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