// SPDX-License-Identifier: GPL-2.0

/*
 * Clocksource driver for the synthetic counter and timers
 * provided by the Hyper-V hypervisor to guest VMs, as described
 * in the Hyper-V Top Level Functional Spec (TLFS). This driver
 * is instruction set architecture independent.
 *
 * Copyright (C) 2019, Microsoft, Inc.
 *
 * Author:  Michael Kelley <mikelley@microsoft.com>
 */

#include <linux/percpu.h>
#include <linux/cpumask.h>
#include <linux/clockchips.h>
#include <linux/clocksource.h>
#include <linux/sched_clock.h>
#include <linux/mm.h>
#include <linux/cpuhotplug.h>
#include <clocksource/hyperv_timer.h>
#include <asm/hyperv-tlfs.h>
#include <asm/mshyperv.h>

static struct clock_event_device __percpu *hv_clock_event;
static u64 hv_sched_clock_offset __ro_after_init;

/*
 * If false, we're using the old mechanism for stimer0 interrupts
 * where it sends a VMbus message when it expires. The old
 * mechanism is used when running on older versions of Hyper-V
 * that don't support Direct Mode. While Hyper-V provides
 * four stimer's per CPU, Linux uses only stimer0.
 *
 * Because Direct Mode does not require processing a VMbus
 * message, stimer interrupts can be enabled earlier in the
 * process of booting a CPU, and consistent with when timer
 * interrupts are enabled for other clocksource drivers.
 * However, for legacy versions of Hyper-V when Direct Mode
 * is not enabled, setting up stimer interrupts must be
 * delayed until VMbus is initialized and can process the
 * interrupt message.
 */
static bool direct_mode_enabled;

static int stimer0_irq;
static int stimer0_vector;
static int stimer0_message_sint;

/*
 * ISR for when stimer0 is operating in Direct Mode.  Direct Mode
 * does not use VMbus or any VMbus messages, so process here and not
 * in the VMbus driver code.
 */
void hv_stimer0_isr(void)
{
        struct clock_event_device *ce;

        ce = this_cpu_ptr(hv_clock_event);
        ce->event_handler(ce);
}
EXPORT_SYMBOL_GPL(hv_stimer0_isr);

static int hv_ce_set_next_event(unsigned long delta,
                                struct clock_event_device *evt)
{
        u64 current_tick;

        current_tick = hv_read_reference_counter();
        current_tick += delta;
        hv_init_timer(0, current_tick);
        return 0;
}

static int hv_ce_shutdown(struct clock_event_device *evt)
{
        hv_init_timer(0, 0);
        hv_init_timer_config(0, 0);
        if (direct_mode_enabled)
                hv_disable_stimer0_percpu_irq(stimer0_irq);

        return 0;
}

static int hv_ce_set_oneshot(struct clock_event_device *evt)
{
        union hv_stimer_config timer_cfg;

        timer_cfg.as_uint64 = 0;
        timer_cfg.enable = 1;
        timer_cfg.auto_enable = 1;
        if (direct_mode_enabled) {
                /*
                 * When it expires, the timer will directly interrupt
                 * on the specified hardware vector/IRQ.
                 */
                timer_cfg.direct_mode = 1;
                timer_cfg.apic_vector = stimer0_vector;
                hv_enable_stimer0_percpu_irq(stimer0_irq);
        } else {
                /*
                 * When it expires, the timer will generate a VMbus message,
                 * to be handled by the normal VMbus interrupt handler.
                 */
                timer_cfg.direct_mode = 0;
                timer_cfg.sintx = stimer0_message_sint;
        }
        hv_init_timer_config(0, timer_cfg.as_uint64);
        return 0;
}

