Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1361 insertions, 0 deletions

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
new file mode 100644
index 000000000..574df24a8
--- /dev/null
+++ b/arch/x86/kernel/hpet.c
@@ -0,0 +1,1361 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/clockchips.h>
+#include <linux/interrupt.h>
+#include <linux/export.h>
+#include <linux/delay.h>
+#include <linux/hpet.h>
+#include <linux/cpu.h>
+#include <linux/irq.h>
+
+#include <asm/hpet.h>
+#include <asm/time.h>
+#include <asm/mwait.h>
+
+#undef  pr_fmt
+#define pr_fmt(fmt) "hpet: " fmt
+
+enum hpet_mode {
+	HPET_MODE_UNUSED,
+	HPET_MODE_LEGACY,
+	HPET_MODE_CLOCKEVT,
+	HPET_MODE_DEVICE,
+};
+
+struct hpet_channel {
+	struct clock_event_device	evt;
+	unsigned int			num;
+	unsigned int			cpu;
+	unsigned int			irq;
+	unsigned int			in_use;
+	enum hpet_mode			mode;
+	unsigned int			boot_cfg;
+	char				name[10];
+};
+
+struct hpet_base {
+	unsigned int			nr_channels;
+	unsigned int			nr_clockevents;
+	unsigned int			boot_cfg;
+	struct hpet_channel		*channels;
+};
+
+#define HPET_MASK			CLOCKSOURCE_MASK(32)
+
+#define HPET_MIN_CYCLES			128
+#define HPET_MIN_PROG_DELTA		(HPET_MIN_CYCLES + (HPET_MIN_CYCLES >> 1))
+
+/*
+ * HPET address is set in acpi/boot.c, when an ACPI entry exists
+ */
+unsigned long				hpet_address;
+u8					hpet_blockid; /* OS timer block num */
+bool					hpet_msi_disable;
+
+#ifdef CONFIG_PCI_MSI
+static DEFINE_PER_CPU(struct hpet_channel *, cpu_hpet_channel);
+static struct irq_domain		*hpet_domain;
+#endif
+
+static void __iomem			*hpet_virt_address;
+
+static struct hpet_base			hpet_base;
+
+static bool				hpet_legacy_int_enabled;
+static unsigned long			hpet_freq;
+
+bool					boot_hpet_disable;
+bool					hpet_force_user;
+static bool				hpet_verbose;
+
+static inline
+struct hpet_channel *clockevent_to_channel(struct clock_event_device *evt)
+{
+	return container_of(evt, struct hpet_channel, evt);
+}
+
+inline unsigned int hpet_readl(unsigned int a)
+{
+	return readl(hpet_virt_address + a);
+}
+
+static inline void hpet_writel(unsigned int d, unsigned int a)
+{
+	writel(d, hpet_virt_address + a);
+}
+
+static inline void hpet_set_mapping(void)
+{
+	hpet_virt_address = ioremap(hpet_address, HPET_MMAP_SIZE);
+}
+
+static inline void hpet_clear_mapping(void)
+{
+	iounmap(hpet_virt_address);
+	hpet_virt_address = NULL;
+}
+
+/*
+ * HPET command line enable / disable
+ */
+static int __init hpet_setup(char *str)
+{
+	while (str) {
+		char *next = strchr(str, ',');
+
+		if (next)
+			*next++ = 0;
+		if (!strncmp("disable", str, 7))
+			boot_hpet_disable = true;
+		if (!strncmp("force", str, 5))
+			hpet_force_user = true;
+		if (!strncmp("verbose", str, 7))
+			hpet_verbose = true;
+		str = next;
+	}
+	return 1;
+}
+__setup("hpet=", hpet_setup);
+
+static int __init disable_hpet(char *str)
+{
+	boot_hpet_disable = true;
+	return 1;
+}
+__setup("nohpet", disable_hpet);
+
+static inline int is_hpet_capable(void)
+{
+	return !boot_hpet_disable && hpet_address;
+}
+
+/**
+ * is_hpet_enabled - Check whether the legacy HPET timer interrupt is enabled
+ */
+int is_hpet_enabled(void)
+{
+	return is_hpet_capable() && hpet_legacy_int_enabled;
+}
+EXPORT_SYMBOL_GPL(is_hpet_enabled);
+
+static void _hpet_print_config(const char *function, int line)
+{
+	u32 i, id, period, cfg, status, channels, l, h;
+
+	pr_info("%s(%d):\n", function, line);
+
+	id = hpet_readl(HPET_ID);
+	period = hpet_readl(HPET_PERIOD);
+	pr_info("ID: 0x%x, PERIOD: 0x%x\n", id, period);
+
+	cfg = hpet_readl(HPET_CFG);
+	status = hpet_readl(HPET_STATUS);
+	pr_info("CFG: 0x%x, STATUS: 0x%x\n", cfg, status);
+
+	l = hpet_readl(HPET_COUNTER);
+	h = hpet_readl(HPET_COUNTER+4);
+	pr_info("COUNTER_l: 0x%x, COUNTER_h: 0x%x\n", l, h);
+
+	channels = ((id & HPET_ID_NUMBER) >> HPET_ID_NUMBER_SHIFT) + 1;
+
+	for (i = 0; i < channels; i++) {
+		l = hpet_readl(HPET_Tn_CFG(i));
+		h = hpet_readl(HPET_Tn_CFG(i)+4);
+		pr_info("T%d: CFG_l: 0x%x, CFG_h: 0x%x\n", i, l, h);
+
+		l = hpet_readl(HPET_Tn_CMP(i));
+		h = hpet_readl(HPET_Tn_CMP(i)+4);
+		pr_info("T%d: CMP_l: 0x%x, CMP_h: 0x%x\n", i, l, h);
+
+		l = hpet_readl(HPET_Tn_ROUTE(i));
+		h = hpet_readl(HPET_Tn_ROUTE(i)+4);
+		pr_info("T%d ROUTE_l: 0x%x, ROUTE_h: 0x%x\n", i, l, h);
+	}
+}
+
+#define hpet_print_config()					\
+do {								\
+	if (hpet_verbose)					\
+		_hpet_print_config(__func__, __LINE__);	\
+} while (0)
+
+/*
+ * When the HPET driver (/dev/hpet) is enabled, we need to reserve
+ * timer 0 and timer 1 in case of RTC emulation.
