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Ingo Molnar
5c75b98aa9
Now that the Kconfig space always enables CONFIG_X86_TSC (on x86), remove !CONFIG_X86_TSC code from the x86 arch code. We still keep the Kconfig option to catch any eventual code still pending in maintainer or non-mainline trees, plus some drivers have raw TSC timestamping hacks that use CONFIG_X86_TSC. It's also still possible to disable TSC support runtime. Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Arnd Bergmann <arnd@arndb.de> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ahmed S . Darwish <darwi@linutronix.de> Cc: Andrew Cooper <andrew.cooper3@citrix.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: H . Peter Anvin <hpa@zytor.com> Cc: John Ogness <john.ogness@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Link: https://lore.kernel.org/r/20250425084216.3913608-13-mingo@kernel.org
76 lines
1.8 KiB
C
76 lines
1.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* 8253/PIT functions
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*
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*/
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#include <linux/clockchips.h>
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#include <linux/init.h>
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#include <linux/timex.h>
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#include <linux/i8253.h>
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#include <asm/hypervisor.h>
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#include <asm/apic.h>
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#include <asm/hpet.h>
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#include <asm/time.h>
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#include <asm/smp.h>
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/*
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* HPET replaces the PIT, when enabled. So we need to know, which of
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* the two timers is used
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*/
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struct clock_event_device *global_clock_event;
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/*
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* Modern chipsets can disable the PIT clock which makes it unusable. It
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* would be possible to enable the clock but the registers are chipset
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* specific and not discoverable. Avoid the whack a mole game.
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*
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* These platforms have discoverable TSC/CPU frequencies but this also
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* requires to know the local APIC timer frequency as it normally is
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* calibrated against the PIT interrupt.
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*/
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static bool __init use_pit(void)
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{
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if (!boot_cpu_has(X86_FEATURE_TSC))
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return true;
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/* This also returns true when APIC is disabled */
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return apic_needs_pit();
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}
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bool __init pit_timer_init(void)
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{
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if (!use_pit()) {
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/*
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* Don't just ignore the PIT. Ensure it's stopped, because
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* VMMs otherwise steal CPU time just to pointlessly waggle
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* the (masked) IRQ.
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*/
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scoped_guard(irq)
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clockevent_i8253_disable();
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return false;
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}
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clockevent_i8253_init(true);
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global_clock_event = &i8253_clockevent;
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return true;
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}
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#ifndef CONFIG_X86_64
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static int __init init_pit_clocksource(void)
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{
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/*
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* Several reasons not to register PIT as a clocksource:
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*
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* - On SMP PIT does not scale due to i8253_lock
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* - when HPET is enabled
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* - when local APIC timer is active (PIT is switched off)
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*/
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if (num_possible_cpus() > 1 || is_hpet_enabled() ||
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!clockevent_state_periodic(&i8253_clockevent))
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return 0;
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return clocksource_i8253_init();
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}
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arch_initcall(init_pit_clocksource);
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#endif /* !CONFIG_X86_64 */
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