1 // SPDX-License-Identifier: GPL-2.0
3 * Emulate a local clock event device via a pseudo clock device.
7 #include <linux/hrtimer.h>
8 #include <linux/interrupt.h>
9 #include <linux/percpu.h>
10 #include <linux/profile.h>
11 #include <linux/clockchips.h>
12 #include <linux/sched.h>
13 #include <linux/smp.h>
14 #include <linux/module.h>
16 #include "tick-internal.h"
18 static struct hrtimer bctimer
;
20 static int bc_shutdown(struct clock_event_device
*evt
)
23 * Note, we cannot cancel the timer here as we might
24 * run into the following live lock scenario:
27 * lock(broadcast_lock);
30 * tick_handle_oneshot_broadcast();
31 * lock(broadcast_lock);
35 hrtimer_try_to_cancel(&bctimer
);
40 * This is called from the guts of the broadcast code when the cpu
41 * which is about to enter idle has the earliest broadcast timer event.
43 static int bc_set_next(ktime_t expires
, struct clock_event_device
*bc
)
47 * We try to cancel the timer first. If the callback is on
48 * flight on some other cpu then we let it handle it. If we
49 * were able to cancel the timer nothing can rearm it as we
52 * However we can also be called from the event handler of
53 * ce_broadcast_hrtimer itself when it expires. We cannot
54 * restart the timer because we are in the callback, but we
55 * can set the expiry time and let the callback return
58 * Since we are in the idle loop at this point and because
59 * hrtimer_{start/cancel} functions call into tracing,
60 * calls to these functions must be bound within RCU_NONIDLE.
63 bc_moved
= hrtimer_try_to_cancel(&bctimer
) >= 0;
65 hrtimer_start(&bctimer
, expires
,
66 HRTIMER_MODE_ABS_PINNED
);});
68 /* Bind the "device" to the cpu */
69 bc
->bound_on
= smp_processor_id();
70 } else if (bc
->bound_on
== smp_processor_id()) {
71 hrtimer_set_expires(&bctimer
, expires
);
76 static struct clock_event_device ce_broadcast_hrtimer
= {
78 .set_state_shutdown
= bc_shutdown
,
79 .set_next_ktime
= bc_set_next
,
80 .features
= CLOCK_EVT_FEAT_ONESHOT
|
81 CLOCK_EVT_FEAT_KTIME
|
82 CLOCK_EVT_FEAT_HRTIMER
,
86 .max_delta_ns
= KTIME_MAX
,
88 .max_delta_ticks
= ULONG_MAX
,
91 .cpumask
= cpu_possible_mask
,
94 static enum hrtimer_restart
bc_handler(struct hrtimer
*t
)
96 ce_broadcast_hrtimer
.event_handler(&ce_broadcast_hrtimer
);
98 if (clockevent_state_oneshot(&ce_broadcast_hrtimer
))
99 if (ce_broadcast_hrtimer
.next_event
!= KTIME_MAX
)
100 return HRTIMER_RESTART
;
102 return HRTIMER_NORESTART
;
105 void tick_setup_hrtimer_broadcast(void)
107 hrtimer_init(&bctimer
, CLOCK_MONOTONIC
, HRTIMER_MODE_ABS
);
108 bctimer
.function
= bc_handler
;
109 clockevents_register_device(&ce_broadcast_hrtimer
);