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

   1/*
   2 *      Precise Delay Loops for parisc
   3 *
   4 *      based on code by:
   5 *      Copyright (C) 1993 Linus Torvalds
   6 *      Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
   7 *      Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
   8 *
   9 *      parisc implementation:
  10 *      Copyright (C) 2013 Helge Deller <deller@gmx.de>
  11 */
  12
  13
  14#include <linux/module.h>
  15#include <linux/preempt.h>
  16#include <linux/init.h>
  17
  18#include <asm/processor.h>
  19#include <asm/delay.h>
  20
  21#include <asm/special_insns.h>    /* for mfctl() */
  22#include <asm/processor.h> /* for boot_cpu_data */
  23
  24/* CR16 based delay: */
  25static void __cr16_delay(unsigned long __loops)
  26{
  27        /*
  28         * Note: Due to unsigned math, cr16 rollovers shouldn't be
  29         * a problem here. However, on 32 bit, we need to make sure
  30         * we don't pass in too big a value. The current default
  31         * value of MAX_UDELAY_MS should help prevent this.
  32         */
  33        u32 bclock, now, loops = __loops;
  34        int cpu;
  35
  36        preempt_disable();
  37        cpu = smp_processor_id();
  38        bclock = mfctl(16);
  39        for (;;) {
  40                now = mfctl(16);
  41                if ((now - bclock) >= loops)
  42                        break;
  43
  44                /* Allow RT tasks to run */
  45                preempt_enable();
  46                asm volatile("  nop\n");
  47                barrier();
  48                preempt_disable();
  49
  50                /*
  51                 * It is possible that we moved to another CPU, and
  52                 * since CR16's are per-cpu we need to calculate
  53                 * that. The delay must guarantee that we wait "at
  54                 * least" the amount of time. Being moved to another
  55                 * CPU could make the wait longer but we just need to
  56                 * make sure we waited long enough. Rebalance the
  57                 * counter for this CPU.
  58                 */
  59                if (unlikely(cpu != smp_processor_id())) {
  60                        loops -= (now - bclock);
  61                        cpu = smp_processor_id();
  62                        bclock = mfctl(16);
  63                }
  64        }
  65        preempt_enable();
  66}
  67
  68
  69void __udelay(unsigned long usecs)
  70{
  71        __cr16_delay(usecs * ((unsigned long)boot_cpu_data.cpu_hz / 1000000UL));
  72}
  73EXPORT_SYMBOL(__udelay);
  74