cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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i8253.c (1669B)

      1// SPDX-License-Identifier: GPL-2.0
      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/apic.h>
     12#include <asm/hpet.h>
     13#include <asm/time.h>
     14#include <asm/smp.h>
     15
     16/*
     17 * HPET replaces the PIT, when enabled. So we need to know, which of
     18 * the two timers is used
     19 */
     20struct clock_event_device *global_clock_event;
     21
     22/*
     23 * Modern chipsets can disable the PIT clock which makes it unusable. It
     24 * would be possible to enable the clock but the registers are chipset
     25 * specific and not discoverable. Avoid the whack a mole game.
     26 *
     27 * These platforms have discoverable TSC/CPU frequencies but this also
     28 * requires to know the local APIC timer frequency as it normally is
     29 * calibrated against the PIT interrupt.
     30 */
     31static bool __init use_pit(void)
     32{
     33	if (!IS_ENABLED(CONFIG_X86_TSC) || !boot_cpu_has(X86_FEATURE_TSC))
     34		return true;
     35
     36	/* This also returns true when APIC is disabled */
     37	return apic_needs_pit();
     38}
     39
     40bool __init pit_timer_init(void)
     41{
     42	if (!use_pit())
     43		return false;
     44
     45	clockevent_i8253_init(true);
     46	global_clock_event = &i8253_clockevent;
     47	return true;
     48}
     49
     50#ifndef CONFIG_X86_64
     51static int __init init_pit_clocksource(void)
     52{
     53	 /*
     54	  * Several reasons not to register PIT as a clocksource:
     55	  *
     56	  * - On SMP PIT does not scale due to i8253_lock
     57	  * - when HPET is enabled
     58	  * - when local APIC timer is active (PIT is switched off)
     59	  */
     60	if (num_possible_cpus() > 1 || is_hpet_enabled() ||
     61	    !clockevent_state_periodic(&i8253_clockevent))
     62		return 0;
     63
     64	return clocksource_i8253_init();
     65}
     66arch_initcall(init_pit_clocksource);
     67#endif /* !CONFIG_X86_64 */