/*
 * hv_stimer_init - Per-cpu initialization of the clockevent
 */
static int hv_stimer_init(unsigned int cpu)
{
        struct clock_event_device *ce;

        if (!hv_clock_event)
                return 0;

        ce = per_cpu_ptr(hv_clock_event, cpu);
        ce->name = "Hyper-V clockevent";
        ce->features = CLOCK_EVT_FEAT_ONESHOT;
        ce->cpumask = cpumask_of(cpu);
        ce->rating = 1000;
        ce->set_state_shutdown = hv_ce_shutdown;
        ce->set_state_oneshot = hv_ce_set_oneshot;
        ce->set_next_event = hv_ce_set_next_event;

        clockevents_config_and_register(ce,
                                        HV_CLOCK_HZ,
                                        HV_MIN_DELTA_TICKS,
                                        HV_MAX_MAX_DELTA_TICKS);
        return 0;
}

/*
 * hv_stimer_cleanup - Per-cpu cleanup of the clockevent
 */
int hv_stimer_cleanup(unsigned int cpu)
{
        struct clock_event_device *ce;

        if (!hv_clock_event)
                return 0;

        /*
         * In the legacy case where Direct Mode is not enabled
         * (which can only be on x86/64), stimer cleanup happens
         * relatively early in the CPU offlining process. We
         * must unbind the stimer-based clockevent device so
         * that the LAPIC timer can take over until clockevents
         * are no longer needed in the offlining process. Note
         * that clockevents_unbind_device() eventually calls
         * hv_ce_shutdown().
         *
         * The unbind should not be done when Direct Mode is
         * enabled because we may be on an architecture where
         * there are no other clockevent devices to fallback to.
         */
        ce = per_cpu_ptr(hv_clock_event, cpu);
        if (direct_mode_enabled)
                hv_ce_shutdown(ce);
        else
                clockevents_unbind_device(ce, cpu);

        return 0;
}
EXPORT_SYMBOL_GPL(hv_stimer_cleanup);

/* hv_stimer_alloc - Global initialization of the clockevent and stimer0 */
int hv_stimer_alloc(void)
{
        int ret = 0;

        /*
         * Synthetic timers are always available except on old versions of
         * Hyper-V on x86.  In that case, return as error as Linux will use a
         * clockevent based on emulated LAPIC timer hardware.
         */
        if (!(ms_hyperv.features & HV_MSR_SYNTIMER_AVAILABLE))
                return -EINVAL;

        hv_clock_event = alloc_percpu(struct clock_event_device);
        if (!hv_clock_event)
                return -ENOMEM;

        direct_mode_enabled = ms_hyperv.misc_features &
                        HV_STIMER_DIRECT_MODE_AVAILABLE;
        if (direct_mode_enabled) {
                ret = hv_setup_stimer0_irq(&stimer0_irq, &stimer0_vector,
                                hv_stimer0_isr);
                if (ret)
                        goto free_percpu;

                /*
                 * Since we are in Direct Mode, stimer initialization
                 * can be done now with a CPUHP value in the same range
                 * as other clockevent devices.
                 */
                ret = cpuhp_setup_state(CPUHP_AP_HYPERV_TIMER_STARTING,
                                "clockevents/hyperv/stimer:starting",
                                hv_stimer_init, hv_stimer_cleanup);
                if (ret < 0)
                        goto free_stimer0_irq;
        }
        return ret;

free_stimer0_irq:
        hv_remove_stimer0_irq(stimer0_irq);
        stimer0_irq = 0;
free_percpu:
        free_percpu(hv_clock_event);
        hv_clock_event = NULL;
        return ret;
}
EXPORT_SYMBOL_GPL(hv_stimer_alloc);

/*
 * hv_stimer_legacy_init -- Called from the VMbus driver to handle
 * the case when Direct Mode is not enabled, and the stimer
 * must be initialized late in the CPU onlining process.
 *
 */
void hv_stimer_legacy_init(unsigned int cpu, int sint)
{
        if (direct_mode_enabled)
                return;

        /*
         * This function gets called by each vCPU, so setting the
         * global stimer_message_sint value each time is conceptually
         * not ideal, but the value passed in is always the same and
         * it avoids introducing yet another interface into this
         * clocksource driver just to set the sint in the legacy case.
         */
        stimer0_message_sint = sint;
        (void)hv_stimer_init(cpu);
}
EXPORT_SYMBOL_GPL(hv_stimer_legacy_init);

