiyun * where: 19*4882a593Smuzhiyun * 20*4882a593Smuzhiyun * jiffies_per_sec = HZ 21*4882a593Smuzhiyun * us_per_sec = 1000000 22*4882a593Smuzhiyun * 23*4882a593Smuzhiyun * Therefore the constant part is HZ / 1000000 which is a small 24*4882a593Smuzhiyun * fractional number. To make this usable with integer math, we 25*4882a593Smuzhiyun * scale up this constant by 2^31, perform the actual multiplication, 26*4882a593Smuzhiyun * and scale the result back down by 2^31 with a simple shift: 27*4882a593Smuzhiyun * 28*4882a593Smuzhiyun * loops = (loops_per_jiffy * delay_us * UDELAY_MULT) >> 31 29*4882a593Smuzhiyun * 30*4882a593Smuzhiyun * where: 31*4882a593Smuzhiyun * 32*4882a593Smuzhiyun * UDELAY_MULT = 2^31 * HZ / 1000000 33*4882a593Smuzhiyun * = (2^31 / 1000000) * HZ 34*4882a593Smuzhiyun * = 2147.483648 * HZ 35*4882a593Smuzhiyun * = 2147 * HZ + 483648 * HZ / 1000000 36*4882a593Smuzhiyun * 37*4882a593Smuzhiyun * 31 is the biggest scale shift value that won't overflow 32 bits for 38*4882a593Smuzhiyun * delay_us * UDELAY_MULT assuming HZ <= 1000 and delay_us <= 2000. 39*4882a593Smuzhiyun */ 40*4882a593Smuzhiyun #define MAX_UDELAY_MS 2 41*4882a593Smuzhiyun #define UDELAY_MULT UL(2147 * HZ + 483648 * HZ / 1000000) 42*4882a593Smuzhiyun #define UDELAY_SHIFT 31 43*4882a593Smuzhiyun 44*4882a593Smuzhiyun #ifndef __ASSEMBLY__ 45*4882a593Smuzhiyun 46*4882a593Smuzhiyun struct delay_timer { 47*4882a593Smuzhiyun unsigned long (*read_current_timer)(void); 48*4882a593Smuzhiyun unsigned long freq; 49*4882a593Smuzhiyun }; 50*4882a593Smuzhiyun 51*4882a593Smuzhiyun extern struct arm_delay_ops { 52*4882a593Smuzhiyun void (*delay)(unsigned long); 53*4882a593Smuzhiyun void (*const_udelay)(unsigned long); 54*4882a593Smuzhiyun void (*udelay)(unsigned long); 55*4882a593Smuzhiyun unsigned long ticks_per_jiffy; 56*4882a593Smuzhiyun } arm_delay_ops; 57*4882a593Smuzhiyun 58*4882a593Smuzhiyun #define __delay(n) arm_delay_ops.delay(n) 59*4882a593Smuzhiyun 60*4882a593Smuzhiyun /* 61*4882a593Smuzhiyun * This function intentionally does not exist; if you see references to 62*4882a593Smuzhiyun * it, it means that you're calling udelay() with an out of range value. 63*4882a593Smuzhiyun * 64*4882a593Smuzhiyun * With currently imposed limits, this means that we support a max delay 65*4882a593Smuzhiyun * of 2000us. Further limits: HZ<=1000 66*4882a593Smuzhiyun */ 67*4882a593Smuzhiyun extern void __bad_udelay(void); 68*4882a593Smuzhiyun 69*4882a593Smuzhiyun /* 70*4882a593Smuzhiyun * division by multiplication: you don't have to worry about 71*4882a593Smuzhiyun * loss of precision. 72*4882a593Smuzhiyun * 73*4882a593Smuzhiyun * Use only for very small delays ( < 2 msec). Should probably use a 74*4882a593Smuzhiyun * lookup table, really, as the multiplications take much too long with 75*4882a593Smuzhiyun * short delays. This is a "reasonable" implementation, though (and the 76*4882a593Smuzhiyun * first constant multiplications gets optimized away if the delay is 77*4882a593Smuzhiyun * a constant) 78*4882a593Smuzhiyun */ 79*4882a593Smuzhiyun #define __udelay(n) arm_delay_ops.udelay(n) 80*4882a593Smuzhiyun #define __const_udelay(n) arm_delay_ops.const_udelay(n) 81*4882a593Smuzhiyun 82*4882a593Smuzhiyun #define udelay(n) \ 83*4882a593Smuzhiyun (__builtin_constant_p(n) ? \ 84*4882a593Smuzhiyun ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \ 85*4882a593Smuzhiyun __const_udelay((n) * UDELAY_MULT)) : \ 86*4882a593Smuzhiyun __udelay(n)) 87*4882a593Smuzhiyun 88*4882a593Smuzhiyun /* Loop-based definitions for assembly code. */ 89*4882a593Smuzhiyun extern void __loop_delay(unsigned long loops); 90*4882a593Smuzhiyun extern void __loop_udelay(unsigned long usecs); 91*4882a593Smuzhiyun extern void __loop_const_udelay(unsigned long); 92*4882a593Smuzhiyun 93*4882a593Smuzhiyun /* Delay-loop timer registration. */ 94*4882a593Smuzhiyun #define ARCH_HAS_READ_CURRENT_TIMER 95*4882a593Smuzhiyun extern void register_current_timer_delay(const struct delay_timer *timer); 96*4882a593Smuzhiyun 97*4882a593Smuzhiyun #endif /* __ASSEMBLY__ */ 98*4882a593Smuzhiyun 99*4882a593Smuzhiyun #endif /* defined(_ARM_DELAY_H) */ 100*4882a593Smuzhiyun 101