+ */
+#ifdef CONFIG_HPET
+
+static void __init hpet_reserve_platform_timers(void)
+{
+	struct hpet_data hd;
+	unsigned int i;
+
+	memset(&hd, 0, sizeof(hd));
+	hd.hd_phys_address	= hpet_address;
+	hd.hd_address		= hpet_virt_address;
+	hd.hd_nirqs		= hpet_base.nr_channels;
+
+	/*
+	 * NOTE that hd_irq[] reflects IOAPIC input pins (LEGACY_8254
+	 * is wrong for i8259!) not the output IRQ.  Many BIOS writers
+	 * don't bother configuring *any* comparator interrupts.
+	 */
+	hd.hd_irq[0] = HPET_LEGACY_8254;
+	hd.hd_irq[1] = HPET_LEGACY_RTC;
+
+	for (i = 0; i < hpet_base.nr_channels; i++) {
+		struct hpet_channel *hc = hpet_base.channels + i;
+
+		if (i >= 2)
+			hd.hd_irq[i] = hc->irq;
+
+		switch (hc->mode) {
+		case HPET_MODE_UNUSED:
+		case HPET_MODE_DEVICE:
+			hc->mode = HPET_MODE_DEVICE;
+			break;
+		case HPET_MODE_CLOCKEVT:
+		case HPET_MODE_LEGACY:
+			hpet_reserve_timer(&hd, hc->num);
+			break;
+		}
+	}
+
+	hpet_alloc(&hd);
+}
+
+static void __init hpet_select_device_channel(void)
+{
+	int i;
+
+	for (i = 0; i < hpet_base.nr_channels; i++) {
+		struct hpet_channel *hc = hpet_base.channels + i;
+
+		/* Associate the first unused channel to /dev/hpet */
+		if (hc->mode == HPET_MODE_UNUSED) {
+			hc->mode = HPET_MODE_DEVICE;
+			return;
+		}
+	}
+}
+
+#else
+static inline void hpet_reserve_platform_timers(void) { }
+static inline void hpet_select_device_channel(void) {}
+#endif
+
+/* Common HPET functions */
+static void hpet_stop_counter(void)
+{
+	u32 cfg = hpet_readl(HPET_CFG);
+
+	cfg &= ~HPET_CFG_ENABLE;
+	hpet_writel(cfg, HPET_CFG);
+}
+
+static void hpet_reset_counter(void)
+{
+	hpet_writel(0, HPET_COUNTER);
+	hpet_writel(0, HPET_COUNTER + 4);
+}
+
+static void hpet_start_counter(void)
+{
+	unsigned int cfg = hpet_readl(HPET_CFG);
+
+	cfg |= HPET_CFG_ENABLE;
+	hpet_writel(cfg, HPET_CFG);
+}
+
+static void hpet_restart_counter(void)
+{
+	hpet_stop_counter();
+	hpet_reset_counter();
+	hpet_start_counter();
+}
+
+static void hpet_resume_device(void)
+{
+	force_hpet_resume();
+}
+
+static void hpet_resume_counter(struct clocksource *cs)
+{
+	hpet_resume_device();
+	hpet_restart_counter();
+}
+
+static void hpet_enable_legacy_int(void)
+{
+	unsigned int cfg = hpet_readl(HPET_CFG);
+
+	cfg |= HPET_CFG_LEGACY;
+	hpet_writel(cfg, HPET_CFG);
+	hpet_legacy_int_enabled = true;
+}
+
+static int hpet_clkevt_set_state_periodic(struct clock_event_device *evt)
+{
+	unsigned int channel = clockevent_to_channel(evt)->num;
+	unsigned int cfg, cmp, now;
+	uint64_t delta;
+
+	hpet_stop_counter();
+	delta = ((uint64_t)(NSEC_PER_SEC / HZ)) * evt->mult;
+	delta >>= evt->shift;
+	now = hpet_readl(HPET_COUNTER);
+	cmp = now + (unsigned int)delta;
+	cfg = hpet_readl(HPET_Tn_CFG(channel));
+	cfg |= HPET_TN_ENABLE | HPET_TN_PERIODIC | HPET_TN_SETVAL |
+	       HPET_TN_32BIT;
+	hpet_writel(cfg, HPET_Tn_CFG(channel));
+	hpet_writel(cmp, HPET_Tn_CMP(channel));
+	udelay(1);
+	/*
+	 * HPET on AMD 81xx needs a second write (with HPET_TN_SETVAL
+	 * cleared) to T0_CMP to set the period. The HPET_TN_SETVAL
+	 * bit is automatically cleared after the first write.
