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 inline notrace u64
42 hv_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 
88 static inline notrace u64
89 hv_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 */
97 static inline unsigned long hv_get_tsc_pfn(void)
98 {
99 	return 0;
100 }
101 
102 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
103 {
104 	return NULL;
105 }
106 
107 static 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 
113 static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
114 static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
115 static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
116 static inline void hv_stimer_global_cleanup(void) {}
117 static inline void hv_stimer0_isr(void) {}
118 
119 #endif /* CONFIG_HYPERV_TIMER */
120 
121 #endif
122