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(void); 25 extern void hv_stimer_free(void); 26 extern int hv_stimer_cleanup(unsigned int cpu); 27 extern void hv_stimer_legacy_init(unsigned int cpu, int sint); 28 extern void hv_stimer_legacy_cleanup(unsigned int cpu); 29 extern void hv_stimer_global_cleanup(void); 30 extern void hv_stimer0_isr(void); 31 32 #ifdef CONFIG_HYPERV_TIMER 33 extern u64 (*hv_read_reference_counter)(void); 34 extern void hv_init_clocksource(void); 35 36 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void); 37 38 static inline notrace u64 39 hv_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 85 static inline notrace u64 86 hv_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 */ 94 static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void) 95 { 96 return NULL; 97 } 98 99 static 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