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