/* SPDX-License-Identifier: GPL-2.0 */

/*
 * Definitions for the clocksource provided by the Hyper-V
 * hypervisor to guest VMs, as described in the Hyper-V Top
 * Level Functional Spec (TLFS).
 *
 * Copyright (C) 2019, Microsoft, Inc.
 *
 * Author:  Michael Kelley <[email protected]>
 */

#ifndef __CLKSOURCE_HYPERV_TIMER_H
#define __CLKSOURCE_HYPERV_TIMER_H

#include <linux/clocksource.h>
#include <linux/math64.h>
#include <asm/hyperv-tlfs.h>

#define HV_MAX_MAX_DELTA_TICKS 0xffffffff
#define HV_MIN_DELTA_TICKS 1

#ifdef CONFIG_HYPERV_TIMER

#include <asm/hyperv_timer.h>

/* Routines called by the VMbus driver */
extern int hv_stimer_alloc(bool have_percpu_irqs);
extern int hv_stimer_cleanup(unsigned int cpu);
extern void hv_stimer_legacy_init(unsigned int cpu, int sint);
extern void hv_stimer_legacy_cleanup(unsigned int cpu);
extern void hv_stimer_global_cleanup(void);
extern void hv_stimer0_isr(void);

extern void hv_init_clocksource(void);
extern void hv_remap_tsc_clocksource(void);

extern unsigned long hv_get_tsc_pfn(void);
extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);

static __always_inline bool
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
             u64 *cur_tsc, u64 *time)
{
    u64 scale, offset;
    u32 sequence;

    /*
     * The protocol for reading Hyper-V TSC page is specified in Hypervisor
     * Top-Level Functional Specification ver. 3.0 and above. To get the
     * reference time we must do the following:
     * - READ ReferenceTscSequence
     *   A special '0' value indicates the time source is unreliable and we
     *   need to use something else. The currently published specification
     *   versions (up to 4.0b) contain a mistake and wrongly claim '-1'
     *   instead of '0' as the special value, see commit c35b82ef0294.
     * - ReferenceTime =
     *        ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
     * - READ ReferenceTscSequence again. In case its value has changed
     *   since our first reading we need to discard ReferenceTime and repeat
     *   the whole sequence as the hypervisor was updating the page in
     *   between.
     */
    do {
        sequence = READ_ONCE(tsc_pg->tsc_sequence);
        if (!sequence)
            return false;
        /*
         * Make sure we read sequence before we read other values from
         * TSC page.
         */
        smp_rmb();

        scale = READ_ONCE(tsc_pg->tsc_scale);
        offset = READ_ONCE(tsc_pg->tsc_offset);
        *cur_tsc = hv_get_raw_timer();

        /*
         * Make sure we read sequence after we read all other values
         * from TSC page.
         */
        smp_rmb();

    } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);

    *time = mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
    return true;
}

#else /* CONFIG_HYPERV_TIMER */
static inline unsigned long hv_get_tsc_pfn(void)
{
    return 0;
}

static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
{
    return NULL;
}

static __always_inline bool
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc, u64 *time)
{
    return false;
}

static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
static inline void hv_stimer_global_cleanup(void) {}
static inline void hv_stimer0_isr(void) {}

#endif /* CONFIG_HYPERV_TIMER */

#endif