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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)
{
/*
* This is called either from enter/exit idle code or from the
* broadcast handler. In all cases tick_broadcast_lock is held.
*
* hrtimer_cancel() cannot be called here neither from the
* broadcast handler nor from the enter/exit idle code. The idle
* code can run into the problem described in bc_shutdown() and the
* broadcast handler cannot wait for itself to complete for obvious
* reasons.
*
* Each caller tries to arm the hrtimer on its own CPU, but if the
* hrtimer callbback function is currently running, then
* hrtimer_start() cannot move it and the timer stays on the CPU on
* which it is assigned at the moment.
*
* As this can be called from idle code, the hrtimer_start()
* invocation has to be wrapped with RCU_NONIDLE() as
* hrtimer_start() can call into tracing.
*/
RCU_NONIDLE( {
hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED);
/*
* The core tick broadcast mode expects bc->bound_on to be set
* correctly to prevent a CPU which has the broadcast hrtimer
* armed from going deep idle.
*
* As tick_broadcast_lock is held, nothing can change the cpu
* base which was just established in hrtimer_start() above. So
* the below access is safe even without holding the hrtimer
* base lock.
*/
bc->bound_on = bctimer.base->cpu_base->cpu;
} );
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_possible_mask,
};
static enum hrtimer_restart bc_handler(struct hrtimer *t)
{
ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
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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