+	 * (See AMD-8111 HyperTransport I/O Hub Data Sheet,
+	 * Publication # 24674)
+	 */
+	hpet_writel((unsigned int)delta, HPET_Tn_CMP(channel));
+	hpet_start_counter();
+	hpet_print_config();
+
+	return 0;
+}
+
+static int hpet_clkevt_set_state_oneshot(struct clock_event_device *evt)
+{
+	unsigned int channel = clockevent_to_channel(evt)->num;
+	unsigned int cfg;
+
+	cfg = hpet_readl(HPET_Tn_CFG(channel));
+	cfg &= ~HPET_TN_PERIODIC;
+	cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
+	hpet_writel(cfg, HPET_Tn_CFG(channel));
+
+	return 0;
+}
+
+static int hpet_clkevt_set_state_shutdown(struct clock_event_device *evt)
+{
+	unsigned int channel = clockevent_to_channel(evt)->num;
+	unsigned int cfg;
+
+	cfg = hpet_readl(HPET_Tn_CFG(channel));
+	cfg &= ~HPET_TN_ENABLE;
+	hpet_writel(cfg, HPET_Tn_CFG(channel));
+
+	return 0;
+}
+
+static int hpet_clkevt_legacy_resume(struct clock_event_device *evt)
+{
+	hpet_enable_legacy_int();
+	hpet_print_config();
+	return 0;
+}
+
+static int
+hpet_clkevt_set_next_event(unsigned long delta, struct clock_event_device *evt)
+{
+	unsigned int channel = clockevent_to_channel(evt)->num;
+	u32 cnt;
+	s32 res;
+
+	cnt = hpet_readl(HPET_COUNTER);
+	cnt += (u32) delta;
+	hpet_writel(cnt, HPET_Tn_CMP(channel));
+
+	/*
+	 * HPETs are a complete disaster. The compare register is
+	 * based on a equal comparison and neither provides a less
+	 * than or equal functionality (which would require to take
+	 * the wraparound into account) nor a simple count down event
+	 * mode. Further the write to the comparator register is
+	 * delayed internally up to two HPET clock cycles in certain
+	 * chipsets (ATI, ICH9,10). Some newer AMD chipsets have even
+	 * longer delays. We worked around that by reading back the
+	 * compare register, but that required another workaround for
+	 * ICH9,10 chips where the first readout after write can
+	 * return the old stale value. We already had a minimum
+	 * programming delta of 5us enforced, but a NMI or SMI hitting
+	 * between the counter readout and the comparator write can
+	 * move us behind that point easily. Now instead of reading
+	 * the compare register back several times, we make the ETIME
+	 * decision based on the following: Return ETIME if the
+	 * counter value after the write is less than HPET_MIN_CYCLES
+	 * away from the event or if the counter is already ahead of
+	 * the event. The minimum programming delta for the generic
+	 * clockevents code is set to 1.5 * HPET_MIN_CYCLES.
+	 */
+	res = (s32)(cnt - hpet_readl(HPET_COUNTER));
+
+	return res < HPET_MIN_CYCLES ? -ETIME : 0;
+}
+
+static void hpet_init_clockevent(struct hpet_channel *hc, unsigned int rating)
+{
+	struct clock_event_device *evt = &hc->evt;
+
+	evt->rating		= rating;
+	evt->irq		= hc->irq;
+	evt->name		= hc->name;
+	evt->cpumask		= cpumask_of(hc->cpu);
+	evt->set_state_oneshot	= hpet_clkevt_set_state_oneshot;
+	evt->set_next_event	= hpet_clkevt_set_next_event;
+	evt->set_state_shutdown	= hpet_clkevt_set_state_shutdown;
+
+	evt->features = CLOCK_EVT_FEAT_ONESHOT;
+	if (hc->boot_cfg & HPET_TN_PERIODIC) {
+		evt->features		|= CLOCK_EVT_FEAT_PERIODIC;
+		evt->set_state_periodic	= hpet_clkevt_set_state_periodic;
+	}
+}
+
+static void __init hpet_legacy_clockevent_register(struct hpet_channel *hc)
+{
+	/*
+	 * Start HPET with the boot CPU's cpumask and make it global after
+	 * the IO_APIC has been initialized.
+	 */
+	hc->cpu = boot_cpu_data.cpu_index;
+	strncpy(hc->name, "hpet", sizeof(hc->name));
+	hpet_init_clockevent(hc, 50);
+
+	hc->evt.tick_resume	= hpet_clkevt_legacy_resume;
+
+	/*
+	 * Legacy horrors and sins from the past. HPET used periodic mode
+	 * unconditionally forever on the legacy channel 0. Removing the
+	 * below hack and using the conditional in hpet_init_clockevent()
+	 * makes at least Qemu and one hardware machine fail to boot.
+	 * There are two issues which cause the boot failure:
+	 *
+	 * #1 After the timer delivery test in IOAPIC and the IOAPIC setup
+	 *    the next interrupt is not delivered despite the HPET channel
+	 *    being programmed correctly. Reprogramming the HPET after
+	 *    switching to IOAPIC makes it work again. After fixing this,
+	 *    the next issue surfaces:
+	 *
+	 * #2 Due to the unconditional periodic mode availability the Local
+	 *    APIC timer calibration can hijack the global clockevents
+	 *    event handler without causing damage. Using oneshot at this
+	 *    stage makes if hang because the HPET does not get
+	 *    reprogrammed due to the handler hijacking. Duh, stupid me!
+	 *
+	 * Both issues require major surgery and especially the kick HPET
+	 * again after enabling IOAPIC results in really nasty hackery.
+	 * This 'assume periodic works' magic has survived since HPET
+	 * support got added, so it's questionable whether this should be
+	 * fixed. Both Qemu and the failing hardware machine support
+	 * periodic mode despite the fact that both don't advertise it in
+	 * the configuration register and both need that extra kick after
+	 * switching to IOAPIC. Seems to be a feature...
