1 // SPDX-License-Identifier: GPL-2.0 1
2 /*
3 * 8253/PIT functions
4 *
5 */
6 #include <linux/clockchips.h>
7 #include <linux/init.h>
8 #include <linux/timex.h>
9 #include <linux/i8253.h>
10
11 #include <asm/hypervisor.h>
12 #include <asm/apic.h>
13 #include <asm/hpet.h>
14 #include <asm/time.h>
15 #include <asm/smp.h>
16
17 /*
18 * HPET replaces the PIT, when enabled. So we
19 * the two timers is used
20 */
21 struct clock_event_device *global_clock_event;
22
23 /*
24 * Modern chipsets can disable the PIT clock w
25 * would be possible to enable the clock but t
26 * specific and not discoverable. Avoid the wh
27 *
28 * These platforms have discoverable TSC/CPU f
29 * requires to know the local APIC timer frequ
30 * calibrated against the PIT interrupt.
31 */
32 static bool __init use_pit(void)
33 {
34 if (!IS_ENABLED(CONFIG_X86_TSC) || !bo
35 return true;
36
37 /* This also returns true when APIC is
38 return apic_needs_pit();
39 }
40
41 bool __init pit_timer_init(void)
42 {
43 if (!use_pit()) {
44 /*
45 * Don't just ignore the PIT.
46 * VMMs otherwise steal CPU ti
47 * the (masked) IRQ.
48 */
49 clockevent_i8253_disable();
50 return false;
51 }
52 clockevent_i8253_init(true);
53 global_clock_event = &i8253_clockevent
54 return true;
55 }
56
57 #ifndef CONFIG_X86_64
58 static int __init init_pit_clocksource(void)
59 {
60 /*
61 * Several reasons not to register PI
62 *
63 * - On SMP PIT does not scale due to
64 * - when HPET is enabled
65 * - when local APIC timer is active
66 */
67 if (num_possible_cpus() > 1 || is_hpet
68 !clockevent_state_periodic(&i8253_
69 return 0;
70
71 return clocksource_i8253_init();
72 }
73 arch_initcall(init_pit_clocksource);
74 #endif /* !CONFIG_X86_64 */
75
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.