include/clocksource/hyperv_timer.h

   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/hyperv-tlfs.h>
  19
  20 #define HV_MAX_MAX_DELTA_TICKS 0xffffffff
  21 #define HV_MIN_DELTA_TICKS 1
  22
  23 #ifdef CONFIG_HYPERV_TIMER
  24
  25 #include <asm/hyperv_timer.h>
  26
  27 /* Routines called by the VMbus driver */
  28 extern int hv_stimer_alloc(bool have_percpu_irqs);
  29 extern int hv_stimer_cleanup(unsigned int cpu);
  30 extern void hv_stimer_legacy_init(unsigned int cpu, int sint);
  31 extern void hv_stimer_legacy_cleanup(unsigned int cpu);
  32 extern void hv_stimer_global_cleanup(void);
  33 extern void hv_stimer0_isr(void);
  34
  35 extern void hv_init_clocksource(void);
  36 extern void hv_remap_tsc_clocksource(void);
  37
  38 extern unsigned long hv_get_tsc_pfn(void);
  39 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
  40
  41 extern void hv_adj_sched_clock_offset(u64 offset);
  42
  43 static __always_inline bool
  44 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
  45                      u64 *cur_tsc, u64 *time)
  46 {
  47         u64 scale, offset;
  48         u32 sequence;
  49
  50         /*
  51          * The protocol for reading Hyper-V TSC page is specified in Hypervisor
  52          * Top-Level Functional Specification ver. 3.0 and above. To get the
  53          * reference time we must do the following:
  54          * - READ ReferenceTscSequence
  55          *   A special '0' value indicates the time source is unreliable and we
  56          *   need to use something else. The currently published specification
  57          *   versions (up to 4.0b) contain a mistake and wrongly claim '-1'
  58          *   instead of '0' as the special value, see commit c35b82ef0294.
  59          * - ReferenceTime =
  60          *        ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
  61          * - READ ReferenceTscSequence again. In case its value has changed
  62          *   since our first reading we need to discard ReferenceTime and repeat
  63          *   the whole sequence as the hypervisor was updating the page in
  64          *   between.
  65          */
  66         do {
  67                 sequence = READ_ONCE(tsc_pg->tsc_sequence);
  68                 if (!sequence)
  69                         return false;
  70                 /*
  71                  * Make sure we read sequence before we read other values from
  72                  * TSC page.
  73                  */
  74                 smp_rmb();
  75
  76                 scale = READ_ONCE(tsc_pg->tsc_scale);
  77                 offset = READ_ONCE(tsc_pg->tsc_offset);
  78                 *cur_tsc = hv_get_raw_timer();
  79
  80                 /*
  81                  * Make sure we read sequence after we read all other values
  82                  * from TSC page.
  83                  */
  84                 smp_rmb();
  85
  86         } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
  87
  88         *time = mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
  89         return true;
  90 }
  91
  92 #else /* CONFIG_HYPERV_TIMER */
  93 static inline unsigned long hv_get_tsc_pfn(void)
  94 {
  95         return 0;
  96 }
  97
  98 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
  99 {
 100         return NULL;
 101 }
 102
 103 static __always_inline bool
 104 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc, u64 *time)
 105 {
 106         return false;
 107 }
 108
 109 static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
 110 static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
 111 static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
 112 static inline void hv_stimer_global_cleanup(void) {}
 113 static inline void hv_stimer0_isr(void) {}
 114
 115 #endif /* CONFIG_HYPERV_TIMER */
 116
 117 #endif