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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
commit | 2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch) | |
tree | 848558de17fb3008cdf4d861b01ac7781903ce39 /arch/x86/kernel/i8253.c | |
parent | Initial commit. (diff) | |
download | linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip |
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'arch/x86/kernel/i8253.c')
-rw-r--r-- | arch/x86/kernel/i8253.c | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c new file mode 100644 index 000000000..2b7999a1a --- /dev/null +++ b/arch/x86/kernel/i8253.c @@ -0,0 +1,67 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * 8253/PIT functions + * + */ +#include <linux/clockchips.h> +#include <linux/init.h> +#include <linux/timex.h> +#include <linux/i8253.h> + +#include <asm/apic.h> +#include <asm/hpet.h> +#include <asm/time.h> +#include <asm/smp.h> + +/* + * 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 */ |