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