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