[mirror_ubuntu-artful-kernel.git] / kernel / time / tick-broadcast-hrtimer.c

/*
 * linux/kernel/time/tick-broadcast-hrtimer.c
 * This file emulates a local clock event device
 * via a pseudo clock device.
 */
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/profile.h>
#include <linux/clockchips.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/module.h>

#include "tick-internal.h"

static struct hrtimer bctimer;

static int bc_shutdown(struct clock_event_device *evt)
{
	/*
	 * Note, we cannot cancel the timer here as we might
	 * run into the following live lock scenario:
	 *
	 * cpu 0		cpu1
	 * lock(broadcast_lock);
	 *			hrtimer_interrupt()
	 *			bc_handler()
	 *			   tick_handle_oneshot_broadcast();
	 *			    lock(broadcast_lock);
	 * hrtimer_cancel()
	 *  wait_for_callback()
	 */
	hrtimer_try_to_cancel(&bctimer);
	return 0;
}

/*
 * This is called from the guts of the broadcast code when the cpu
 * which is about to enter idle has the earliest broadcast timer event.
 */
static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
{
	int bc_moved;
	/*
	 * We try to cancel the timer first. If the callback is on
	 * flight on some other cpu then we let it handle it. If we
	 * were able to cancel the timer nothing can rearm it as we
	 * own broadcast_lock.
	 *
	 * However we can also be called from the event handler of
	 * ce_broadcast_hrtimer itself when it expires. We cannot
	 * restart the timer because we are in the callback, but we
	 * can set the expiry time and let the callback return
	 * HRTIMER_RESTART.
	 *
	 * Since we are in the idle loop at this point and because
	 * hrtimer_{start/cancel} functions call into tracing,
	 * calls to these functions must be bound within RCU_NONIDLE.
	 */
	RCU_NONIDLE({
			bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0;
			if (bc_moved)
				hrtimer_start(&bctimer, expires,
					      HRTIMER_MODE_ABS_PINNED);});
	if (bc_moved) {
		/* Bind the "device" to the cpu */
		bc->bound_on = smp_processor_id();
	} else if (bc->bound_on == smp_processor_id()) {
		hrtimer_set_expires(&bctimer, expires);
	}
	return 0;
}

static struct clock_event_device ce_broadcast_hrtimer = {
	.name			= "bc_hrtimer",
	.set_state_shutdown	= bc_shutdown,
	.set_next_ktime		= bc_set_next,
	.features		= CLOCK_EVT_FEAT_ONESHOT |
				  CLOCK_EVT_FEAT_KTIME |
				  CLOCK_EVT_FEAT_HRTIMER,
	.rating			= 0,
	.bound_on		= -1,
	.min_delta_ns		= 1,
	.max_delta_ns		= KTIME_MAX,
	.min_delta_ticks	= 1,
	.max_delta_ticks	= ULONG_MAX,
	.mult			= 1,
	.shift			= 0,
	.cpumask		= cpu_all_mask,
};

static enum hrtimer_restart bc_handler(struct hrtimer *t)
{
	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);

	if (clockevent_state_oneshot(&ce_broadcast_hrtimer))
		if (ce_broadcast_hrtimer.next_event.tv64 != KTIME_MAX)
			return HRTIMER_RESTART;

