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