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(*cur_tsc, scale, 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