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 |
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(a: *cur_tsc, mul: scale, shift: 64) + offset; |
87 | return true; |
88 | } |
89 | |
90 | #else /* CONFIG_HYPERV_TIMER */ |
91 | static inline unsigned long hv_get_tsc_pfn(void) |
92 | { |
93 | return 0; |
94 | } |
95 | |
96 | static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void) |
97 | { |
98 | return NULL; |
99 | } |
100 | |
101 | static __always_inline bool |
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 | |
107 | static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; } |
108 | static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {} |
109 | static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {} |
110 | static inline void hv_stimer_global_cleanup(void) {} |
111 | static inline void hv_stimer0_isr(void) {} |
112 | |
113 | #endif /* CONFIG_HYPERV_TIMER */ |
114 | |
115 | #endif |
116 | |