// 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/irq_remapping.h>
#include <asm/hpet.h>
#include <asm/time.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_GENERIC_MSI_IRQ
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_GENERIC_MSI_IRQ
static 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));
}

static 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));
}

static 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 void hpet_msi_write_msg(struct irq_data *data, struct msi_msg *msg)
{
        hpet_msi_write(irq_data_get_irq_handler_data(data), msg);
}

static struct irq_chip hpet_msi_controller __ro_after_init = {
        .name = "HPET-MSI",
        .irq_unmask = hpet_msi_unmask,
        .irq_mask = hpet_msi_mask,
        .irq_ack = irq_chip_ack_parent,
        .irq_set_affinity = msi_domain_set_affinity,
        .irq_retrigger = irq_chip_retrigger_hierarchy,
        .irq_write_msi_msg = hpet_msi_write_msg,
        .flags = IRQCHIP_SKIP_SET_WAKE | IRQCHIP_AFFINITY_PRE_STARTUP,
};

static int hpet_msi_init(struct irq_domain *domain,
                         struct msi_domain_info *info, unsigned int virq,
                         irq_hw_number_t hwirq, msi_alloc_info_t *arg)
{
        irq_set_status_flags(virq, IRQ_MOVE_PCNTXT);
        irq_domain_set_info(domain, virq, arg->hwirq, info->chip, NULL,
                            handle_edge_irq, arg->data, "edge");

        return 0;
}

static void hpet_msi_free(struct irq_domain *domain,
                          struct msi_domain_info *info, unsigned int virq)
{
        irq_clear_status_flags(virq, IRQ_MOVE_PCNTXT);
}

static struct msi_domain_ops hpet_msi_domain_ops = {
        .msi_init       = hpet_msi_init,
        .msi_free       = hpet_msi_free,
};

static struct msi_domain_info hpet_msi_domain_info = {
        .ops            = &hpet_msi_domain_ops,
        .chip           = &hpet_msi_controller,
        .flags          = MSI_FLAG_USE_DEF_DOM_OPS,
};

static struct irq_domain *hpet_create_irq_domain(int hpet_id)
{
        struct msi_domain_info *domain_info;
        struct irq_domain *parent, *d;
        struct fwnode_handle *fn;
        struct irq_fwspec fwspec;

        if (x86_vector_domain == NULL)
                return NULL;

        domain_info = kzalloc(sizeof(*domain_info), GFP_KERNEL);
        if (!domain_info)
                return NULL;

        *domain_info = hpet_msi_domain_info;
        domain_info->data = (void *)(long)hpet_id;

        fn = irq_domain_alloc_named_id_fwnode(hpet_msi_controller.name,
                                              hpet_id);
        if (!fn) {
                kfree(domain_info);
                return NULL;
        }

        fwspec.fwnode = fn;
        fwspec.param_count = 1;
        fwspec.param[0] = hpet_id;

        parent = irq_find_matching_fwspec(&fwspec, DOMAIN_BUS_ANY);
        if (!parent) {
                irq_domain_free_fwnode(fn);
                kfree(domain_info);
                return NULL;
        }
        if (parent != x86_vector_domain)
                hpet_msi_controller.name = "IR-HPET-MSI";

        d = msi_create_irq_domain(fn, domain_info, parent);
        if (!d) {
                irq_domain_free_fwnode(fn);
                kfree(domain_info);
        }
        return d;
}

static inline int hpet_dev_id(struct irq_domain *domain)
{
        struct msi_domain_info *info = msi_get_domain_info(domain);

        return (int)(long)info->data;
}

static int hpet_assign_irq(struct irq_domain *domain, struct hpet_channel *hc,
                           int dev_num)
{
        struct irq_alloc_info info;

        init_irq_alloc_info(&info, NULL);
        info.type = X86_IRQ_ALLOC_TYPE_HPET;
        info.data = hc;
        info.devid = hpet_dev_id(domain);
        info.hwirq = dev_num;

        return irq_domain_alloc_irqs(domain, 1, NUMA_NO_NODE, &info);
}

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;
}

/**
 * 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;

        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))
                mc146818_get_time(&curr_time);

        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