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 */
 24extern int hv_stimer_alloc(int sint);
 25extern void hv_stimer_free(void);
 26extern void hv_stimer_init(unsigned int cpu);
 27extern void hv_stimer_cleanup(unsigned int cpu);
 28extern void hv_stimer_global_cleanup(void);
 29extern void hv_stimer0_isr(void);
 30
 31#ifdef CONFIG_HYPERV_TIMER
 32extern struct clocksource *hyperv_cs;
 33extern void hv_init_clocksource(void);
 34
 35extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
 36
 37static inline notrace u64
 38hv_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
 84static inline notrace u64
 85hv_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 */
 93static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
 94{
 95	return NULL;
 96}
 97
 98static 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