timekeeping: Add CONFIG_HAS_PERSISTENT_CLOCK option

Make the persistent clock check a kernel config option, so that some
platform can explicitely select it, also make CONFIG_RTC_HCTOSYS and
RTC_SYSTOHC depend on its non-existence, which could prevent the
persistent clock and RTC code from doing similar thing twice during
system's init/suspend/resume phases.

If the CONFIG_HAS_PERSISTENT_CLOCK=n, then no change happens for kernel
which still does the persistent clock check in timekeeping_init().

Cc: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Feng Tang <feng.tang@intel.com>
[jstultz: Added dependency for RTC_SYSTOHC as well]
Signed-off-by: John Stultz <john.stultz@linaro.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/time.h b/include/linux/time.h
index dfbc4e82e8ba..369b6e3b87d8 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -116,10 +116,15 @@ static inline bool timespec_valid_strict(const struct timespec *ts)
 }
 
 extern bool persistent_clock_exist;
+
+#ifdef CONFIG_HAS_PERSISTENT_CLOCK
+#define has_persistent_clock()  true
+#else
 static inline bool has_persistent_clock(void)
 {
         return persistent_clock_exist;
 }
+#endif
 
 extern void read_persistent_clock(struct timespec *ts);
 extern void read_boot_clock(struct timespec *ts);