+	 */
+	hc->evt.features		|= CLOCK_EVT_FEAT_PERIODIC;
+	hc->evt.set_state_periodic	= hpet_clkevt_set_state_periodic;
+
+	/* Start HPET legacy interrupts */
+	hpet_enable_legacy_int();
+
+	clockevents_config_and_register(&hc->evt, hpet_freq,
+					HPET_MIN_PROG_DELTA, 0x7FFFFFFF);
+	global_clock_event = &hc->evt;
+	pr_debug("Clockevent registered\n");
+}
+
+/*
+ * HPET MSI Support
+ */
+#ifdef CONFIG_PCI_MSI
+
+void hpet_msi_unmask(struct irq_data *data)
+{
+	struct hpet_channel *hc = irq_data_get_irq_handler_data(data);
+	unsigned int cfg;
+
+	cfg = hpet_readl(HPET_Tn_CFG(hc->num));
+	cfg |= HPET_TN_ENABLE | HPET_TN_FSB;
+	hpet_writel(cfg, HPET_Tn_CFG(hc->num));
+}
+
+void hpet_msi_mask(struct irq_data *data)
+{
+	struct hpet_channel *hc = irq_data_get_irq_handler_data(data);
+	unsigned int cfg;
+
+	cfg = hpet_readl(HPET_Tn_CFG(hc->num));
+	cfg &= ~(HPET_TN_ENABLE | HPET_TN_FSB);
+	hpet_writel(cfg, HPET_Tn_CFG(hc->num));
+}
+
+void hpet_msi_write(struct hpet_channel *hc, struct msi_msg *msg)
+{
+	hpet_writel(msg->data, HPET_Tn_ROUTE(hc->num));
+	hpet_writel(msg->address_lo, HPET_Tn_ROUTE(hc->num) + 4);
+}
+
+static int hpet_clkevt_msi_resume(struct clock_event_device *evt)
+{
+	struct hpet_channel *hc = clockevent_to_channel(evt);
+	struct irq_data *data = irq_get_irq_data(hc->irq);
+	struct msi_msg msg;
+
+	/* Restore the MSI msg and unmask the interrupt */
+	irq_chip_compose_msi_msg(data, &msg);
+	hpet_msi_write(hc, &msg);
+	hpet_msi_unmask(data);
+	return 0;
+}
+
+static irqreturn_t hpet_msi_interrupt_handler(int irq, void *data)
+{
+	struct hpet_channel *hc = data;
+	struct clock_event_device *evt = &hc->evt;
+
+	if (!evt->event_handler) {
+		pr_info("Spurious interrupt HPET channel %d\n", hc->num);
+		return IRQ_HANDLED;
+	}
+
+	evt->event_handler(evt);
+	return IRQ_HANDLED;
+}
+
+static int hpet_setup_msi_irq(struct hpet_channel *hc)
+{
+	if (request_irq(hc->irq, hpet_msi_interrupt_handler,
+			IRQF_TIMER | IRQF_NOBALANCING,
+			hc->name, hc))
+		return -1;
+
+	disable_irq(hc->irq);
+	irq_set_affinity(hc->irq, cpumask_of(hc->cpu));
+	enable_irq(hc->irq);
+
+	pr_debug("%s irq %u for MSI\n", hc->name, hc->irq);
+
+	return 0;
+}
+
+/* Invoked from the hotplug callback on @cpu */
+static void init_one_hpet_msi_clockevent(struct hpet_channel *hc, int cpu)
+{
+	struct clock_event_device *evt = &hc->evt;
+
+	hc->cpu = cpu;
+	per_cpu(cpu_hpet_channel, cpu) = hc;
+	hpet_setup_msi_irq(hc);
+
+	hpet_init_clockevent(hc, 110);
+	evt->tick_resume = hpet_clkevt_msi_resume;
+
+	clockevents_config_and_register(evt, hpet_freq, HPET_MIN_PROG_DELTA,
+					0x7FFFFFFF);
+}
+
+static struct hpet_channel *hpet_get_unused_clockevent(void)
+{
+	int i;
+
+	for (i = 0; i < hpet_base.nr_channels; i++) {
+		struct hpet_channel *hc = hpet_base.channels + i;
+
+		if (hc->mode != HPET_MODE_CLOCKEVT || hc->in_use)
+			continue;
+		hc->in_use = 1;
+		return hc;
+	}
+	return NULL;
+}
+
+static int hpet_cpuhp_online(unsigned int cpu)
+{
+	struct hpet_channel *hc = hpet_get_unused_clockevent();
+
+	if (hc)
+		init_one_hpet_msi_clockevent(hc, cpu);
+	return 0;
+}
+
+static int hpet_cpuhp_dead(unsigned int cpu)
+{
+	struct hpet_channel *hc = per_cpu(cpu_hpet_channel, cpu);
+
+	if (!hc)
+		return 0;
+	free_irq(hc->irq, hc);
+	hc->in_use = 0;
+	per_cpu(cpu_hpet_channel, cpu) = NULL;
+	return 0;
+}
+
+static void __init hpet_select_clockevents(void)
+{
+	unsigned int i;
+
+	hpet_base.nr_clockevents = 0;
+
+	/* No point if MSI is disabled or CPU has an Always Runing APIC Timer */
+	if (hpet_msi_disable || boot_cpu_has(X86_FEATURE_ARAT))
+		return;
+
+	hpet_print_config();
+
+	hpet_domain = hpet_create_irq_domain(hpet_blockid);
+	if (!hpet_domain)
+		return;
+
+	for (i = 0; i < hpet_base.nr_channels; i++) {
+		struct hpet_channel *hc = hpet_base.channels + i;
+		int irq;
+
+		if (hc->mode != HPET_MODE_UNUSED)
+			continue;
+
+		/* Only consider HPET channel with MSI support */
+		if (!(hc->boot_cfg & HPET_TN_FSB_CAP))
+			continue;
+
+		sprintf(hc->name, "hpet%d", i);
+
+		irq = hpet_assign_irq(hpet_domain, hc, hc->num);
+		if (irq <= 0)
+			continue;
+
+		hc->irq = irq;
+		hc->mode = HPET_MODE_CLOCKEVT;
+
+		if (++hpet_base.nr_clockevents == num_possible_cpus())
+			break;
+	}
+
+	pr_info("%d channels of %d reserved for per-cpu timers\n",
+		hpet_base.nr_channels, hpet_base.nr_clockevents);
+}
+
+#else
+
+static inline void hpet_select_clockevents(void) { }
+
+#define hpet_cpuhp_online	NULL
+#define hpet_cpuhp_dead		NULL
+
+#endif
+
+/*
+ * Clock source related code
+ */
+#if defined(CONFIG_SMP) && defined(CONFIG_64BIT)
+/*
+ * Reading the HPET counter is a very slow operation. If a large number of
+ * CPUs are trying to access the HPET counter simultaneously, it can cause
+ * massive delays and slow down system performance dramatically. This may
+ * happen when HPET is the default clock source instead of TSC. For a
+ * really large system with hundreds of CPUs, the slowdown may be so
+ * severe, that it can actually crash the system because of a NMI watchdog
+ * soft lockup, for example.
