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 #ifdef CONFIG_HYPERV_TIMER
24 
25 /* Routines called by the VMbus driver */
26 extern int hv_stimer_alloc(bool have_percpu_irqs);
27 extern int hv_stimer_cleanup(unsigned int cpu);
28 extern void hv_stimer_legacy_init(unsigned int cpu, int sint);
29 extern void hv_stimer_legacy_cleanup(unsigned int cpu);
30 extern void hv_stimer_global_cleanup(void);
31 extern void hv_stimer0_isr(void);
32 
33 extern void hv_init_clocksource(void);
34 
35 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
36 
37 static inline notrace u64
38 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
39 {
40 	u64 scale, offset;
41 	u32 sequence;
42 
43 	/*
44 	 * The protocol for reading Hyper-V TSC page is specified in Hypervisor
45 	 * Top-Level Functional Specification ver. 3.0 and above. To get the
46 	 * reference time we must do the following:
47 	 * - READ ReferenceTscSequence
48 	 *   A special '0' value indicates the time source is unreliable and we
49 	 *   need to use something else. The currently published specification
50 	 *   versions (up to 4.0b) contain a mistake and wrongly claim '-1'
51 	 *   instead of '0' as the special value, see commit c35b82ef0294.
52 	 * - ReferenceTime =
53 	 *        ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
54 	 * - READ ReferenceTscSequence again. In case its value has changed
55 	 *   since our first reading we need to discard ReferenceTime and repeat
56 	 *   the whole sequence as the hypervisor was updating the page in
57 	 *   between.
58 	 */
59 	do {
60 		sequence = READ_ONCE(tsc_pg->tsc_sequence);
61 		if (!sequence)
62 			return U64_MAX;
63 		/*
64 		 * Make sure we read sequence before we read other values from
65 		 * TSC page.
66 		 */
67 		smp_rmb();
68 
69 		scale = READ_ONCE(tsc_pg->tsc_scale);
70 		offset = READ_ONCE(tsc_pg->tsc_offset);
71 		*cur_tsc = hv_get_raw_timer();
72 
73 		/*
74 		 * Make sure we read sequence after we read all other values
75 		 * from TSC page.
76 		 */
77 		smp_rmb();
78 
79 	} while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
80 
81 	return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
82 }
83 
84 static inline notrace u64
85 hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
86 {
87 	u64 cur_tsc;
88 
89 	return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
90 }
91 
92 #else /* CONFIG_HYPERV_TIMER */
93 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
94 {
95 	return NULL;
96 }
97 
98 static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
99 				       u64 *cur_tsc)
100 {
101 	return U64_MAX;
102 }
103 
104 static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
105 static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
106 static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
107 static inline void hv_stimer_global_cleanup(void) {}
108 static inline void hv_stimer0_isr(void) {}
109 
110 #endif /* CONFIG_HYPERV_TIMER */
111 
112 #endif
113