Commit b2c67cbe authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Marc Zyngier
Browse files

time: Add mechanism to recognize clocksource in time_get_snapshot 



System time snapshots are not conveying information about the current
clocksource which was used, but callers like the PTP KVM guest
implementation have the requirement to evaluate the clocksource type to
select the appropriate mechanism.

Introduce a clocksource id field in struct clocksource which is by default
set to CSID_GENERIC (0). Clocksource implementations can set that field to
a value which allows to identify the clocksource.

Store the clocksource id of the current clocksource in the
system_time_snapshot so callers can evaluate which clocksource was used to
take the snapshot and act accordingly.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarJianyong Wu <jianyong.wu@arm.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201209060932.212364-5-jianyong.wu@arm.com
parent a8cf291b

include/linux/clocksource.h

+6 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#include <linux/timer.h>

#include <linux/init.h>

#include <linux/of.h>

#include <linux/clocksource_ids.h>

#include <asm/div64.h>

#include <asm/io.h>
@@ -62,6 +63,10 @@ struct module; 
 *			400-499: Perfect

 *				The ideal clocksource. A must-use where

 *				available.

 * @id:			Defaults to CSID_GENERIC. The id value is captured

 *			in certain snapshot functions to allow callers to

 *			validate the clocksource from which the snapshot was

 *			taken.

 * @flags:		Flags describing special properties

 * @enable:		Optional function to enable the clocksource

 * @disable:		Optional function to disable the clocksource
@@ -100,6 +105,7 @@ struct clocksource { 
	const char		*name;

	struct list_head	list;

	int			rating;

	enum clocksource_ids	id;

	enum vdso_clock_mode	vdso_clock_mode;

	unsigned long		flags;

include/linux/clocksource_ids.h

0 → 100644
+11 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef _LINUX_CLOCKSOURCE_IDS_H

#define _LINUX_CLOCKSOURCE_IDS_H



/* Enum to give clocksources a unique identifier */

enum clocksource_ids {

	CSID_GENERIC		= 0,

	CSID_MAX,

};



#endif

include/linux/timekeeping.h

+7 −5
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 
#define _LINUX_TIMEKEEPING_H



#include <linux/errno.h>

#include <linux/clocksource_ids.h>



/* Included from linux/ktime.h */
@@ -246,6 +247,7 @@ struct system_time_snapshot { 
	u64			cycles;

	ktime_t			real;

	ktime_t			raw;

	enum clocksource_ids	cs_id;

	unsigned int		clock_was_set_seq;

	u8			cs_was_changed_seq;

};

kernel/time/clocksource.c

+2 −0
Original line number Diff line number Diff line
@@ -920,6 +920,8 @@ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) 


	clocksource_arch_init(cs);



	if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))

		cs->id = CSID_GENERIC;

	if (cs->vdso_clock_mode < 0 ||

	    cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {

		pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",

kernel/time/timekeeping.c

+1 −0
Original line number Diff line number Diff line
@@ -1048,6 +1048,7 @@ void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot) 
	do {

		seq = read_seqcount_begin(&tk_core.seq);

		now = tk_clock_read(&tk->tkr_mono);

		systime_snapshot->cs_id = tk->tkr_mono.clock->id;

		systime_snapshot->cs_was_changed_seq = tk->cs_was_changed_seq;

		systime_snapshot->clock_was_set_seq = tk->clock_was_set_seq;

		base_real = ktime_add(tk->tkr_mono.base,