linux/kernel/time/tick-oneshot.c
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   1/*
   2 * linux/kernel/time/tick-oneshot.c
   3 *
   4 * This file contains functions which manage high resolution tick
   5 * related events.
   6 *
   7 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
   8 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
   9 * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
  10 *
  11 * This code is licenced under the GPL version 2. For details see
  12 * kernel-base/COPYING.
  13 */
  14#include <linux/cpu.h>
  15#include <linux/err.h>
  16#include <linux/hrtimer.h>
  17#include <linux/interrupt.h>
  18#include <linux/percpu.h>
  19#include <linux/profile.h>
  20#include <linux/sched.h>
  21#include <linux/tick.h>
  22
  23#include "tick-internal.h"
  24
  25/**
  26 * tick_program_event internal worker function
  27 */
  28int tick_dev_program_event(struct clock_event_device *dev, ktime_t expires,
  29                           int force)
  30{
  31        ktime_t now = ktime_get();
  32        int i;
  33
  34        for (i = 0;;) {
  35                int ret = clockevents_program_event(dev, expires, now);
  36
  37                if (!ret || !force)
  38                        return ret;
  39
  40                /*
  41                 * We tried 2 times to program the device with the given
  42                 * min_delta_ns. If that's not working then we double it
  43                 * and emit a warning.
  44                 */
  45                if (++i > 2) {
  46                        /* Increase the min. delta and try again */
  47                        if (!dev->min_delta_ns)
  48                                dev->min_delta_ns = 5000;
  49                        else
  50                                dev->min_delta_ns += dev->min_delta_ns >> 1;
  51
  52                        printk(KERN_WARNING
  53                               "CE: %s increasing min_delta_ns to %lu nsec\n",
  54                               dev->name ? dev->name : "?",
  55                               dev->min_delta_ns << 1);
  56
  57                        i = 0;
  58                }
  59
  60                now = ktime_get();
  61                expires = ktime_add_ns(now, dev->min_delta_ns);
  62        }
  63}
  64
  65/**
  66 * tick_program_event
  67 */
  68int tick_program_event(ktime_t expires, int force)
  69{
  70        struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
  71
  72        return tick_dev_program_event(dev, expires, force);
  73}
  74
  75/**
  76 * tick_resume_onshot - resume oneshot mode
  77 */
  78void tick_resume_oneshot(void)
  79{
  80        struct tick_device *td = &__get_cpu_var(tick_cpu_device);
  81        struct clock_event_device *dev = td->evtdev;
  82
  83        clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
  84        tick_program_event(ktime_get(), 1);
  85}
  86
  87/**
  88 * tick_setup_oneshot - setup the event device for oneshot mode (hres or nohz)
  89 */
  90void tick_setup_oneshot(struct clock_event_device *newdev,
  91                        void (*handler)(struct clock_event_device *),
  92                        ktime_t next_event)
  93{
  94        newdev->event_handler = handler;
  95        clockevents_set_mode(newdev, CLOCK_EVT_MODE_ONESHOT);
  96        tick_dev_program_event(newdev, next_event, 1);
  97}
  98
  99/**
 100 * tick_switch_to_oneshot - switch to oneshot mode
 101 */
 102int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *))
 103{
 104        struct tick_device *td = &__get_cpu_var(tick_cpu_device);
 105        struct clock_event_device *dev = td->evtdev;
 106
 107        if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT) ||
 108                    !tick_device_is_functional(dev)) {
 109
 110                printk(KERN_INFO "Clockevents: "
 111                       "could not switch to one-shot mode:");
 112                if (!dev) {
 113                        printk(" no tick device\n");
 114                } else {
 115                        if (!tick_device_is_functional(dev))
 116                                printk(" %s is not functional.\n", dev->name);
 117                        else
 118                                printk(" %s does not support one-shot mode.\n",
 119                                       dev->name);
 120                }
 121                return -EINVAL;
 122        }
 123
 124        td->mode = TICKDEV_MODE_ONESHOT;
 125        dev->event_handler = handler;
 126        clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
 127        tick_broadcast_switch_to_oneshot();
 128        return 0;
 129}
 130
 131#ifdef CONFIG_HIGH_RES_TIMERS
 132/**
 133 * tick_init_highres - switch to high resolution mode
 134 *
 135 * Called with interrupts disabled.
 136 */
 137int tick_init_highres(void)
 138{
 139        return tick_switch_to_oneshot(hrtimer_interrupt);
 140}
 141#endif
 142