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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/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 */
28extern int hv_stimer_alloc(bool have_percpu_irqs);
29extern int hv_stimer_cleanup(unsigned int cpu);
30extern void hv_stimer_legacy_init(unsigned int cpu, int sint);
31extern void hv_stimer_legacy_cleanup(unsigned int cpu);
32extern void hv_stimer_global_cleanup(void);
33extern void hv_stimer0_isr(void);
34
35extern void hv_init_clocksource(void);
36extern void hv_remap_tsc_clocksource(void);
37
38extern unsigned long hv_get_tsc_pfn(void);
39extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
40
41static inline notrace u64
42hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
43{
44 u64 scale, offset;
45 u32 sequence;
46
47 /*
48 * The protocol for reading Hyper-V TSC page is specified in Hypervisor
49 * Top-Level Functional Specification ver. 3.0 and above. To get the
50 * reference time we must do the following:
51 * - READ ReferenceTscSequence
52 * A special '0' value indicates the time source is unreliable and we
53 * need to use something else. The currently published specification
54 * versions (up to 4.0b) contain a mistake and wrongly claim '-1'
55 * instead of '0' as the special value, see commit c35b82ef0294.
56 * - ReferenceTime =
57 * ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
58 * - READ ReferenceTscSequence again. In case its value has changed
59 * since our first reading we need to discard ReferenceTime and repeat
60 * the whole sequence as the hypervisor was updating the page in
61 * between.
62 */
63 do {
64 sequence = READ_ONCE(tsc_pg->tsc_sequence);
65 if (!sequence)
66 return U64_MAX;
67 /*
68 * Make sure we read sequence before we read other values from
69 * TSC page.
70 */
71 smp_rmb();
72
73 scale = READ_ONCE(tsc_pg->tsc_scale);
74 offset = READ_ONCE(tsc_pg->tsc_offset);
75 *cur_tsc = hv_get_raw_timer();
76
77 /*
78 * Make sure we read sequence after we read all other values
79 * from TSC page.
80 */
81 smp_rmb();
82
83 } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
84
85 return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
86}
87
88static inline notrace u64
89hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
90{
91 u64 cur_tsc;
92
93 return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
94}
95
96#else /* CONFIG_HYPERV_TIMER */
97static inline unsigned long hv_get_tsc_pfn(void)
98{
99 return 0;
100}
101
102static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
103{
104 return NULL;
105}
106
107static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
108 u64 *cur_tsc)
109{
110 return U64_MAX;
111}
112
113static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
114static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
115static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
116static inline void hv_stimer_global_cleanup(void) {}
117static inline void hv_stimer0_isr(void) {}
118
119#endif /* CONFIG_HYPERV_TIMER */
120
121#endif