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 <hyperv/hvhdk.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_global_cleanup(void);
31
32 extern void hv_init_clocksource(void);
33 extern void hv_remap_tsc_clocksource(void);
34
35 extern unsigned long hv_get_tsc_pfn(void);
36 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
37
38 extern void hv_adj_sched_clock_offset(u64 offset);
39
40 static __always_inline bool
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page * tsc_pg,u64 * cur_tsc,u64 * time)41 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
42 u64 *cur_tsc, u64 *time)
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 false;
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 *time = mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
86 return true;
87 }
88
89 #else /* CONFIG_HYPERV_TIMER */
hv_get_tsc_pfn(void)90 static inline unsigned long hv_get_tsc_pfn(void)
91 {
92 return 0;
93 }
94
hv_get_tsc_page(void)95 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
96 {
97 return NULL;
98 }
99
100 static __always_inline bool
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page * tsc_pg,u64 * cur_tsc,u64 * time)101 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc, u64 *time)
102 {
103 return false;
104 }
105
hv_stimer_cleanup(unsigned int cpu)106 static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
hv_stimer_global_cleanup(void)107 static inline void hv_stimer_global_cleanup(void) {}
108
109 #endif /* CONFIG_HYPERV_TIMER */
110
111 #endif
112