Quelle  delay.c   Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Delay loops based on the OpenRISC implementation.
 *
 * Copyright (C) 2012 ARM Limited
 *
 * Author: Will Deacon <will.deacon@arm.com>
 */

#include <linux/clocksource.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/timex.h>

/*
 * Default to the loop-based delay implementation.
 */
struct arm_delay_ops arm_delay_ops __ro_after_init = {
 .delay  = __loop_delay,
 .const_udelay = __loop_const_udelay,
 .udelay  = __loop_udelay,
};

static const struct delay_timer *delay_timer;
static bool delay_calibrated;
static u64 delay_res;

int read_current_timer(unsigned long *timer_val)
{
 if (!delay_timer)
  return -ENXIO;

 *timer_val = delay_timer->read_current_timer();
 return 0;
}
EXPORT_SYMBOL_GPL(read_current_timer);

static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
{
 return (cyc * mult) >> shift;
}

static void __timer_delay(unsigned long cycles)
{
 cycles_t start = get_cycles();

 while ((get_cycles() - start) < cycles)
  cpu_relax();
}

static void __timer_const_udelay(unsigned long xloops)
{
 unsigned long long loops = xloops;
 loops *= arm_delay_ops.ticks_per_jiffy;
 __timer_delay(loops >> UDELAY_SHIFT);
}

static void __timer_udelay(unsigned long usecs)
{
 __timer_const_udelay(usecs * UDELAY_MULT);
}

void __init register_current_timer_delay(const struct delay_timer *timer)
{
 u32 new_mult, new_shift;
 u64 res;

 clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
          NSEC_PER_SEC, 3600);
 res = cyc_to_ns(1ULL, new_mult, new_shift);

 if (res > 1000) {
  pr_err("Ignoring delay timer %ps, which has insufficient resolution of %lluns\n",
   timer, res);
  return;
 }

 if (!delay_calibrated && (!delay_res || (res < delay_res))) {
  pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
  delay_timer   = timer;
  lpj_fine   = timer->freq / HZ;
  delay_res   = res;

  /* cpufreq may scale loops_per_jiffy, so keep a private copy */
  arm_delay_ops.ticks_per_jiffy = lpj_fine;
  arm_delay_ops.delay  = __timer_delay;
  arm_delay_ops.const_udelay = __timer_const_udelay;
  arm_delay_ops.udelay  = __timer_udelay;
 } else {
  pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
 }
}

unsigned long calibrate_delay_is_known(void)
{
 delay_calibrated = true;
 return lpj_fine;
}

void calibration_delay_done(void)
{
 delay_calibrated = true;
}