112 lines
3.2 KiB
C
112 lines
3.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
/*
|
|
* Emulate 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 callback 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_HARD);
|
|
/*
|
|
* 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_HARD);
|
|
bctimer.function = bc_handler;
|
|
clockevents_register_device(&ce_broadcast_hrtimer);
|
|
}
|