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/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 */
  24 extern int hv_stimer_alloc(int sint);
  25 extern void hv_stimer_free(void);
  26 extern void hv_stimer_init(unsigned int cpu);
  27 extern void hv_stimer_cleanup(unsigned int cpu);
  28 extern void hv_stimer_global_cleanup(void);
  29 extern void hv_stimer0_isr(void);
  30
  31 #ifdef CONFIG_HYPERV_TIMER
  32 extern struct clocksource *hyperv_cs;
  33 extern void hv_init_clocksource(void);
  34
  35 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
  36
  37 static inline notrace u64
  38 hv_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
  84 static inline notrace u64
  85 hv_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 */
  93 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
  94 {
  95         return NULL;
  96 }
  97
  98 static 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