6 #include <linux/hpet.h>
11 #include <asm/hpet.h>
16 #define pr_fmt(fmt) "hpet: " fmt
49  * HPET address is set in acpi/boot.c, when an ACPI entry exists
99  * HPET command line enable / disable
118 __setup("hpet=", hpet_setup);
133  * is_hpet_enabled - Check whether the legacy HPET timer interrupt is enabled
183  * When the HPET driver (/dev/hpet) is enabled, we need to reserve
234 		/* Associate the first unused channel to /dev/hpet */  in hpet_select_device_channel()
247 /* Common HPET functions */
315 	 * HPET on AMD 81xx needs a second write (with HPET_TN_SETVAL  in hpet_clkevt_set_state_periodic()
377 	 * delayed internally up to two HPET clock cycles in certain  in hpet_clkevt_set_next_event()
420 	 * Start HPET with the boot CPU's cpumask and make it global after  in hpet_legacy_clockevent_register()
424 	strscpy(hc->name, "hpet", sizeof(hc->name));  in hpet_legacy_clockevent_register()
430 	 * Legacy horrors and sins from the past. HPET used periodic mode  in hpet_legacy_clockevent_register()
437 	 *    the next interrupt is not delivered despite the HPET channel  in hpet_legacy_clockevent_register()
438 	 *    being programmed correctly. Reprogramming the HPET after  in hpet_legacy_clockevent_register()
445 	 *    stage makes if hang because the HPET does not get  in hpet_legacy_clockevent_register()
448 	 * Both issues require major surgery and especially the kick HPET  in hpet_legacy_clockevent_register()
450 	 * This 'assume periodic works' magic has survived since HPET  in hpet_legacy_clockevent_register()
460 	/* Start HPET legacy interrupts */  in hpet_legacy_clockevent_register()
470  * HPET MSI Support
505 	.name = "HPET-MSI",
578 		hpet_msi_controller.name = "IR-HPET-MSI";  in hpet_create_irq_domain()
628 		pr_info("Spurious interrupt HPET channel %d\n", hc->num);  in hpet_msi_interrupt_handler()
727 		/* Only consider HPET channel with MSI support */  in hpet_select_clockevents()
731 		sprintf(hc->name, "hpet%d", i);  in hpet_select_clockevents()
762  * Reading the HPET counter is a very slow operation. If a large number of
763  * CPUs are trying to access the HPET counter simultaneously, it can cause
765  * happen when HPET is the default clock source instead of TSC. For a
770  * If multiple CPUs are trying to access the HPET counter at the same time,
778  * The lock and the HPET value are stored together and can be read in a
790 static union hpet_lock hpet __cacheline_aligned = {
802 	 * Read HPET directly if in NMI.  in read_hpet()
808 	 * Read the current state of the lock and HPET value atomically.  in read_hpet()
810 	old.lockval = READ_ONCE(hpet.lockval);  in read_hpet()
816 	if (arch_spin_trylock(&hpet.lock)) {  in read_hpet()
821 		WRITE_ONCE(hpet.value, new.value);  in read_hpet()
822 		arch_spin_unlock(&hpet.lock);  in read_hpet()
832 	 * Wait until the HPET value change or the lock is free to indicate  in read_hpet()
836 	 * HPET value while the lock holder was in the process of releasing  in read_hpet()
838 	 * the value immediately instead of waiting for the next HPET reader  in read_hpet()
843 		new.lockval = READ_ONCE(hpet.lockval);  in read_hpet()
859 	.name		= "hpet",
869  * HPET emulation to provide proper frequency setting.
871  * On such systems the SMM code is initialized with the first HPET register
875  * HPET is up and running before we proceed any further.
877  * A counting loop is safe, as the HPET access takes thousands of CPU cycles.
891 	pr_warn("Config register invalid. Disabling HPET\n");  in hpet_cfg_working()
916 	pr_warn("Counter not counting. HPET disabled\n");  in hpet_counting()
941  * Check whether the system supports PC10. If so force disable HPET as that
949  * That's perfectly fine. HPET is a piece of hardware designed by committee
954  * If HPET is functional it is useful for calibrating TSC, but this can be
959  * In theory HPET support should be removed altogether, but there are older
988 		pr_warn("HPET force enabled via command line, but dysfunctional in PC10.\n");  in hpet_is_pc10_damaged()
992 	pr_info("HPET dysfunctional in PC10. Force disabled.\n");  in hpet_is_pc10_damaged()
998  * hpet_enable - Try to setup the HPET timer. Returns 1 on success.
1034 	 * Read the HPET ID register to retrieve the IRQ routing  in hpet_enable()
1040 	/* This is the HPET channel number which is zero based */  in hpet_enable()
1052 		pr_warn("Disabling HPET.\n");  in hpet_enable()
1118  * which might have detected a system on which the HPET can be enforced.
1120  * Also, the MSI machinery is not working yet when the HPET is initialized
1123  * If the HPET is enabled, then:
1125  *  1) Reserve one channel for /dev/hpet if CONFIG_HPET=y
1127  *  3) Setup /dev/hpet if CONFIG_HPET=y
1153 	ret = cpuhp_setup_state(CPUHP_AP_X86_HPET_ONLINE, "x86/hpet:online",  in hpet_late_init()
1157 	ret = cpuhp_setup_state(CPUHP_X86_HPET_DEAD, "x86/hpet:dead", NULL,  in hpet_late_init()
1186 	/* If the HPET was enabled at boot time, reenable it */  in hpet_disable()
1194  * HPET in LegacyReplacement mode eats up the RTC interrupt line. When HPET
1232  * Check that the HPET counter c1 is ahead of c2
1271  * is not supported by all HPET implementations for channel 1.
1324  * Return 0 if HPET is not being used.