cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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delay.h (2903B)

      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
     46struct delay_timer {
     47	unsigned long (*read_current_timer)(void);
     48	unsigned long freq;
     49};
     50
     51extern 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 */
     67extern 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. */
     89extern void __loop_delay(unsigned long loops);
     90extern void __loop_udelay(unsigned long usecs);
     91extern void __loop_const_udelay(unsigned long);
     92
     93/* Delay-loop timer registration. */
     94#define ARCH_HAS_READ_CURRENT_TIMER
     95extern void register_current_timer_delay(const struct delay_timer *timer);
     96
     97#endif /* __ASSEMBLY__ */
     98
     99#endif /* defined(_ARM_DELAY_H) */
    100