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