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>

diff --git a/include/linux/time.h b/include/linux/time.h
index 0015aea..dfbc4e8 100644 (file)
--- 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);

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index dfc7f87..b7a5841 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -28,6 +28,9 @@ static struct timekeeper timekeeper;
 /* flag for if timekeeping is suspended */
 int __read_mostly timekeeping_suspended;
 
+/* Flag for if there is a persistent clock on this platform */
+bool __read_mostly persistent_clock_exist = false;
+
 static inline void tk_normalize_xtime(struct timekeeper *tk)
 {
        while (tk->xtime_nsec >= ((u64)NSEC_PER_SEC << tk->shift)) {
@@ -609,12 +612,14 @@ void __init timekeeping_init(void)
        struct timespec now, boot, tmp;
 
        read_persistent_clock(&now);
+
        if (!timespec_valid_strict(&now)) {
                pr_warn("WARNING: Persistent clock returned invalid value!\n"
                        "         Check your CMOS/BIOS settings.\n");
                now.tv_sec = 0;
                now.tv_nsec = 0;
-       }
+       } else if (now.tv_sec || now.tv_nsec)
+               persistent_clock_exist = true;
 
        read_boot_clock(&boot);
        if (!timespec_valid_strict(&boot)) {
@@ -687,11 +692,12 @@ void timekeeping_inject_sleeptime(struct timespec *delta)
 {
        struct timekeeper *tk = &timekeeper;
        unsigned long flags;
-       struct timespec ts;
 
-       /* Make sure we don't set the clock twice */
-       read_persistent_clock(&ts);
-       if (!(ts.tv_sec == 0 && ts.tv_nsec == 0))
+       /*
+        * Make sure we don't set the clock twice, as timekeeping_resume()
+        * already did it
+        */
+       if (has_persistent_clock())
                return;
 
        write_seqlock_irqsave(&tk->lock, flags);