timekeeping: Add persistent_clock_exist flag

In current kernel, there are several places which need to check
whether there is a persistent clock for the platform. Current check
is done by calling the read_persistent_clock() and validating its
return value.

So one optimization is to do the check only once in timekeeping_init(),
and use a flag persistent_clock_exist to record it.

v2: Add a has_persistent_clock() helper function, as suggested by John.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/time.h b/include/linux/time.h
index 0015aea4c4a..dfbc4e82e8b 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -115,6 +115,12 @@ static inline bool timespec_valid_strict(const struct timespec *ts)
 	return true;
 }
 
+extern bool persistent_clock_exist;
+static inline bool has_persistent_clock(void)
+{
+	return persistent_clock_exist;
+}
+
 extern void read_persistent_clock(struct timespec *ts);
 extern void read_boot_clock(struct timespec *ts);
 extern int update_persistent_clock(struct timespec now);