+ *
+ * If multiple CPUs are trying to access the HPET counter at the same time,
+ * we don't actually need to read the counter multiple times. Instead, the
+ * other CPUs can use the counter value read by the first CPU in the group.
+ *
+ * This special feature is only enabled on x86-64 systems. It is unlikely
+ * that 32-bit x86 systems will have enough CPUs to require this feature
+ * with its associated locking overhead. We also need 64-bit atomic read.
+ *
+ * The lock and the HPET value are stored together and can be read in a
+ * single atomic 64-bit read. It is explicitly assumed that arch_spinlock_t
+ * is 32 bits in size.
+ */
+union hpet_lock {
+	struct {
+		arch_spinlock_t lock;
+		u32 value;
+	};
+	u64 lockval;
+};
+
+static union hpet_lock hpet __cacheline_aligned = {
+	{ .lock = __ARCH_SPIN_LOCK_UNLOCKED, },
+};
+
+static u64 read_hpet(struct clocksource *cs)
+{
+	unsigned long flags;
+	union hpet_lock old, new;
+
+	BUILD_BUG_ON(sizeof(union hpet_lock) != 8);
+
+	/*
+	 * Read HPET directly if in NMI.
+	 */
+	if (in_nmi())
+		return (u64)hpet_readl(HPET_COUNTER);
+
+	/*
+	 * Read the current state of the lock and HPET value atomically.
+	 */
+	old.lockval = READ_ONCE(hpet.lockval);
+
+	if (arch_spin_is_locked(&old.lock))
+		goto contended;
+
+	local_irq_save(flags);
+	if (arch_spin_trylock(&hpet.lock)) {
+		new.value = hpet_readl(HPET_COUNTER);
+		/*
+		 * Use WRITE_ONCE() to prevent store tearing.
+		 */
+		WRITE_ONCE(hpet.value, new.value);
+		arch_spin_unlock(&hpet.lock);
+		local_irq_restore(flags);
+		return (u64)new.value;
+	}
+	local_irq_restore(flags);
+
+contended:
+	/*
+	 * Contended case
+	 * --------------
+	 * Wait until the HPET value change or the lock is free to indicate
+	 * its value is up-to-date.
+	 *
+	 * It is possible that old.value has already contained the latest
+	 * HPET value while the lock holder was in the process of releasing
+	 * the lock. Checking for lock state change will enable us to return
+	 * the value immediately instead of waiting for the next HPET reader
+	 * to come along.
+	 */
+	do {
+		cpu_relax();
+		new.lockval = READ_ONCE(hpet.lockval);
+	} while ((new.value == old.value) && arch_spin_is_locked(&new.lock));
+
+	return (u64)new.value;
+}
+#else
+/*
+ * For UP or 32-bit.
+ */
+static u64 read_hpet(struct clocksource *cs)
+{
+	return (u64)hpet_readl(HPET_COUNTER);
+}
+#endif
+
+static struct clocksource clocksource_hpet = {
+	.name		= "hpet",
+	.rating		= 250,
+	.read		= read_hpet,
+	.mask		= HPET_MASK,
+	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
+	.resume		= hpet_resume_counter,
+};
+
+/*
+ * AMD SB700 based systems with spread spectrum enabled use a SMM based
+ * HPET emulation to provide proper frequency setting.
+ *
+ * On such systems the SMM code is initialized with the first HPET register
+ * access and takes some time to complete. During this time the config
+ * register reads 0xffffffff. We check for max 1000 loops whether the
+ * config register reads a non-0xffffffff value to make sure that the
+ * HPET is up and running before we proceed any further.
+ *
+ * A counting loop is safe, as the HPET access takes thousands of CPU cycles.
+ *
+ * On non-SB700 based machines this check is only done once and has no
+ * side effects.
+ */
+static bool __init hpet_cfg_working(void)
+{
+	int i;
+
+	for (i = 0; i < 1000; i++) {
+		if (hpet_readl(HPET_CFG) != 0xFFFFFFFF)
+			return true;
+	}
+
+	pr_warn("Config register invalid. Disabling HPET\n");
+	return false;
+}
+
+static bool __init hpet_counting(void)
+{
+	u64 start, now, t1;
+
+	hpet_restart_counter();
+
+	t1 = hpet_readl(HPET_COUNTER);
+	start = rdtsc();
+
+	/*
+	 * We don't know the TSC frequency yet, but waiting for
+	 * 200000 TSC cycles is safe:
+	 * 4 GHz == 50us
+	 * 1 GHz == 200us
+	 */
+	do {
+		if (t1 != hpet_readl(HPET_COUNTER))
+			return true;
+		now = rdtsc();
+	} while ((now - start) < 200000UL);
+
+	pr_warn("Counter not counting. HPET disabled\n");
+	return false;
+}
+
+static bool __init mwait_pc10_supported(void)
+{
+	unsigned int eax, ebx, ecx, mwait_substates;
+
+	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
+		return false;
+
+	if (!cpu_feature_enabled(X86_FEATURE_MWAIT))
+		return false;
+
+	if (boot_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
+		return false;
+
+	cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &mwait_substates);
+
+	return (ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) &&
+	       (ecx & CPUID5_ECX_INTERRUPT_BREAK) &&
+	       (mwait_substates & (0xF << 28));
+}
+
+/*
+ * Check whether the system supports PC10. If so force disable HPET as that
+ * stops counting in PC10. This check is overbroad as it does not take any
+ * of the following into account:
+ *
+ *	- ACPI tables
+ *	- Enablement of intel_idle
+ *	- Command line arguments which limit intel_idle C-state support
+ *
+ * That's perfectly fine. HPET is a piece of hardware designed by committee
+ * and the only reasons why it is still in use on modern systems is the
+ * fact that it is impossible to reliably query TSC and CPU frequency via
+ * CPUID or firmware.
+ *
+ * If HPET is functional it is useful for calibrating TSC, but this can be
+ * done via PMTIMER as well which seems to be the last remaining timer on
+ * X86/INTEL platforms that has not been completely wreckaged by feature
+ * creep.
