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