1 files changed, 42 insertions, 1 deletions

diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index e6d0f9c1cafd..5b13fa029fd6 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -135,6 +135,14 @@ struct rtc_device {
         /* Some hardware can't support UIE mode */
         int uie_unsupported;
 
+        /* Number of nsec it takes to set the RTC clock. This influences when
+         * the set ops are called. An offset:
+         *   - of 0.5 s will call RTC set for wall clock time 10.0 s at 9.5 s
+         *   - of 1.5 s will call RTC set for wall clock time 10.0 s at 8.5 s
+         *   - of -0.5 s will call RTC set for wall clock time 10.0 s at 10.5 s
+         */
+        long set_offset_nsec;
+
         bool registered;
 
         struct nvmem_config *nvmem_config;
@@ -172,7 +180,7 @@ extern void devm_rtc_device_unregister(struct device *dev,
 
 extern int rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm);
 extern int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm);
-extern int rtc_set_ntp_time(struct timespec64 now);
+extern int rtc_set_ntp_time(struct timespec64 now, unsigned long *target_nsec);
 int __rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm);
 extern int rtc_read_alarm(struct rtc_device *rtc,
                         struct rtc_wkalrm *alrm);
@@ -221,6 +229,39 @@ static inline bool is_leap_year(unsigned int year)
         return (!(year % 4) && (year % 100)) || !(year % 400);
 }
 
+/* Determine if we can call to driver to set the time. Drivers can only be
+ * called to set a second aligned time value, and the field set_offset_nsec
+ * specifies how far away from the second aligned time to call the driver.
+ *
+ * This also computes 'to_set' which is the time we are trying to set, and has
+ * a zero in tv_nsecs, such that:
+ *    to_set - set_delay_nsec == now +/- FUZZ
+ *
+ */
+static inline bool rtc_tv_nsec_ok(s64 set_offset_nsec,
+                                  struct timespec64 *to_set,
+                                  const struct timespec64 *now)
+{
+        /* Allowed error in tv_nsec, arbitarily set to 5 jiffies in ns. */
+        const unsigned long TIME_SET_NSEC_FUZZ = TICK_NSEC * 5;
+        struct timespec64 delay = {.tv_sec = 0,
+                                   .tv_nsec = set_offset_nsec};
+
+        *to_set = timespec64_add(*now, delay);
+
+        if (to_set->tv_nsec < TIME_SET_NSEC_FUZZ) {
+                to_set->tv_nsec = 0;
+                return true;
+        }
+
+        if (to_set->tv_nsec > NSEC_PER_SEC - TIME_SET_NSEC_FUZZ) {
+                to_set->tv_sec++;
+                to_set->tv_nsec = 0;
+                return true;
+        }
+        return false;
+}
+
 #define rtc_register_device(device) \
         __rtc_register_device(THIS_MODULE, device)