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 void bc_set_mode(enum clock_event_mode mode, 22 struct clock_event_device *bc) 23 { 24 switch (mode) { 25 case CLOCK_EVT_MODE_SHUTDOWN: 26 /* 27 * Note, we cannot cancel the timer here as we might 28 * run into the following live lock scenario: 29 * 30 * cpu 0 cpu1 31 * lock(broadcast_lock); 32 * hrtimer_interrupt() 33 * bc_handler() 34 * tick_handle_oneshot_broadcast(); 35 * lock(broadcast_lock); 36 * hrtimer_cancel() 37 * wait_for_callback() 38 */ 39 hrtimer_try_to_cancel(&bctimer); 40 break; 41 default: 42 break; 43 } 44 } 45 46 /* 47 * This is called from the guts of the broadcast code when the cpu 48 * which is about to enter idle has the earliest broadcast timer event. 49 */ 50 static int bc_set_next(ktime_t expires, struct clock_event_device *bc) 51 { 52 int bc_moved; 53 /* 54 * We try to cancel the timer first. If the callback is on 55 * flight on some other cpu then we let it handle it. If we 56 * were able to cancel the timer nothing can rearm it as we 57 * own broadcast_lock. 58 * 59 * However we can also be called from the event handler of 60 * ce_broadcast_hrtimer itself when it expires. We cannot 61 * restart the timer because we are in the callback, but we 62 * can set the expiry time and let the callback return 63 * HRTIMER_RESTART. 64 * 65 * Since we are in the idle loop at this point and because 66 * hrtimer_{start/cancel} functions call into tracing, 67 * calls to these functions must be bound within RCU_NONIDLE. 68 */ 69 RCU_NONIDLE(bc_moved = (hrtimer_try_to_cancel(&bctimer) >= 0) ? 70 !hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED) : 71 0); 72 if (bc_moved) { 73 /* Bind the "device" to the cpu */ 74 bc->bound_on = smp_processor_id(); 75 } else if (bc->bound_on == smp_processor_id()) { 76 hrtimer_set_expires(&bctimer, expires); 77 } 78 return 0; 79 } 80 81 static struct clock_event_device ce_broadcast_hrtimer = { 82 .set_mode = bc_set_mode, 83 .set_next_ktime = bc_set_next, 84 .features = CLOCK_EVT_FEAT_ONESHOT | 85 CLOCK_EVT_FEAT_KTIME | 86 CLOCK_EVT_FEAT_HRTIMER, 87 .rating = 0, 88 .bound_on = -1, 89 .min_delta_ns = 1, 90 .max_delta_ns = KTIME_MAX, 91 .min_delta_ticks = 1, 92 .max_delta_ticks = ULONG_MAX, 93 .mult = 1, 94 .shift = 0, 95 .cpumask = cpu_all_mask, 96 }; 97 98 static enum hrtimer_restart bc_handler(struct hrtimer *t) 99 { 100 ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer); 101 102 if (ce_broadcast_hrtimer.next_event.tv64 == KTIME_MAX) 103 return HRTIMER_NORESTART; 104 105 return HRTIMER_RESTART; 106 } 107 108 void tick_setup_hrtimer_broadcast(void) 109 { 110 hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 111 bctimer.function = bc_handler; 112 clockevents_register_device(&ce_broadcast_hrtimer); 113 } 114