1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Emulate a local clock event device via a pseudo clock device. 4 */ 5 #include <linux/cpu.h> 6 #include <linux/err.h> 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> 15 16 #include "tick-internal.h" 17 18 static struct hrtimer bctimer; 19 20 static int bc_shutdown(struct clock_event_device *evt) 21 { 22 /* 23 * Note, we cannot cancel the timer here as we might 24 * run into the following live lock scenario: 25 * 26 * cpu 0 cpu1 27 * lock(broadcast_lock); 28 * hrtimer_interrupt() 29 * bc_handler() 30 * tick_handle_oneshot_broadcast(); 31 * lock(broadcast_lock); 32 * hrtimer_cancel() 33 * wait_for_callback() 34 */ 35 hrtimer_try_to_cancel(&bctimer); 36 return 0; 37 } 38 39 /* 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. 42 */ 43 static int bc_set_next(ktime_t expires, struct clock_event_device *bc) 44 { 45 /* 46 * This is called either from enter/exit idle code or from the 47 * broadcast handler. In all cases tick_broadcast_lock is held. 48 * 49 * hrtimer_cancel() cannot be called here neither from the 50 * broadcast handler nor from the enter/exit idle code. The idle 51 * code can run into the problem described in bc_shutdown() and the 52 * broadcast handler cannot wait for itself to complete for obvious 53 * reasons. 54 * 55 * Each caller tries to arm the hrtimer on its own CPU, but if the 56 * hrtimer callback function is currently running, then 57 * hrtimer_start() cannot move it and the timer stays on the CPU on 58 * which it is assigned at the moment. 59 */ 60 hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED_HARD); 61 /* 62 * The core tick broadcast mode expects bc->bound_on to be set 63 * correctly to prevent a CPU which has the broadcast hrtimer 64 * armed from going deep idle. 65 * 66 * As tick_broadcast_lock is held, nothing can change the cpu 67 * base which was just established in hrtimer_start() above. So 68 * the below access is safe even without holding the hrtimer 69 * base lock. 70 */ 71 bc->bound_on = bctimer.base->cpu_base->cpu; 72 73 return 0; 74 } 75 76 static struct clock_event_device ce_broadcast_hrtimer = { 77 .name = "bc_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_possible_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 return HRTIMER_NORESTART; 99 } 100 101 void tick_setup_hrtimer_broadcast(void) 102 { 103 hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD); 104 bctimer.function = bc_handler; 105 clockevents_register_device(&ce_broadcast_hrtimer); 106 } 107