1 /* SPDX-License-Identifier: GPL-2.0 */
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).
8 * Copyright (C) 2019, Microsoft, Inc.
10 * Author: Michael Kelley <mikelley@microsoft.com>
13 #ifndef __CLKSOURCE_HYPERV_TIMER_H
14 #define __CLKSOURCE_HYPERV_TIMER_H
16 #include <linux/clocksource.h>
17 #include <linux/math64.h>
18 #include <asm/mshyperv.h>
20 #define HV_MAX_MAX_DELTA_TICKS 0xffffffff
21 #define HV_MIN_DELTA_TICKS 1
23 /* Routines called by the VMbus driver */
24 extern int hv_stimer_alloc(int sint);
25 extern void hv_stimer_free(void);
26 extern void hv_stimer_init(unsigned int cpu);
27 extern void hv_stimer_cleanup(unsigned int cpu);
28 extern void hv_stimer_global_cleanup(void);
29 extern void hv_stimer0_isr(void);
31 #if IS_ENABLED(CONFIG_HYPERV)
32 extern struct clocksource *hyperv_cs;
33 extern void hv_init_clocksource(void);
34 #endif /* CONFIG_HYPERV */
36 #ifdef CONFIG_HYPERV_TSCPAGE
37 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
39 static inline notrace u64
40 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
46 * The protocol for reading Hyper-V TSC page is specified in Hypervisor
47 * Top-Level Functional Specification ver. 3.0 and above. To get the
48 * reference time we must do the following:
49 * - READ ReferenceTscSequence
50 * A special '0' value indicates the time source is unreliable and we
51 * need to use something else. The currently published specification
52 * versions (up to 4.0b) contain a mistake and wrongly claim '-1'
53 * instead of '0' as the special value, see commit c35b82ef0294.
55 * ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
56 * - READ ReferenceTscSequence again. In case its value has changed
57 * since our first reading we need to discard ReferenceTime and repeat
58 * the whole sequence as the hypervisor was updating the page in
62 sequence = READ_ONCE(tsc_pg->tsc_sequence);
66 * Make sure we read sequence before we read other values from
71 scale = READ_ONCE(tsc_pg->tsc_scale);
72 offset = READ_ONCE(tsc_pg->tsc_offset);
73 *cur_tsc = hv_get_raw_timer();
76 * Make sure we read sequence after we read all other values
81 } while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);
83 return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
86 static inline notrace u64
87 hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
91 return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
94 #else /* CONFIG_HYPERV_TSC_PAGE */
95 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
100 static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
105 #endif /* CONFIG_HYPERV_TSCPAGE */