diff options
Diffstat (limited to 'arch/x86/kernel/i8253.c')
| -rw-r--r-- | arch/x86/kernel/i8253.c | 34 |
1 files changed, 33 insertions, 1 deletions
diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c index 6ebe00cb4a3b..cb9852ad6098 100644 --- a/arch/x86/kernel/i8253.c +++ b/arch/x86/kernel/i8253.c @@ -1,3 +1,4 @@ +// SPDX-License-Identifier: GPL-2.0 /* * 8253/PIT functions * @@ -7,6 +8,8 @@ #include <linux/timex.h> #include <linux/i8253.h> +#include <asm/hypervisor.h> +#include <asm/apic.h> #include <asm/hpet.h> #include <asm/time.h> #include <asm/smp.h> @@ -17,10 +20,39 @@ */ struct clock_event_device *global_clock_event; -void __init setup_pit_timer(void) +/* + * 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()) { + /* + * Don't just ignore the PIT. Ensure it's stopped, because + * VMMs otherwise steal CPU time just to pointlessly waggle + * the (masked) IRQ. + */ + scoped_guard(irq) + clockevent_i8253_disable(); + return false; + } clockevent_i8253_init(true); global_clock_event = &i8253_clockevent; + return true; } #ifndef CONFIG_X86_64 |