6 #include <linux/hpet.h>
12 #include <asm/hpet.h>
17 #define pr_fmt(fmt) "hpet: " fmt
50  * HPET address is set in acpi/boot.c, when an ACPI entry exists
100  * HPET command line enable / disable
119 __setup("hpet=", hpet_setup);
134  * is_hpet_enabled - Check whether the legacy HPET timer interrupt is enabled
184  * When the HPET driver (/dev/hpet) is enabled, we need to reserve
235 		/* Associate the first unused channel to /dev/hpet */  in hpet_select_device_channel()
248 /* Common HPET functions */
316 	 * HPET on AMD 81xx needs a second write (with HPET_TN_SETVAL  in hpet_clkevt_set_state_periodic()
378 	 * delayed internally up to two HPET clock cycles in certain  in hpet_clkevt_set_next_event()
421 	 * Start HPET with the boot CPU's cpumask and make it global after  in hpet_legacy_clockevent_register()
425 	strscpy(hc->name, "hpet", sizeof(hc->name));  in hpet_legacy_clockevent_register()
431 	 * Legacy horrors and sins from the past. HPET used periodic mode  in hpet_legacy_clockevent_register()
438 	 *    the next interrupt is not delivered despite the HPET channel  in hpet_legacy_clockevent_register()
439 	 *    being programmed correctly. Reprogramming the HPET after  in hpet_legacy_clockevent_register()
446 	 *    stage makes if hang because the HPET does not get  in hpet_legacy_clockevent_register()
449 	 * Both issues require major surgery and especially the kick HPET  in hpet_legacy_clockevent_register()
451 	 * This 'assume periodic works' magic has survived since HPET  in hpet_legacy_clockevent_register()
461 	/* Start HPET legacy interrupts */  in hpet_legacy_clockevent_register()
471  * HPET MSI Support
506 	.name = "HPET-MSI",
571 		hpet_msi_controller.name = "IR-HPET-MSI";  in hpet_create_irq_domain()
621 		pr_info("Spurious interrupt HPET channel %d\n", hc->num);  in hpet_msi_interrupt_handler()
720 		/* Only consider HPET channel with MSI support */  in hpet_select_clockevents()
724 		sprintf(hc->name, "hpet%d", i);  in hpet_select_clockevents()
755  * Reading the HPET counter is a very slow operation. If a large number of
756  * CPUs are trying to access the HPET counter simultaneously, it can cause
758  * happen when HPET is the default clock source instead of TSC. For a
763  * If multiple CPUs are trying to access the HPET counter at the same time,
771  * The lock and the HPET value are stored together and can be read in a
783 static union hpet_lock hpet __cacheline_aligned = {
795 	 * Read HPET directly if in NMI.  in read_hpet()
801 	 * Read the current state of the lock and HPET value atomically.  in read_hpet()
803 	old.lockval = READ_ONCE(hpet.lockval);  in read_hpet()
809 	if (arch_spin_trylock(&hpet.lock)) {  in read_hpet()
814 		WRITE_ONCE(hpet.value, new.value);  in read_hpet()
815 		arch_spin_unlock(&hpet.lock);  in read_hpet()
825 	 * Wait until the HPET value change or the lock is free to indicate  in read_hpet()
829 	 * HPET value while the lock holder was in the process of releasing  in read_hpet()
831 	 * the value immediately instead of waiting for the next HPET reader  in read_hpet()
836 		new.lockval = READ_ONCE(hpet.lockval);  in read_hpet()
852 	.name		= "hpet",
862  * HPET emulation to provide proper frequency setting.
864  * On such systems the SMM code is initialized with the first HPET register
868  * HPET is up and running before we proceed any further.
870  * A counting loop is safe, as the HPET access takes thousands of CPU cycles.
884 	pr_warn("Config register invalid. Disabling HPET\n");  in hpet_cfg_working()
909 	pr_warn("Counter not counting. HPET disabled\n");  in hpet_counting()
931  * Check whether the system supports PC10. If so force disable HPET as that
939  * That's perfectly fine. HPET is a piece of hardware designed by committee
944  * If HPET is functional it is useful for calibrating TSC, but this can be
949  * In theory HPET support should be removed altogether, but there are older
978 		pr_warn("HPET force enabled via command line, but dysfunctional in PC10.\n");  in hpet_is_pc10_damaged()
982 	pr_info("HPET dysfunctional in PC10. Force disabled.\n");  in hpet_is_pc10_damaged()
988  * hpet_enable - Try to setup the HPET timer. Returns 1 on success.
1024 	 * Read the HPET ID register to retrieve the IRQ routing  in hpet_enable()
1030 	/* This is the HPET channel number which is zero based */  in hpet_enable()
1042 		pr_warn("Disabling HPET.\n");  in hpet_enable()
1108  * which might have detected a system on which the HPET can be enforced.
1110  * Also, the MSI machinery is not working yet when the HPET is initialized
1113  * If the HPET is enabled, then:
1115  *  1) Reserve one channel for /dev/hpet if CONFIG_HPET=y
1117  *  3) Setup /dev/hpet if CONFIG_HPET=y
1143 	ret = cpuhp_setup_state(CPUHP_AP_X86_HPET_ONLINE, "x86/hpet:online",  in hpet_late_init()
1147 	ret = cpuhp_setup_state(CPUHP_X86_HPET_DEAD, "x86/hpet:dead", NULL,  in hpet_late_init()
1176 	/* If the HPET was enabled at boot time, reenable it */  in hpet_disable()
1184  * HPET in LegacyReplacement mode eats up the RTC interrupt line. When HPET
1222  * Check that the HPET counter c1 is ahead of c2
1261  * is not supported by all HPET implementations for channel 1.
1314  * Return 0 if HPET is not being used.