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 int bc_shutdown(struct clock_event_device *evt) 22 { 23 /* 24 * Note, we cannot cancel the timer here as we might 25 * run into the following live lock scenario: 26 * 27 * cpu 0 cpu1 28 * lock(broadcast_lock); 29 * hrtimer_interrupt() 30 * bc_handler() 31 * tick_handle_oneshot_broadcast(); 32 * lock(broadcast_lock); 33 * hrtimer_cancel() 34 * wait_for_callback() 35 */ 36 hrtimer_try_to_cancel(&bctimer); 37 return 0; 38 } 39 40 /* 41 * This is called from the guts of the broadcast code when the cpu 42 * which is about to enter idle has the earliest broadcast timer event. 43 */ 44 static int bc_set_next(ktime_t expires, struct clock_event_device *bc) 45 { 46 int bc_moved; 47 /* 48 * We try to cancel the timer first. If the callback is on 49 * flight on some other cpu then we let it handle it. If we 50 * were able to cancel the timer nothing can rearm it as we 51 * own broadcast_lock. 52 * 53 * However we can also be called from the event handler of 54 * ce_broadcast_hrtimer itself when it expires. We cannot 55 * restart the timer because we are in the callback, but we 56 * can set the expiry time and let the callback return 57 * HRTIMER_RESTART. 58 * 59 * Since we are in the idle loop at this point and because 60 * hrtimer_{start/cancel} functions call into tracing, 61 * calls to these functions must be bound within RCU_NONIDLE. 62 */ 63 RCU_NONIDLE({ 64 bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0; 65 if (bc_moved) 66 hrtimer_start(&bctimer, expires, 67 HRTIMER_MODE_ABS_PINNED);}); 68 if (bc_moved) { 69 /* Bind the "device" to the cpu */ 70 bc->bound_on = smp_processor_id(); 71 } else if (bc->bound_on == smp_processor_id()) { 72 hrtimer_set_expires(&bctimer, expires); 73 } 74 return 0; 75 } 76 77 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, 83 .rating = 0, 84 .bound_on = -1, 85 .min_delta_ns = 1, 86 .max_delta_ns = KTIME_MAX, 87 .min_delta_ticks = 1, 88 .max_delta_ticks = ULONG_MAX, 89 .mult = 1, 90 .shift = 0, 91 .cpumask = cpu_all_mask, 92 }; 93 94 static enum hrtimer_restart bc_handler(struct hrtimer *t) 95 { 96 ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer); 97 98 if (clockevent_state_oneshot(&ce_broadcast_hrtimer)) 99 if (ce_broadcast_hrtimer.next_event.tv64 != KTIME_MAX) 100 return HRTIMER_RESTART; 101 102 return HRTIMER_NORESTART; 103 } 104 105 void tick_setup_hrtimer_broadcast(void) 106 { 107 hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 108 bctimer.function = bc_handler; 109 clockevents_register_device(&ce_broadcast_hrtimer); 110 } 111