linux/include/clocksource/hyperv_timer.h
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   1/* SPDX-License-Identifier: GPL-2.0 */
   2
   3/*
   4 * Definitions for the clocksource provided by the Hyper-V
   5 * hypervisor to guest VMs, as described in the Hyper-V Top
   6 * Level Functional Spec (TLFS).
   7 *
   8 * Copyright (C) 2019, Microsoft, Inc.
   9 *
  10 * Author:  Michael Kelley <mikelley@microsoft.com>
  11 */
  12
  13#ifndef __CLKSOURCE_HYPERV_TIMER_H
  14#define __CLKSOURCE_HYPERV_TIMER_H
  15
  16#include <linux/clocksource.h>
  17#include <linux/math64.h>
  18#include <asm/mshyperv.h>
  19
  20#define HV_MAX_MAX_DELTA_TICKS 0xffffffff
  21#define HV_MIN_DELTA_TICKS 1
  22
  23/* Routines called by the VMbus driver */
  24extern int hv_stimer_alloc(int sint);
  25extern void hv_stimer_free(void);
  26extern void hv_stimer_init(unsigned int cpu);
  27extern void hv_stimer_cleanup(unsigned int cpu);
  28extern void hv_stimer_global_cleanup(void);
  29extern void hv_stimer0_isr(void);
  30
  31#ifdef CONFIG_HYPERV_TIMER
  32extern struct clocksource *hyperv_cs;
  33extern void hv_init_clocksource(void);
  34
  35extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
  36
  37static inline notrace u64
  38hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
  39{
  40        u64 scale, offset;
  41        u32 sequence;
  42
  43        /*
  44         * The protocol for reading Hyper-V TSC page is specified in Hypervisor
  45         * Top-Level Functional Specification ver. 3.0 and above. To get the
  46         * reference time we must do the following:
  47         * - READ ReferenceTscSequence
  48         *   A special '0' value indicates the time source is unreliable and we
  49         *   need to use something else. The currently published specification
  50         *   versions (up to 4.0b) contain a mistake and wrongly claim '-1'
  51         *   instead of '0' as the special value, see commit c35b82ef0294.
  52         * - ReferenceTime =
  53         *        ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
  54         * - READ ReferenceTscSequence again. In case its value has changed
  55         *   since our first reading we need to discard ReferenceTime and repeat
  56         *   the whole sequence as the hypervisor was updating the page in
  57         *   between.
  58         */
  59        do {
  60                sequence = READ_ONCE(tsc_pg->tsc_sequence);
  61                if (!sequence)
  62                        return U64_MAX;
  63                /*
  64                 * Make sure we read sequence before we read other values from
  65                 * TSC page.
  66                 */
  67                smp_rmb();
  68
  69                scale = READ_ONCE(tsc_pg->tsc_scale);
  70                offset = READ_ONCE(tsc_pg->tsc_offset);
  71                *cur_tsc = hv_get_raw_timer();
  72
  73                /*
  74                 * Make sure we read sequence after we read all other values
  75                 * from TSC page.
  76                 */
  77                smp_rmb();
  78
  79        } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
  80
  81        return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
  82}
  83
  84static inline notrace u64
  85hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
  86{
  87        u64 cur_tsc;
  88
  89        return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
  90}
  91
  92#else /* CONFIG_HYPERV_TIMER */
  93static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
  94{
  95        return NULL;
  96}
  97
  98static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
  99                                       u64 *cur_tsc)
 100{
 101        return U64_MAX;
 102}
 103#endif /* CONFIG_HYPERV_TIMER */
 104
 105#endif
 106