arch/arm64/lib/delay.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Delay loops based on the OpenRISC implementation.
   4  *
   5  * Copyright (C) 2012 ARM Limited
   6  *
   7  * Author: Will Deacon <will.deacon@arm.com>
   8  */
   9
  10 #include <linux/delay.h>
  11 #include <linux/init.h>
  12 #include <linux/kernel.h>
  13 #include <linux/module.h>
  14 #include <linux/timex.h>
  15
  16 #include <clocksource/arm_arch_timer.h>
  17
  18 #define USECS_TO_CYCLES(time_usecs)                     \
  19         xloops_to_cycles((time_usecs) * 0x10C7UL)
  20
  21 static inline unsigned long xloops_to_cycles(unsigned long xloops)
  22 {
  23         return (xloops * loops_per_jiffy * HZ) >> 32;
  24 }
  25
  26 void __delay(unsigned long cycles)
  27 {
  28         cycles_t start = get_cycles();
  29
  30         if (alternative_has_cap_unlikely(ARM64_HAS_WFXT)) {
  31                 u64 end = start + cycles;
  32
  33                 /*
  34                  * Start with WFIT. If an interrupt makes us resume
  35                  * early, use a WFET loop to complete the delay.
  36                  */
  37                 wfit(end);
  38                 while ((get_cycles() - start) < cycles)
  39                         wfet(end);
  40         } else  if (arch_timer_evtstrm_available()) {
  41                 const cycles_t timer_evt_period =
  42                         USECS_TO_CYCLES(ARCH_TIMER_EVT_STREAM_PERIOD_US);
  43
  44                 while ((get_cycles() - start + timer_evt_period) < cycles)
  45                         wfe();
  46         }
  47
  48         while ((get_cycles() - start) < cycles)
  49                 cpu_relax();
  50 }
  51 EXPORT_SYMBOL(__delay);
  52
  53 inline void __const_udelay(unsigned long xloops)
  54 {
  55         __delay(xloops_to_cycles(xloops));
  56 }
  57 EXPORT_SYMBOL(__const_udelay);
  58
  59 void __udelay(unsigned long usecs)
  60 {
  61         __const_udelay(usecs * 0x10C7UL); /* 2**32 / 1000000 (rounded up) */
  62 }
  63 EXPORT_SYMBOL(__udelay);
  64
  65 void __ndelay(unsigned long nsecs)
  66 {
  67         __const_udelay(nsecs * 0x5UL); /* 2**32 / 1000000000 (rounded up) */
  68 }
  69 EXPORT_SYMBOL(__ndelay);