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Subject[tip:timers/core] timekeeping: Introduce read_boot_clock
Commit-ID:  23970e389e9cee43c4b41023935e1417271708b2
Gitweb: http://git.kernel.org/tip/23970e389e9cee43c4b41023935e1417271708b2
Author: Martin Schwidefsky <schwidefsky@de.ibm.com>
AuthorDate: Fri, 14 Aug 2009 15:47:32 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 15 Aug 2009 10:55:47 +0200

timekeeping: Introduce read_boot_clock

Add the new function read_boot_clock to get the exact time the system
has been started. For architectures without support for exact boot
time a new weak function is added that returns 0. Use the exact boot
time to initialize wall_to_monotonic, or xtime if the read_boot_clock
returned 0.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134811.296703241@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>


---
arch/s390/kernel/time.c | 17 +++++------------
include/linux/time.h | 1 +
kernel/time/timekeeping.c | 24 ++++++++++++++++++++++--
3 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index a94ec48..6bff1a1 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -187,6 +187,11 @@ void read_persistent_clock(struct timespec *ts)
tod_to_timeval(get_clock() - TOD_UNIX_EPOCH, ts);
}

+void read_boot_clock(struct timespec *ts)
+{
+ tod_to_timeval(sched_clock_base_cc - TOD_UNIX_EPOCH, ts);
+}
+
static cycle_t read_tod_clock(struct clocksource *cs)
{
return get_clock();
@@ -243,9 +248,6 @@ void update_vsyscall_tz(void)
*/
void __init time_init(void)
{
- struct timespec ts;
- unsigned long flags;
-
/* Reset time synchronization interfaces. */
etr_reset();
stp_reset();
@@ -261,15 +263,6 @@ void __init time_init(void)
if (clocksource_register(&clocksource_tod) != 0)
panic("Could not register TOD clock source");

- /*
- * Reset wall_to_monotonic to the initial timestamp created
- * in head.S to get a precise value in /proc/uptime.
- */
- write_seqlock_irqsave(&xtime_lock, flags);
- tod_to_timeval(sched_clock_base_cc - TOD_UNIX_EPOCH, &ts);
- set_normalized_timespec(&wall_to_monotonic, -ts.tv_sec, -ts.tv_nsec);
- write_sequnlock_irqrestore(&xtime_lock, flags);
-
/* Enable TOD clock interrupts on the boot cpu. */
init_cpu_timer();

diff --git a/include/linux/time.h b/include/linux/time.h
index 53a3216..f505988 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -102,6 +102,7 @@ extern struct timespec wall_to_monotonic;
extern seqlock_t xtime_lock;

extern void read_persistent_clock(struct timespec *ts);
+extern void read_boot_clock(struct timespec *ts);
extern int update_persistent_clock(struct timespec now);
extern int no_sync_cmos_clock __read_mostly;
void timekeeping_init(void);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index f1a21ce..15e06de 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -501,6 +501,21 @@ void __attribute__((weak)) read_persistent_clock(struct timespec *ts)
ts->tv_nsec = 0;
}

+/**
+ * read_boot_clock - Return time of the system start.
+ *
+ * Weak dummy function for arches that do not yet support it.
+ * Function to read the exact time the system has been started.
+ * Returns a timespec with tv_sec=0 and tv_nsec=0 if unsupported.
+ *
+ * XXX - Do be sure to remove it once all arches implement it.
+ */
+void __attribute__((weak)) read_boot_clock(struct timespec *ts)
+{
+ ts->tv_sec = 0;
+ ts->tv_nsec = 0;
+}
+
/*
* timekeeping_init - Initializes the clocksource and common timekeeping values
*/
@@ -508,9 +523,10 @@ void __init timekeeping_init(void)
{
struct clocksource *clock;
unsigned long flags;
- struct timespec now;
+ struct timespec now, boot;

read_persistent_clock(&now);
+ read_boot_clock(&boot);

write_seqlock_irqsave(&xtime_lock, flags);

@@ -525,8 +541,12 @@ void __init timekeeping_init(void)
xtime.tv_nsec = now.tv_nsec;
raw_time.tv_sec = 0;
raw_time.tv_nsec = 0;
+ if (boot.tv_sec == 0 && boot.tv_nsec == 0) {
+ boot.tv_sec = xtime.tv_sec;
+ boot.tv_nsec = xtime.tv_nsec;
+ }
set_normalized_timespec(&wall_to_monotonic,
- -xtime.tv_sec, -xtime.tv_nsec);
+ -boot.tv_sec, -boot.tv_nsec);
update_xtime_cache(0);
total_sleep_time.tv_sec = 0;
total_sleep_time.tv_nsec = 0;

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