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Subject[RFC PATCH v12 05/11] time: Add mechanism to recognize clocksource in time_get_snapshot
Date
From: Thomas Gleixner <tglx@linutronix.de>

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>
---
include/linux/clocksource.h | 6 ++++++
include/linux/clocksource_ids.h | 11 +++++++++++
include/linux/timekeeping.h | 12 +++++++-----
kernel/time/clocksource.c | 3 +++
kernel/time/timekeeping.c | 1 +
5 files changed, 28 insertions(+), 5 deletions(-)
create mode 100644 include/linux/clocksource_ids.h

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 86d143db6523..80d2a7e39630 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -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;

diff --git a/include/linux/clocksource_ids.h b/include/linux/clocksource_ids.h
new file mode 100644
index 000000000000..4d8e19e05328
--- /dev/null
+++ b/include/linux/clocksource_ids.h
@@ -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
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index b27e2ffa96c1..70e771862d20 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -3,6 +3,7 @@
#define _LINUX_TIMEKEEPING_H

#include <linux/errno.h>
+#include <linux/clocksource_ids.h>

/* Included from linux/ktime.h */

@@ -232,11 +233,12 @@ extern void timekeeping_inject_sleeptime64(const struct timespec64 *delta);
* @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;
};

/*
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 7cb09c4cf21c..a8f65b3e4ec8 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -928,6 +928,9 @@ 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;
+
#ifdef CONFIG_GENERIC_VDSO_CLOCK_MODE
if (cs->vdso_clock_mode < 0 ||
cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 9ebaab13339d..a2e46b0151b6 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -979,6 +979,7 @@ 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,
--
2.17.1
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