From ace9429bb58fd418f0c81d4c2835699bddf6bde6 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Thu, 11 Apr 2024 10:27:49 +0200 Subject: Adding upstream version 6.6.15. Signed-off-by: Daniel Baumann --- arch/x86/kernel/i8253.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 arch/x86/kernel/i8253.c (limited to 'arch/x86/kernel/i8253.c') diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c new file mode 100644 index 0000000000..2b7999a1a5 --- /dev/null +++ b/arch/x86/kernel/i8253.c @@ -0,0 +1,67 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * 8253/PIT functions + * + */ +#include +#include +#include +#include + +#include +#include +#include +#include + +/* + * HPET replaces the PIT, when enabled. So we need to know, which of + * the two timers is used + */ +struct clock_event_device *global_clock_event; + +/* + * Modern chipsets can disable the PIT clock which makes it unusable. It + * would be possible to enable the clock but the registers are chipset + * specific and not discoverable. Avoid the whack a mole game. + * + * These platforms have discoverable TSC/CPU frequencies but this also + * requires to know the local APIC timer frequency as it normally is + * calibrated against the PIT interrupt. + */ +static bool __init use_pit(void) +{ + if (!IS_ENABLED(CONFIG_X86_TSC) || !boot_cpu_has(X86_FEATURE_TSC)) + return true; + + /* This also returns true when APIC is disabled */ + return apic_needs_pit(); +} + +bool __init pit_timer_init(void) +{ + if (!use_pit()) + return false; + + clockevent_i8253_init(true); + global_clock_event = &i8253_clockevent; + return true; +} + +#ifndef CONFIG_X86_64 +static int __init init_pit_clocksource(void) +{ + /* + * Several reasons not to register PIT as a clocksource: + * + * - On SMP PIT does not scale due to i8253_lock + * - when HPET is enabled + * - when local APIC timer is active (PIT is switched off) + */ + if (num_possible_cpus() > 1 || is_hpet_enabled() || + !clockevent_state_periodic(&i8253_clockevent)) + return 0; + + return clocksource_i8253_init(); +} +arch_initcall(init_pit_clocksource); +#endif /* !CONFIG_X86_64 */ -- cgit v1.2.3