[mirror_ubuntu-bionic-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 void bc_set_mode(enum clock_event_mode mode,
			struct clock_event_device *bc)
{
	switch (mode) {
	case CLOCK_EVT_MODE_SHUTDOWN:
		/*
		 * 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);
		break;
	default:
		break;
	}
}

/*
 * 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)
{
	/*
	 * 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.
	 */
	if (hrtimer_try_to_cancel(&bctimer) >= 0) {
		hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED);
		/* 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 = {
	.set_mode		= bc_set_mode,
	.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 (ce_broadcast_hrtimer.next_event.tv64 == KTIME_MAX)
		return HRTIMER_NORESTART;

	return HRTIMER_RESTART;
}

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
	21	static void bc_set_mode(enum clock_event_mode mode,
	22	struct clock_event_device *bc)
	23	{
	24	switch (mode) {
	25	case CLOCK_EVT_MODE_SHUTDOWN:
	26	/*
	27	* Note, we cannot cancel the timer here as we might
	28	* run into the following live lock scenario:
	29	*
	30	* cpu 0 cpu1
	31	* lock(broadcast_lock);
	32	* hrtimer_interrupt()
	33	* bc_handler()
	34	* tick_handle_oneshot_broadcast();
	35	* lock(broadcast_lock);
	36	* hrtimer_cancel()
	37	* wait_for_callback()
	38	*/
	39	hrtimer_try_to_cancel(&bctimer);
	40	break;
	41	default:
	42	break;
	43	}
	44	}
	45
	46	/*
	47	* This is called from the guts of the broadcast code when the cpu
	48	* which is about to enter idle has the earliest broadcast timer event.
	49	*/
	50	static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
	51	{
	52	/*
	53	* We try to cancel the timer first. If the callback is on
	54	* flight on some other cpu then we let it handle it. If we
	55	* were able to cancel the timer nothing can rearm it as we
	56	* own broadcast_lock.
	57	*
	58	* However we can also be called from the event handler of
	59	* ce_broadcast_hrtimer itself when it expires. We cannot
	60	* restart the timer because we are in the callback, but we
	61	* can set the expiry time and let the callback return
	62	* HRTIMER_RESTART.
	63	*/
	64	if (hrtimer_try_to_cancel(&bctimer) >= 0) {
65	hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED);
66	/* Bind the "device" to the cpu */
67	bc->bound_on = smp_processor_id();
68	} else if (bc->bound_on == smp_processor_id()) {
69	hrtimer_set_expires(&bctimer, expires);
70	}
71	return 0;
72	}
73
74	static struct clock_event_device ce_broadcast_hrtimer = {
75	.set_mode = bc_set_mode,
76	.set_next_ktime = bc_set_next,
77	.features = CLOCK_EVT_FEAT_ONESHOT \|
78	CLOCK_EVT_FEAT_KTIME \|
79	CLOCK_EVT_FEAT_HRTIMER,
80	.rating = 0,
81	.bound_on = -1,
82	.min_delta_ns = 1,
83	.max_delta_ns = KTIME_MAX,
84	.min_delta_ticks = 1,
849401b6	85	.max_delta_ticks = ULONG_MAX,
5d1638ac PM	86	.mult = 1,
	87	.shift = 0,
	88	.cpumask = cpu_all_mask,
	89	};
	90
	91	static enum hrtimer_restart bc_handler(struct hrtimer *t)
	92	{
	93	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
	94
	95	if (ce_broadcast_hrtimer.next_event.tv64 == KTIME_MAX)
	96	return HRTIMER_NORESTART;
	97
	98	return HRTIMER_RESTART;
	99	}
	100
	101	void tick_setup_hrtimer_broadcast(void)
	102	{
	103	hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
	104	bctimer.function = bc_handler;
	105	clockevents_register_device(&ce_broadcast_hrtimer);
	106	}