+ *
+ * In theory HPET support should be removed altogether, but there are older
+ * systems out there which depend on it because TSC and APIC timer are
+ * dysfunctional in deeper C-states.
+ *
+ * It's only 20 years now that hardware people have been asked to provide
+ * reliable and discoverable facilities which can be used for timekeeping
+ * and per CPU timer interrupts.
+ *
+ * The probability that this problem is going to be solved in the
+ * forseeable future is close to zero, so the kernel has to be cluttered
+ * with heuristics to keep up with the ever growing amount of hardware and
+ * firmware trainwrecks. Hopefully some day hardware people will understand
+ * that the approach of "This can be fixed in software" is not sustainable.
+ * Hope dies last...
+ */
+static bool __init hpet_is_pc10_damaged(void)
+{
+	unsigned long long pcfg;
+
+	/* Check whether PC10 substates are supported */
+	if (!mwait_pc10_supported())
+		return false;
+
+	/* Check whether PC10 is enabled in PKG C-state limit */
+	rdmsrl(MSR_PKG_CST_CONFIG_CONTROL, pcfg);
+	if ((pcfg & 0xF) < 8)
+		return false;
+
+	if (hpet_force_user) {
+		pr_warn("HPET force enabled via command line, but dysfunctional in PC10.\n");
+		return false;
+	}
+
+	pr_info("HPET dysfunctional in PC10. Force disabled.\n");
+	boot_hpet_disable = true;
+	return true;
+}
+
+/**
+ * hpet_enable - Try to setup the HPET timer. Returns 1 on success.
+ */
+int __init hpet_enable(void)
+{
+	u32 hpet_period, cfg, id, irq;
+	unsigned int i, channels;
+	struct hpet_channel *hc;
+	u64 freq;
+
+	if (!is_hpet_capable())
+		return 0;
+
+	if (hpet_is_pc10_damaged())
+		return 0;
+
+	hpet_set_mapping();
+	if (!hpet_virt_address)
+		return 0;
+
+	/* Validate that the config register is working */
+	if (!hpet_cfg_working())
+		goto out_nohpet;
+
+	/*
+	 * Read the period and check for a sane value:
+	 */
+	hpet_period = hpet_readl(HPET_PERIOD);
+	if (hpet_period < HPET_MIN_PERIOD || hpet_period > HPET_MAX_PERIOD)
+		goto out_nohpet;
+
+	/* The period is a femtoseconds value. Convert it to a frequency. */
+	freq = FSEC_PER_SEC;
+	do_div(freq, hpet_period);
+	hpet_freq = freq;
+
+	/*
+	 * Read the HPET ID register to retrieve the IRQ routing
+	 * information and the number of channels
+	 */
+	id = hpet_readl(HPET_ID);
+	hpet_print_config();
+
+	/* This is the HPET channel number which is zero based */
+	channels = ((id & HPET_ID_NUMBER) >> HPET_ID_NUMBER_SHIFT) + 1;
+
+	/*
+	 * The legacy routing mode needs at least two channels, tick timer
+	 * and the rtc emulation channel.
+	 */
+	if (IS_ENABLED(CONFIG_HPET_EMULATE_RTC) && channels < 2)
+		goto out_nohpet;
+
+	hc = kcalloc(channels, sizeof(*hc), GFP_KERNEL);
+	if (!hc) {
+		pr_warn("Disabling HPET.\n");
+		goto out_nohpet;
+	}
+	hpet_base.channels = hc;
+	hpet_base.nr_channels = channels;
+
+	/* Read, store and sanitize the global configuration */
+	cfg = hpet_readl(HPET_CFG);
+	hpet_base.boot_cfg = cfg;
+	cfg &= ~(HPET_CFG_ENABLE | HPET_CFG_LEGACY);
+	hpet_writel(cfg, HPET_CFG);
+	if (cfg)
+		pr_warn("Global config: Unknown bits %#x\n", cfg);
+
+	/* Read, store and sanitize the per channel configuration */
+	for (i = 0; i < channels; i++, hc++) {
+		hc->num = i;
+
+		cfg = hpet_readl(HPET_Tn_CFG(i));
+		hc->boot_cfg = cfg;
+		irq = (cfg & Tn_INT_ROUTE_CNF_MASK) >> Tn_INT_ROUTE_CNF_SHIFT;
+		hc->irq = irq;
+
+		cfg &= ~(HPET_TN_ENABLE | HPET_TN_LEVEL | HPET_TN_FSB);
+		hpet_writel(cfg, HPET_Tn_CFG(i));
+
+		cfg &= ~(HPET_TN_PERIODIC | HPET_TN_PERIODIC_CAP
+			 | HPET_TN_64BIT_CAP | HPET_TN_32BIT | HPET_TN_ROUTE
+			 | HPET_TN_FSB | HPET_TN_FSB_CAP);
+		if (cfg)
+			pr_warn("Channel #%u config: Unknown bits %#x\n", i, cfg);
+	}
+	hpet_print_config();
+
+	/*
+	 * Validate that the counter is counting. This needs to be done
+	 * after sanitizing the config registers to properly deal with
+	 * force enabled HPETs.
+	 */
+	if (!hpet_counting())
+		goto out_nohpet;
+
+	clocksource_register_hz(&clocksource_hpet, (u32)hpet_freq);
+
+	if (id & HPET_ID_LEGSUP) {
+		hpet_legacy_clockevent_register(&hpet_base.channels[0]);
+		hpet_base.channels[0].mode = HPET_MODE_LEGACY;
+		if (IS_ENABLED(CONFIG_HPET_EMULATE_RTC))
+			hpet_base.channels[1].mode = HPET_MODE_LEGACY;
+		return 1;
+	}
+	return 0;
+
+out_nohpet:
+	kfree(hpet_base.channels);
+	hpet_base.channels = NULL;
+	hpet_base.nr_channels = 0;
+	hpet_clear_mapping();
+	hpet_address = 0;
+	return 0;
+}
+
+/*
+ * The late initialization runs after the PCI quirks have been invoked
+ * which might have detected a system on which the HPET can be enforced.
