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// SPDX-License-Identifier: GPL-2.0
/*
* 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 != 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);
}
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