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time: Add mechanism to recognize clocksource in time_get_snapshot

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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: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201209060932.212364-5-jianyong.wu@arm.com
This commit is contained in:
Thomas Gleixner 2020-12-09 14:09:27 +08:00 committed by Marc Zyngier
parent a8cf291bda
commit b2c67cbe9f
5 changed files with 27 additions and 5 deletions
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6
include/linux/clocksource.h
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@ -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;

11
include/linux/clocksource_ids.h Normal file
View File

@ -0,0 +1,11 @@
/* 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

12
include/linux/timekeeping.h
View File

@ -3,6 +3,7 @@
#define _LINUX_TIMEKEEPING_H
#include <linux/errno.h>
#include <linux/clocksource_ids.h>
/* Included from linux/ktime.h */
@ -243,11 +244,12 @@ struct ktime_timestamps {
* @cs_was_changed_seq: The sequence number of clocksource change events
*/
struct system_time_snapshot {
u64 cycles;
ktime_t real;
ktime_t raw;
unsigned int clock_was_set_seq;
u8 cs_was_changed_seq;
u64 cycles;
ktime_t real;
ktime_t raw;
enum clocksource_ids cs_id;
unsigned int clock_was_set_seq;
u8 cs_was_changed_seq;
};
/**

2
kernel/time/clocksource.c
View File

@ -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",

1
kernel/time/timekeeping.c
View File

@ -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,