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67 lines
1.6 KiB
67 lines
1.6 KiB
// 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/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 (!IS_ENABLED(CONFIG_X86_TSC) || !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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return false; |
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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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