[linux-2.6-block.git] / include / clocksource / hyperv_timer.h

/* SPDX-License-Identifier: GPL-2.0 */

/*
 * Definitions for the clocksource provided by the Hyper-V
 * hypervisor to guest VMs, as described in the Hyper-V Top
 * Level Functional Spec (TLFS).
 *
 * Copyright (C) 2019, Microsoft, Inc.
 *
 * Author:  Michael Kelley <mikelley@microsoft.com>
 */

#ifndef __CLKSOURCE_HYPERV_TIMER_H
#define __CLKSOURCE_HYPERV_TIMER_H

#include <linux/clocksource.h>
#include <linux/math64.h>
#include <asm/mshyperv.h>

#define HV_MAX_MAX_DELTA_TICKS 0xffffffff
#define HV_MIN_DELTA_TICKS 1

/* Routines called by the VMbus driver */
extern int hv_stimer_alloc(int sint);
extern void hv_stimer_free(void);
extern void hv_stimer_init(unsigned int cpu);
extern void hv_stimer_cleanup(unsigned int cpu);
extern void hv_stimer_global_cleanup(void);
extern void hv_stimer0_isr(void);

#ifdef CONFIG_HYPERV_TIMER
extern struct clocksource *hyperv_cs;
extern void hv_init_clocksource(void);

extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);

static inline notrace u64
hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
{
	u64 scale, offset;
	u32 sequence;

	/*
	 * The protocol for reading Hyper-V TSC page is specified in Hypervisor
	 * Top-Level Functional Specification ver. 3.0 and above. To get the
	 * reference time we must do the following:
	 * - READ ReferenceTscSequence
	 *   A special '0' value indicates the time source is unreliable and we
	 *   need to use something else. The currently published specification
	 *   versions (up to 4.0b) contain a mistake and wrongly claim '-1'
	 *   instead of '0' as the special value, see commit c35b82ef0294.
	 * - ReferenceTime =
	 *        ((RDTSC() * ReferenceTscScale) >> 64) + ReferenceTscOffset
	 * - READ ReferenceTscSequence again. In case its value has changed
	 *   since our first reading we need to discard ReferenceTime and repeat
	 *   the whole sequence as the hypervisor was updating the page in
	 *   between.
	 */
	do {
		sequence = READ_ONCE(tsc_pg->tsc_sequence);
		if (!sequence)
			return U64_MAX;
		/*
		 * Make sure we read sequence before we read other values from
		 * TSC page.
		 */
		smp_rmb();

		scale = READ_ONCE(tsc_pg->tsc_scale);
		offset = READ_ONCE(tsc_pg->tsc_offset);
		*cur_tsc = hv_get_raw_timer();

		/*
		 * Make sure we read sequence after we read all other values
		 * from TSC page.
		 */
		smp_rmb();

	} while (READ_ONCE(tsc_pg->tsc_sequence) != sequence);

	return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset;
}

static inline notrace u64
hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
{
	u64 cur_tsc;

	return hv_read_tsc_page_tsc(tsc_pg, &cur_tsc);
}

#else /* CONFIG_HYPERV_TIMER */
static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
{
	return NULL;
}

static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
				       u64 *cur_tsc)
{
	return U64_MAX;
}
#endif /* CONFIG_HYPERV_TIMER */

#endif
Commit	Line	Data
fd1fea68 MK	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
dd2cb348 MK	16	#include <linux/clocksource.h>
	17	#include <linux/math64.h>
	18	#include <asm/mshyperv.h>
	19
fd1fea68 MK	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(int sint);
	25	extern void hv_stimer_free(void);
	26	extern void hv_stimer_init(unsigned int cpu);
	27	extern void hv_stimer_cleanup(unsigned int cpu);
	28	extern void hv_stimer_global_cleanup(void);
	29	extern void hv_stimer0_isr(void);
	30
3e2d9453	31	#ifdef CONFIG_HYPERV_TIMER
dd2cb348 MK	32	extern struct clocksource *hyperv_cs;
dd2cb348 MK	33	extern void hv_init_clocksource(void);
dd2cb348	34
dd2cb348 MK	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
3e2d9453	92	#else /* CONFIG_HYPERV_TIMER */
dd2cb348 MK	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	}
3e2d9453	103	#endif /* CONFIG_HYPERV_TIMER */
dd2cb348	104
fd1fea68	105	#endif