/*
 * hv_stimer_legacy_cleanup -- Called from the VMbus driver to
 * handle the case when Direct Mode is not enabled, and the
 * stimer must be cleaned up early in the CPU offlining
 * process.
 */
void hv_stimer_legacy_cleanup(unsigned int cpu)
{
        if (direct_mode_enabled)
                return;
        (void)hv_stimer_cleanup(cpu);
}
EXPORT_SYMBOL_GPL(hv_stimer_legacy_cleanup);


/* hv_stimer_free - Free global resources allocated by hv_stimer_alloc() */
void hv_stimer_free(void)
{
        if (!hv_clock_event)
                return;

        if (direct_mode_enabled) {
                cpuhp_remove_state(CPUHP_AP_HYPERV_TIMER_STARTING);
                hv_remove_stimer0_irq(stimer0_irq);
                stimer0_irq = 0;
        }
        free_percpu(hv_clock_event);
        hv_clock_event = NULL;
}
EXPORT_SYMBOL_GPL(hv_stimer_free);

/*
 * Do a global cleanup of clockevents for the cases of kexec and
 * vmbus exit
 */
void hv_stimer_global_cleanup(void)
{
        int     cpu;

        /*
         * hv_stime_legacy_cleanup() will stop the stimer if Direct
         * Mode is not enabled, and fallback to the LAPIC timer.
         */
        for_each_present_cpu(cpu) {
                hv_stimer_legacy_cleanup(cpu);
        }

        /*
         * If Direct Mode is enabled, the cpuhp teardown callback
         * (hv_stimer_cleanup) will be run on all CPUs to stop the
         * stimers.
         */
        hv_stimer_free();
}
EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup);

/*
 * Code and definitions for the Hyper-V clocksources.  Two
 * clocksources are defined: one that reads the Hyper-V defined MSR, and
 * the other that uses the TSC reference page feature as defined in the
 * TLFS.  The MSR version is for compatibility with old versions of
 * Hyper-V and 32-bit x86.  The TSC reference page version is preferred.
 *
 * The Hyper-V clocksource ratings of 250 are chosen to be below the
 * TSC clocksource rating of 300.  In configurations where Hyper-V offers
 * an InvariantTSC, the TSC is not marked "unstable", so the TSC clocksource
 * is available and preferred.  With the higher rating, it will be the
 * default.  On older hardware and Hyper-V versions, the TSC is marked
 * "unstable", so no TSC clocksource is created and the selected Hyper-V
 * clocksource will be the default.
 */

u64 (*hv_read_reference_counter)(void);
EXPORT_SYMBOL_GPL(hv_read_reference_counter);

static union {
        struct ms_hyperv_tsc_page page;
        u8 reserved[PAGE_SIZE];
} tsc_pg __aligned(PAGE_SIZE);

struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
{
        return &tsc_pg.page;
}
EXPORT_SYMBOL_GPL(hv_get_tsc_page);

static u64 notrace read_hv_clock_tsc(void)
{
        u64 current_tick = hv_read_tsc_page(hv_get_tsc_page());

        if (current_tick == U64_MAX)
                hv_get_time_ref_count(current_tick);

        return current_tick;
}

static u64 notrace read_hv_clock_tsc_cs(struct clocksource *arg)
{
        return read_hv_clock_tsc();
}

static u64 read_hv_sched_clock_tsc(void)
{
        return (read_hv_clock_tsc() - hv_sched_clock_offset) *
                (NSEC_PER_SEC / HV_CLOCK_HZ);
}

static void suspend_hv_clock_tsc(struct clocksource *arg)
{
        u64 tsc_msr;

        /* Disable the TSC page */
        hv_get_reference_tsc(tsc_msr);
        tsc_msr &= ~BIT_ULL(0);
        hv_set_reference_tsc(tsc_msr);
}


static void resume_hv_clock_tsc(struct clocksource *arg)
{
        phys_addr_t phys_addr = virt_to_phys(&tsc_pg);
        u64 tsc_msr;

