LXR linux/arch/parisc/lib/delay.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 *      Precise Delay Loops for parisc
   4 *
   5 *      based on code by:
   6 *      Copyright (C) 1993 Linus Torvalds
   7 *      Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
   8 *      Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
   9 *
  10 *      parisc implementation:
  11 *      Copyright (C) 2013 Helge Deller <deller@gmx.de>
  12 */
  13
  14
  15#include <linux/module.h>
  16#include <linux/preempt.h>
  17#include <linux/init.h>
  18
  19#include <asm/delay.h>
  20#include <asm/special_insns.h>    /* for mfctl() */
  21#include <asm/processor.h> /* for boot_cpu_data */
  22
  23/* CR16 based delay: */
  24static void __cr16_delay(unsigned long __loops)
  25{
  26        /*
  27         * Note: Due to unsigned math, cr16 rollovers shouldn't be
  28         * a problem here. However, on 32 bit, we need to make sure
  29         * we don't pass in too big a value. The current default
  30         * value of MAX_UDELAY_MS should help prevent this.
  31         */
  32        u32 bclock, now, loops = __loops;
  33        int cpu;
  34
  35        preempt_disable();
  36        cpu = smp_processor_id();
  37        bclock = mfctl(16);
  38        for (;;) {
  39                now = mfctl(16);
  40                if ((now - bclock) >= loops)
  41                        break;
  42
  43                /* Allow RT tasks to run */
  44                preempt_enable();
  45                asm volatile("  nop\n");
  46                barrier();
  47                preempt_disable();
  48
  49                /*
  50                 * It is possible that we moved to another CPU, and
  51                 * since CR16's are per-cpu we need to calculate
  52                 * that. The delay must guarantee that we wait "at
  53                 * least" the amount of time. Being moved to another
  54                 * CPU could make the wait longer but we just need to
  55                 * make sure we waited long enough. Rebalance the
  56                 * counter for this CPU.
  57                 */
  58                if (unlikely(cpu != smp_processor_id())) {
  59                        loops -= (now - bclock);
  60                        cpu = smp_processor_id();
  61                        bclock = mfctl(16);
  62                }
  63        }
  64        preempt_enable();
  65}
  66
  67
  68void __udelay(unsigned long usecs)
  69{
  70        __cr16_delay(usecs * ((unsigned long)boot_cpu_data.cpu_hz / 1000000UL));
  71}
  72EXPORT_SYMBOL(__udelay);
  73