clockevents_program_min

#ifdef CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST
 
/* Limit min_delta to a jiffie */
#define MIN_DELTA_LIMIT     (NSEC_PER_SEC / HZ)
 
/**
 * clockevents_increase_min_delta - raise minimum delta of a clock event device
 * @dev:       device to increase the minimum delta
 *
 * Returns 0 on success, -ETIME when the minimum delta reached the limit.
 */
static int clockevents_increase_min_delta(struct clock_event_device *dev)
{
    /* Nothing to do if we already reached the limit */
    if (dev->min_delta_ns >= MIN_DELTA_LIMIT) {
        printk_deferred(KERN_WARNING
                "CE: Reprogramming failure. Giving up\n");
        dev->next_event = KTIME_MAX;
        return -ETIME;
    }
 
    if (dev->min_delta_ns < 5000)
        dev->min_delta_ns = 5000;
    else
        dev->min_delta_ns += dev->min_delta_ns >> 1;
 
    if (dev->min_delta_ns > MIN_DELTA_LIMIT)
        dev->min_delta_ns = MIN_DELTA_LIMIT;
 
    printk_deferred(KERN_WARNING
            "CE: %s increased min_delta_ns to %llu nsec\n",
            dev->name ? dev->name : "?",
            (unsigned long long) dev->min_delta_ns);
    return 0;
}
 
/**
 * clockevents_program_min_delta - Set clock event device to the minimum delay.
 * @dev:    device to program
 *
 * Returns 0 on success, -ETIME when the retry loop failed.
 */
static int clockevents_program_min_delta(struct clock_event_device *dev)
{
    unsigned long long clc;
    int64_t delta;
    int i;
 
    for (i = 0;;) {
        delta = dev->min_delta_ns;
        dev->next_event = ktime_add_ns(ktime_get(), delta);
 
        if (clockevent_state_shutdown(dev))
            return 0;
 
        dev->retries++;
        clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
        if (dev->set_next_event((unsigned long) clc, dev) == 0)
            return 0;
 
        if (++i > 2) {
            /*
             * We tried 3 times to program the device with the
             * given min_delta_ns. Try to increase the minimum
             * delta, if that fails as well get out of here.
             */
            if (clockevents_increase_min_delta(dev))
                return -ETIME;
            i = 0;
        }
    }
}
 
#else  /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */
 
/**
 * clockevents_program_min_delta - Set clock event device to the minimum delay.
 * @dev:    device to program
 *
 * Returns 0 on success, -ETIME when the retry loop failed.
 */
static int clockevents_program_min_delta(struct clock_event_device *dev)
{
    unsigned long long clc;
    int64_t delta = 0;
    int i;
 
    for (i = 0; i < 10; i++) {
        delta += dev->min_delta_ns;
        dev->next_event = ktime_add_ns(ktime_get(), delta);
 
        if (clockevent_state_shutdown(dev))
            return 0;
 
        dev->retries++;
        clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
        if (dev->set_next_event((unsigned long) clc, dev) == 0)
            return 0;
    }
    return -ETIME;
}
函数源码
