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 */
 28extern int hv_stimer_alloc(bool have_percpu_irqs);
 29extern int hv_stimer_cleanup(unsigned int cpu);
 30extern void hv_stimer_legacy_init(unsigned int cpu, int sint);
 31extern void hv_stimer_legacy_cleanup(unsigned int cpu);
 32extern void hv_stimer_global_cleanup(void);
 33extern void hv_stimer0_isr(void);
 34
 35extern void hv_init_clocksource(void);
 36extern void hv_remap_tsc_clocksource(void);
 37
 38extern unsigned long hv_get_tsc_pfn(void);
 39extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
 40
 41static __always_inline bool
 42hv_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 */
 91static inline unsigned long hv_get_tsc_pfn(void)
 92{
 93	return 0;
 94}
 95
 96static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
 97{
 98	return NULL;
 99}
100
101static __always_inline bool
102hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc, u64 *time)
103{
104	return false;
105}
106
107static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
108static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
109static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
110static inline void hv_stimer_global_cleanup(void) {}
111static inline void hv_stimer0_isr(void) {}
112
113#endif /* CONFIG_HYPERV_TIMER */
114
115#endif