+ *
+ * Also, the MSI machinery is not working yet when the HPET is initialized
+ * early.
+ *
+ * If the HPET is enabled, then:
+ *
+ *  1) Reserve one channel for /dev/hpet if CONFIG_HPET=y
+ *  2) Reserve up to num_possible_cpus() channels as per CPU clockevents
+ *  3) Setup /dev/hpet if CONFIG_HPET=y
+ *  4) Register hotplug callbacks when clockevents are available
+ */
+static __init int hpet_late_init(void)
+{
+	int ret;
+
+	if (!hpet_address) {
+		if (!force_hpet_address)
+			return -ENODEV;
+
+		hpet_address = force_hpet_address;
+		hpet_enable();
+	}
+
+	if (!hpet_virt_address)
+		return -ENODEV;
+
+	hpet_select_device_channel();
+	hpet_select_clockevents();
+	hpet_reserve_platform_timers();
+	hpet_print_config();
+
+	if (!hpet_base.nr_clockevents)
+		return 0;
+
+	ret = cpuhp_setup_state(CPUHP_AP_X86_HPET_ONLINE, "x86/hpet:online",
+				hpet_cpuhp_online, NULL);
+	if (ret)
+		return ret;
+	ret = cpuhp_setup_state(CPUHP_X86_HPET_DEAD, "x86/hpet:dead", NULL,
+				hpet_cpuhp_dead);
+	if (ret)
+		goto err_cpuhp;
+	return 0;
+
+err_cpuhp:
+	cpuhp_remove_state(CPUHP_AP_X86_HPET_ONLINE);
+	return ret;
+}
+fs_initcall(hpet_late_init);
+
+void hpet_disable(void)
+{
+	unsigned int i;
+	u32 cfg;
+
+	if (!is_hpet_capable() || !hpet_virt_address)
+		return;
+
+	/* Restore boot configuration with the enable bit cleared */
+	cfg = hpet_base.boot_cfg;
+	cfg &= ~HPET_CFG_ENABLE;
+	hpet_writel(cfg, HPET_CFG);
+
+	/* Restore the channel boot configuration */
+	for (i = 0; i < hpet_base.nr_channels; i++)
+		hpet_writel(hpet_base.channels[i].boot_cfg, HPET_Tn_CFG(i));
+
+	/* If the HPET was enabled at boot time, reenable it */
+	if (hpet_base.boot_cfg & HPET_CFG_ENABLE)
+		hpet_writel(hpet_base.boot_cfg, HPET_CFG);
+}
+
+#ifdef CONFIG_HPET_EMULATE_RTC
+
+/*
+ * HPET in LegacyReplacement mode eats up the RTC interrupt line. When HPET
+ * is enabled, we support RTC interrupt functionality in software.
+ *
+ * RTC has 3 kinds of interrupts:
+ *
+ *  1) Update Interrupt - generate an interrupt, every second, when the
+ *     RTC clock is updated
+ *  2) Alarm Interrupt - generate an interrupt at a specific time of day
+ *  3) Periodic Interrupt - generate periodic interrupt, with frequencies
+ *     2Hz-8192Hz (2Hz-64Hz for non-root user) (all frequencies in powers of 2)
+ *
+ * (1) and (2) above are implemented using polling at a frequency of 64 Hz:
+ * DEFAULT_RTC_INT_FREQ.
+ *
+ * The exact frequency is a tradeoff between accuracy and interrupt overhead.
+ *
+ * For (3), we use interrupts at 64 Hz, or the user specified periodic frequency,
+ * if it's higher.
+ */
+#include <linux/mc146818rtc.h>
+#include <linux/rtc.h>
+
+#define DEFAULT_RTC_INT_FREQ	64
+#define DEFAULT_RTC_SHIFT	6
+#define RTC_NUM_INTS		1
+
+static unsigned long hpet_rtc_flags;
+static int hpet_prev_update_sec;
+static struct rtc_time hpet_alarm_time;
+static unsigned long hpet_pie_count;
+static u32 hpet_t1_cmp;
+static u32 hpet_default_delta;
+static u32 hpet_pie_delta;
+static unsigned long hpet_pie_limit;
+
+static rtc_irq_handler irq_handler;
+
+/*
+ * Check that the HPET counter c1 is ahead of c2
+ */
+static inline int hpet_cnt_ahead(u32 c1, u32 c2)
+{
+	return (s32)(c2 - c1) < 0;
+}
+
+/*
+ * Registers a IRQ handler.
+ */
+int hpet_register_irq_handler(rtc_irq_handler handler)
+{
+	if (!is_hpet_enabled())
+		return -ENODEV;
+	if (irq_handler)
+		return -EBUSY;
+
+	irq_handler = handler;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(hpet_register_irq_handler);
+
+/*
+ * Deregisters the IRQ handler registered with hpet_register_irq_handler()
+ * and does cleanup.
+ */
+void hpet_unregister_irq_handler(rtc_irq_handler handler)
+{
+	if (!is_hpet_enabled())
+		return;
+
+	irq_handler = NULL;
+	hpet_rtc_flags = 0;
+}
+EXPORT_SYMBOL_GPL(hpet_unregister_irq_handler);
+
+/*
+ * Channel 1 for RTC emulation. We use one shot mode, as periodic mode
+ * is not supported by all HPET implementations for channel 1.
+ *
+ * hpet_rtc_timer_init() is called when the rtc is initialized.