        /* Re-enable the TSC page */
        hv_get_reference_tsc(tsc_msr);
        tsc_msr &= GENMASK_ULL(11, 0);
        tsc_msr |= BIT_ULL(0) | (u64)phys_addr;
        hv_set_reference_tsc(tsc_msr);
}

static int hv_cs_enable(struct clocksource *cs)
{
        hv_enable_vdso_clocksource();
        return 0;
}

static struct clocksource hyperv_cs_tsc = {
        .name   = "hyperv_clocksource_tsc_page",
        .rating = 250,
        .read   = read_hv_clock_tsc_cs,
        .mask   = CLOCKSOURCE_MASK(64),
        .flags  = CLOCK_SOURCE_IS_CONTINUOUS,
        .suspend= suspend_hv_clock_tsc,
        .resume = resume_hv_clock_tsc,
        .enable = hv_cs_enable,
};

static u64 notrace read_hv_clock_msr(void)
{
        u64 current_tick;
        /*
         * Read the partition counter to get the current tick count. This count
         * is set to 0 when the partition is created and is incremented in
         * 100 nanosecond units.
         */
        hv_get_time_ref_count(current_tick);
        return current_tick;
}

static u64 notrace read_hv_clock_msr_cs(struct clocksource *arg)
{
        return read_hv_clock_msr();
}

static u64 read_hv_sched_clock_msr(void)
{
        return (read_hv_clock_msr() - hv_sched_clock_offset) *
                (NSEC_PER_SEC / HV_CLOCK_HZ);
}

static struct clocksource hyperv_cs_msr = {
        .name   = "hyperv_clocksource_msr",
        .rating = 250,
        .read   = read_hv_clock_msr_cs,
        .mask   = CLOCKSOURCE_MASK(64),
        .flags  = CLOCK_SOURCE_IS_CONTINUOUS,
};

static bool __init hv_init_tsc_clocksource(void)
{
        u64             tsc_msr;
        phys_addr_t     phys_addr;

        if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
                return false;

        hv_read_reference_counter = read_hv_clock_tsc;
        phys_addr = virt_to_phys(hv_get_tsc_page());

        /*
         * The Hyper-V TLFS specifies to preserve the value of reserved
         * bits in registers. So read the existing value, preserve the
         * low order 12 bits, and add in the guest physical address
         * (which already has at least the low 12 bits set to zero since
         * it is page aligned). Also set the "enable" bit, which is bit 0.
         */
        hv_get_reference_tsc(tsc_msr);
        tsc_msr &= GENMASK_ULL(11, 0);
        tsc_msr = tsc_msr | 0x1 | (u64)phys_addr;
        hv_set_reference_tsc(tsc_msr);

        hv_set_clocksource_vdso(hyperv_cs_tsc);
        clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);

        hv_sched_clock_offset = hv_read_reference_counter();
        hv_setup_sched_clock(read_hv_sched_clock_tsc);

        return true;
}

void __init hv_init_clocksource(void)
{
        /*
         * Try to set up the TSC page clocksource. If it succeeds, we're
         * done. Otherwise, set up the MSR clocksoruce.  At least one of
         * these will always be available except on very old versions of
         * Hyper-V on x86.  In that case we won't have a Hyper-V
         * clocksource, but Linux will still run with a clocksource based
         * on the emulated PIT or LAPIC timer.
         */
        if (hv_init_tsc_clocksource())
                return;

        if (!(ms_hyperv.features & HV_MSR_TIME_REF_COUNT_AVAILABLE))
                return;

        hv_read_reference_counter = read_hv_clock_msr;
        clocksource_register_hz(&hyperv_cs_msr, NSEC_PER_SEC/100);

        hv_sched_clock_offset = hv_read_reference_counter();
        hv_setup_sched_clock(read_hv_sched_clock_msr);
}
EXPORT_SYMBOL_GPL(hv_init_clocksource);