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