+ */
+int hpet_rtc_timer_init(void)
+{
+	unsigned int cfg, cnt, delta;
+	unsigned long flags;
+
+	if (!is_hpet_enabled())
+		return 0;
+
+	if (!hpet_default_delta) {
+		struct clock_event_device *evt = &hpet_base.channels[0].evt;
+		uint64_t clc;
+
+		clc = (uint64_t) evt->mult * NSEC_PER_SEC;
+		clc >>= evt->shift + DEFAULT_RTC_SHIFT;
+		hpet_default_delta = clc;
+	}
+
+	if (!(hpet_rtc_flags & RTC_PIE) || hpet_pie_limit)
+		delta = hpet_default_delta;
+	else
+		delta = hpet_pie_delta;
+
+	local_irq_save(flags);
+
+	cnt = delta + hpet_readl(HPET_COUNTER);
+	hpet_writel(cnt, HPET_T1_CMP);
+	hpet_t1_cmp = cnt;
+
+	cfg = hpet_readl(HPET_T1_CFG);
+	cfg &= ~HPET_TN_PERIODIC;
+	cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
+	hpet_writel(cfg, HPET_T1_CFG);
+
+	local_irq_restore(flags);
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(hpet_rtc_timer_init);
+
+static void hpet_disable_rtc_channel(void)
+{
+	u32 cfg = hpet_readl(HPET_T1_CFG);
+
+	cfg &= ~HPET_TN_ENABLE;
+	hpet_writel(cfg, HPET_T1_CFG);
+}
+
+/*
+ * The functions below are called from rtc driver.
+ * Return 0 if HPET is not being used.
+ * Otherwise do the necessary changes and return 1.
+ */
+int hpet_mask_rtc_irq_bit(unsigned long bit_mask)
+{
+	if (!is_hpet_enabled())
+		return 0;
+
+	hpet_rtc_flags &= ~bit_mask;
+	if (unlikely(!hpet_rtc_flags))
+		hpet_disable_rtc_channel();
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(hpet_mask_rtc_irq_bit);
+
+int hpet_set_rtc_irq_bit(unsigned long bit_mask)
+{
+	unsigned long oldbits = hpet_rtc_flags;
+
+	if (!is_hpet_enabled())
+		return 0;
+
+	hpet_rtc_flags |= bit_mask;
+
+	if ((bit_mask & RTC_UIE) && !(oldbits & RTC_UIE))
+		hpet_prev_update_sec = -1;
+
+	if (!oldbits)
+		hpet_rtc_timer_init();
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(hpet_set_rtc_irq_bit);
+
+int hpet_set_alarm_time(unsigned char hrs, unsigned char min, unsigned char sec)
+{
+	if (!is_hpet_enabled())
+		return 0;
+
+	hpet_alarm_time.tm_hour = hrs;
+	hpet_alarm_time.tm_min = min;
+	hpet_alarm_time.tm_sec = sec;
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(hpet_set_alarm_time);
+
+int hpet_set_periodic_freq(unsigned long freq)
+{
+	uint64_t clc;
+
+	if (!is_hpet_enabled())
+		return 0;
+
+	if (freq <= DEFAULT_RTC_INT_FREQ) {
+		hpet_pie_limit = DEFAULT_RTC_INT_FREQ / freq;
+	} else {
+		struct clock_event_device *evt = &hpet_base.channels[0].evt;
+
+		clc = (uint64_t) evt->mult * NSEC_PER_SEC;
+		do_div(clc, freq);
+		clc >>= evt->shift;
+		hpet_pie_delta = clc;
+		hpet_pie_limit = 0;
+	}
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(hpet_set_periodic_freq);
+
+int hpet_rtc_dropped_irq(void)
+{
+	return is_hpet_enabled();
+}
+EXPORT_SYMBOL_GPL(hpet_rtc_dropped_irq);
+
+static void hpet_rtc_timer_reinit(void)
+{
+	unsigned int delta;
+	int lost_ints = -1;
+
+	if (unlikely(!hpet_rtc_flags))
+		hpet_disable_rtc_channel();
+
+	if (!(hpet_rtc_flags & RTC_PIE) || hpet_pie_limit)
+		delta = hpet_default_delta;
+	else
+		delta = hpet_pie_delta;
+
+	/*
+	 * Increment the comparator value until we are ahead of the
+	 * current count.
+	 */
+	do {
+		hpet_t1_cmp += delta;
+		hpet_writel(hpet_t1_cmp, HPET_T1_CMP);
+		lost_ints++;
+	} while (!hpet_cnt_ahead(hpet_t1_cmp, hpet_readl(HPET_COUNTER)));
+
+	if (lost_ints) {
+		if (hpet_rtc_flags & RTC_PIE)
+			hpet_pie_count += lost_ints;
+		if (printk_ratelimit())
+			pr_warn("Lost %d RTC interrupts\n", lost_ints);
+	}
+}
+
+irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id)
+{
+	struct rtc_time curr_time;
+	unsigned long rtc_int_flag = 0;
+
+	hpet_rtc_timer_reinit();
+	memset(&curr_time, 0, sizeof(struct rtc_time));
+
+	if (hpet_rtc_flags & (RTC_UIE | RTC_AIE)) {
+		if (unlikely(mc146818_get_time(&curr_time) < 0)) {
+			pr_err_ratelimited("unable to read current time from RTC\n");
+			return IRQ_HANDLED;
+		}
+	}
+
+	if (hpet_rtc_flags & RTC_UIE &&
+	    curr_time.tm_sec != hpet_prev_update_sec) {
+		if (hpet_prev_update_sec >= 0)
+			rtc_int_flag = RTC_UF;
+		hpet_prev_update_sec = curr_time.tm_sec;
+	}
+
+	if (hpet_rtc_flags & RTC_PIE && ++hpet_pie_count >= hpet_pie_limit) {
+		rtc_int_flag |= RTC_PF;
+		hpet_pie_count = 0;
+	}
+
+	if (hpet_rtc_flags & RTC_AIE &&
+	    (curr_time.tm_sec == hpet_alarm_time.tm_sec) &&
+	    (curr_time.tm_min == hpet_alarm_time.tm_min) &&
+	    (curr_time.tm_hour == hpet_alarm_time.tm_hour))
+		rtc_int_flag |= RTC_AF;
+
+	if (rtc_int_flag) {
+		rtc_int_flag |= (RTC_IRQF | (RTC_NUM_INTS << 8));
+		if (irq_handler)
+			irq_handler(rtc_int_flag, dev_id);
+	}
+	return IRQ_HANDLED;
+}
+EXPORT_SYMBOL_GPL(hpet_rtc_interrupt);
+#endif