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(timer: &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(timer: &bctimer, tim: expires, mode: 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(timer: &bctimer, CLOCK_MONOTONIC, mode: HRTIMER_MODE_ABS_HARD); |
104 | bctimer.function = bc_handler; |
105 | clockevents_register_device(dev: &ce_broadcast_hrtimer); |
106 | } |
107 | |