hrtimer_restart, alarm timer

This is a good chance to look into timer mechanism ofkernel timer.

/** * alarmtimer_fired - Handles alarm hrtimer being fired. * @timer: pointer to hrtimer being run * * When a alarm timer fires, this runs through the timerqueue to * see which alarms expired, and runs those. If there are more alarm * timers queued for the future, we set the hrtimer to fire when * when the next future alarm timer expires. */ static enum hrtimer_restart alarmtimer_fired(struct hrtimer *timer) {     struct alarm_base *base = container_of(timer, struct alarm_base, timer);     struct timerqueue_node *next;     unsigned long flags;     ktime_t now;     int ret = HRTIMER_NORESTART;     int restart = ALARMTIMER_NORESTART;       spin_lock_irqsave(&base->lock, flags);     now = base->gettime();     while ((next = timerqueue_getnext(&base->timerqueue))) {         struct alarm *alarm;         ktime_t expired = next->expires;           if (expired.tv64 > now.tv64)             break;           alarm = container_of(next, struct alarm, node);           timerqueue_del(&base->timerqueue, &alarm->node);         alarm->state &= ~ALARMTIMER_STATE_ENQUEUED;           alarm->state |= ALARMTIMER_STATE_CALLBACK;         spin_unlock_irqrestore(&base->lock, flags);         if (alarm->function)             restart = alarm->function(alarm, now);         spin_lock_irqsave(&base->lock, flags);         alarm->state &= ~ALARMTIMER_STATE_CALLBACK;           if (restart != ALARMTIMER_NORESTART) {             timerqueue_add(&base->timerqueue, &alarm->node);             alarm->state |= ALARMTIMER_STATE_ENQUEUED;         }     }       if (next) {         hrtimer_set_expires(&base->timer, next->expires);         ret = HRTIMER_RESTART;     }     spin_unlock_irqrestore(&base->lock, flags);       return ret;   }.

 

This is a good chance to look into timer mechanism ofkernel timer.

 

static long alarm_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {     int rv = 0;     unsigned long flags; <snip> case ANDROID_ALARM_SET_OLD:     case ANDROID_ALARM_SET_AND_WAIT_OLD:         if (get_user(new_alarm_time.tv_sec, (int __user *)arg)) {             rv = -EFAULT;             goto err1;         }         new_alarm_time.tv_nsec = 0;         goto from_old_alarm_set;       case ANDROID_ALARM_SET_AND_WAIT(0):     case ANDROID_ALARM_SET(0):         if (copy_from_user(&new_alarm_time, (void __user *)arg,             sizeof(new_alarm_time))) {             rv = -EFAULT;             goto err1;         } from_old_alarm_set:         spin_lock_irqsave(&alarm_slock, flags);         pr_alarm(IO, "alarm %d set %ld.%09ld\n", alarm_type,             new_alarm_time.tv_sec, new_alarm_time.tv_nsec);         alarm_enabled |= alarm_type_mask;         devalarm_start(&alarms[alarm_type],             timespec_to_ktime(new_alarm_time));         spin_unlock_irqrestore(&alarm_slock, flags);         if (ANDROID_ALARM_BASE_CMD(cmd) != ANDROID_ALARM_SET_AND_WAIT(0)             && cmd != ANDROID_ALARM_SET_AND_WAIT_OLD)             break;         /* fall though */     case ANDROID_ALARM_WAIT:

 

 

static const struct file_operations alarm_fops = {     .owner = THIS_MODULE,     .unlocked_ioctl = alarm_ioctl,     .open = alarm_open,     .release = alarm_release, };

 

This driver is accessible thru “/dev/alarm”.

static struct miscdevice alarm_device = {     .minor = MISC_DYNAMIC_MINOR,     .name = "alarm",     .fops = &alarm_fops, };

 

 

[ 1248.598756 04-23 15:18:45.380] [<c00bccd4>] (alarmtimer_fired+0x144/0x15c) from [<c00970ac>] (__run_hrtimer+0x98/0x304) [ 1248.609786 04-23 15:18:45.380] [<c00970ac>] (__run_hrtimer+0x98/0x304) from [<c0097fb0>] (hrtimer_interrupt+0x134/0x2f0) [ 1248.620908 04-23 15:18:45.380] [<c0097fb0>] (hrtimer_interrupt+0x134/0x2f0) from [<c0028e84>] (tegra_cputimer_interrupt+0x4c/0x54) [ 1248.632924 04-23 15:18:45.380] [<c0028e84>] (tegra_cputimer_interrupt+0x4c/0x54) from [<c00e9450>] (handle_irq_event_percpu+0x78/0x2d8) [ 1248.645365 04-23 15:18:45.380] [<c00e9450>] (handle_irq_event_percpu+0x78/0x2d8) from [<c00e96f4>] (handle_irq_event+0x44/0x64) [ 1248.657087 04-23 15:18:45.380] [<c00e96f4>] (handle_irq_event+0x44/0x64) from [<c00ec480>] (handle_fasteoi_irq+0xc4/0x16c) [ 1248.668375 04-23 15:18:45.380] [<c00ec480>] (handle_fasteoi_irq+0xc4/0x16c) from [<c00e8c6c>] (generic_handle_irq+0x30/0x44) [ 1248.679844 04-23 15:18:45.380] [<c00e8c6c>] (generic_handle_irq+0x30/0x44) from [<c000f074>] (handle_IRQ+0x54/0xb4) [ 1248.690514 04-23 15:18:45.380] [<c000f074>] (handle_IRQ+0x54/0xb4) from [<c00084cc>] (gic_handle_irq+0x2c/0x60) [ 1248.700859 04-23 15:18:45.380] [<c00084cc>] (gic_handle_irq+0x2c/0x60) from [<c081d804>] (__irq_svc+0x44/0x78)

 

static void __run_hrtimer(struct hrtimer *timer, ktime_t *now) {     struct hrtimer_clock_base *base = timer->base;     struct hrtimer_cpu_base *cpu_base = base->cpu_base;     enum hrtimer_restart (*fn)(struct hrtimer *);     int restart;       WARN_ON(!irqs_disabled());       debug_deactivate(timer);     __remove_hrtimer(timer, base, HRTIMER_STATE_CALLBACK, 0);     timer_stats_account_hrtimer(timer);     fn = timer->function; // alarmtimer_fired is called thru this callback function. <snip>