	return HRTIMER_NORESTART;
}

void tick_setup_hrtimer_broadcast(void)
{
	hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
	bctimer.function = bc_handler;
	clockevents_register_device(&ce_broadcast_hrtimer);
}
Commit	Line	Data
5d1638ac PM	1	/*
	2	* linux/kernel/time/tick-broadcast-hrtimer.c
	3	* This file emulates a local clock event device
	4	* via a pseudo clock device.
	5	*/
	6	#include <linux/cpu.h>
	7	#include <linux/err.h>
	8	#include <linux/hrtimer.h>
	9	#include <linux/interrupt.h>
	10	#include <linux/percpu.h>
	11	#include <linux/profile.h>
	12	#include <linux/clockchips.h>
	13	#include <linux/sched.h>
	14	#include <linux/smp.h>
	15	#include <linux/module.h>
	16
	17	#include "tick-internal.h"
	18
	19	static struct hrtimer bctimer;
	20
ecbebcb8	21	static int bc_shutdown(struct clock_event_device *evt)
5d1638ac	22	{
ecbebcb8 VK	23	/*
	24	* Note, we cannot cancel the timer here as we might
	25	* run into the following live lock scenario:
	26	*
	27	* cpu 0 cpu1
	28	* lock(broadcast_lock);
	29	* hrtimer_interrupt()
	30	* bc_handler()
	31	* tick_handle_oneshot_broadcast();
	32	* lock(broadcast_lock);
	33	* hrtimer_cancel()
	34	* wait_for_callback()
	35	*/
	36	hrtimer_try_to_cancel(&bctimer);
	37	return 0;
5d1638ac PM	38	}
	39
	40	/*
	41	* This is called from the guts of the broadcast code when the cpu
	42	* which is about to enter idle has the earliest broadcast timer event.
	43	*/
	44	static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
	45	{
a127d2bc	46	int bc_moved;
5d1638ac PM	47	/*
	48	* We try to cancel the timer first. If the callback is on
	49	* flight on some other cpu then we let it handle it. If we
	50	* were able to cancel the timer nothing can rearm it as we
	51	* own broadcast_lock.
	52	*
	53	* However we can also be called from the event handler of
	54	* ce_broadcast_hrtimer itself when it expires. We cannot
	55	* restart the timer because we are in the callback, but we
	56	* can set the expiry time and let the callback return
	57	* HRTIMER_RESTART.
a127d2bc PM	58	*
	59	* Since we are in the idle loop at this point and because
	60	* hrtimer_{start/cancel} functions call into tracing,
	61	* calls to these functions must be bound within RCU_NONIDLE.
5d1638ac	62	*/
b8a62f1f TG	63	RCU_NONIDLE({
	64	bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0;
	65	if (bc_moved)
	66	hrtimer_start(&bctimer, expires,
	67	HRTIMER_MODE_ABS_PINNED);});
a127d2bc	68	if (bc_moved) {
5d1638ac PM	69	/* Bind the "device" to the cpu */
	70	bc->bound_on = smp_processor_id();
	71	} else if (bc->bound_on == smp_processor_id()) {
	72	hrtimer_set_expires(&bctimer, expires);
	73	}
	74	return 0;
	75	}
	76
	77	static struct clock_event_device ce_broadcast_hrtimer = {
51302137	78	.name = "bc_hrtimer",
ecbebcb8	79	.set_state_shutdown = bc_shutdown,
5d1638ac PM	80	.set_next_ktime = bc_set_next,
	81	.features = CLOCK_EVT_FEAT_ONESHOT \|
	82	CLOCK_EVT_FEAT_KTIME \|
	83	CLOCK_EVT_FEAT_HRTIMER,
	84	.rating = 0,
	85	.bound_on = -1,
	86	.min_delta_ns = 1,
	87	.max_delta_ns = KTIME_MAX,
	88	.min_delta_ticks = 1,
849401b6	89	.max_delta_ticks = ULONG_MAX,
5d1638ac PM	90	.mult = 1,
	91	.shift = 0,
	92	.cpumask = cpu_all_mask,
	93	};
	94
	95	static enum hrtimer_restart bc_handler(struct hrtimer *t)
	96	{
	97	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
	98
ecbebcb8	99	if (clockevent_state_oneshot(&ce_broadcast_hrtimer))
38d23a6c AS	100	if (ce_broadcast_hrtimer.next_event.tv64 != KTIME_MAX)
38d23a6c AS	101	return HRTIMER_RESTART;
ecbebcb8 VK	102
ecbebcb8 VK	103	return HRTIMER_NORESTART;
5d1638ac PM	104	}
	105
	106	void tick_setup_hrtimer_broadcast(void)
	107	{
	108	hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
	109	bctimer.function = bc_handler;
	110	clockevents_register_device(&ce_broadcast_hrtimer);
	111	}