ntp: Consolidate the RTC update implementation

The code for the legacy RTC and the RTC class based update are pretty much
the same. Consolidate the common parts into one function and just invoke
the actual setter functions.

For RTC class based devices the update code checks whether the offset is
valid for the device, which is usually not the case for the first
invocation. If it's not the same it stores the correct offset and lets the
caller try again. That's not much different from the previous approach
where the first invocation had a pretty low probability to actually hit the
allowed window.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201206220542.355743355@linutronix.de

kernel/time/ntp.c

@@ -564,118 +564,53 @@ static inline bool rtc_tv_nsec_ok(unsigned long set_offset_nsec,
 	return false;
 }
 
+#ifdef CONFIG_GENERIC_CMOS_UPDATE
+int __weak update_persistent_clock64(struct timespec64 now64)
+{
+	return -ENODEV;
+}
+#else
+static inline int update_persistent_clock64(struct timespec64 now64)
+{
+	return -ENODEV;
+}
+#endif
+
 #ifdef CONFIG_RTC_SYSTOHC
-/*
- * rtc_set_ntp_time - Save NTP synchronized time to the RTC
- */
-static int rtc_set_ntp_time(struct timespec64 now, unsigned long *offset_nsec)
+/* Save NTP synchronized time to the RTC */
+static int update_rtc(struct timespec64 *to_set, unsigned long *offset_nsec)
 {
-	struct timespec64 to_set;
 	struct rtc_device *rtc;
 	struct rtc_time tm;
 	int err = -ENODEV;
-	bool ok;
 
 	rtc = rtc_class_open(CONFIG_RTC_SYSTOHC_DEVICE);
 	if (!rtc)
-		goto out_err;
+		return -ENODEV;
 
 	if (!rtc->ops || !rtc->ops->set_time)
 		goto out_close;
 
-	/* Store the update offset for this RTC */
+	/* First call might not have the correct offset */
+	if (*offset_nsec == rtc->set_offset_nsec) {
+		rtc_time64_to_tm(to_set->tv_sec, &tm);
+		err = rtc_set_time(rtc, &tm);
+	} else {
+		/* Store the update offset and let the caller try again */
 		*offset_nsec = rtc->set_offset_nsec;
-
-	ok = rtc_tv_nsec_ok(rtc->set_offset_nsec, &to_set, &now);
-	if (!ok) {
-		err = -EPROTO;
-		goto out_close;
+		err = -EAGAIN;
 	}
-
-	rtc_time64_to_tm(to_set.tv_sec, &tm);
-
-	err = rtc_set_time(rtc, &tm);
-
 out_close:
 	rtc_class_close(rtc);
-out_err:
 	return err;
 }
-
-static void sync_rtc_clock(void)
-{
-	unsigned long offset_nsec;
-	struct timespec64 adjust;
-	int rc;
-
-	ktime_get_real_ts64(&adjust);
-
-	if (persistent_clock_is_local)
-		adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
-
-	/*
-	 * The current RTC in use will provide the nanoseconds offset prior
-	 * to a full second it wants to be called at, and invokes
-	 * rtc_tv_nsec_ok() internally.
-	 */
-	rc = rtc_set_ntp_time(adjust, &offset_nsec);
-	if (rc == -ENODEV)
-		return;
-
-	sched_sync_hw_clock(offset_nsec, rc != 0);
-}
 #else
-static inline void sync_rtc_clock(void) { }
-#endif
-
-#ifdef CONFIG_GENERIC_CMOS_UPDATE
-int __weak update_persistent_clock64(struct timespec64 now64)
+static inline int update_rtc(struct timespec64 *to_set, unsigned long *offset_nsec)
 {
 	return -ENODEV;
 }
 #endif
 
-static bool sync_cmos_clock(void)
-{
-	static bool no_cmos;
-	struct timespec64 now;
-	struct timespec64 adjust;
-	int rc = -EPROTO;
-	long target_nsec = NSEC_PER_SEC / 2;
-
-	if (!IS_ENABLED(CONFIG_GENERIC_CMOS_UPDATE))
-		return false;
-
-	if (no_cmos)
-		return false;
-
-	/*
-	 * Historically update_persistent_clock64() has followed x86
-	 * semantics, which match the MC146818A/etc RTC. This RTC will store
-	 * 'adjust' and then in .5s it will advance once second.
-	 *
-	 * Architectures are strongly encouraged to use rtclib and not
-	 * implement this legacy API.
-	 */
-	ktime_get_real_ts64(&now);
-	if (rtc_tv_nsec_ok(target_nsec, &adjust, &now)) {
-		if (persistent_clock_is_local)
-			adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
-		rc = update_persistent_clock64(adjust);
-		/*
-		 * The machine does not support update_persistent_clock64 even
-		 * though it defines CONFIG_GENERIC_CMOS_UPDATE.
-		 */
-		if (rc == -ENODEV) {
-			no_cmos = true;
-			return false;
-		}
-	}
-
-	sched_sync_hw_clock(target_nsec, rc != 0);
-	return true;
-}
-
 /*
  * If we have an externally synchronized Linux clock, then update RTC clock
  * accordingly every ~11 minutes. Generally RTCs can only store second
@@ -686,6 +621,15 @@ static bool sync_cmos_clock(void)
  */
 static void sync_hw_clock(struct work_struct *work)
 {
+	/*
+	 * The default synchronization offset is 500ms for the deprecated
+	 * update_persistent_clock64() under the assumption that it uses
+	 * the infamous CMOS clock (MC146818).
+	 */
+	static unsigned long offset_nsec = NSEC_PER_SEC / 2;
+	struct timespec64 now, to_set;
+	int res = -EAGAIN;
+
 	/*
 	 * Don't update if STA_UNSYNC is set and if ntp_notify_cmos_timer()
 	 * managed to schedule the work between the timer firing and the
@@ -694,10 +638,26 @@ static void sync_hw_clock(struct work_struct *work)
 	if (!ntp_synced() || hrtimer_is_queued(&sync_hrtimer))
 		return;
 
-	if (sync_cmos_clock())
-		return;
+	ktime_get_real_ts64(&now);
+	/* If @now is not in the allowed window, try again */
+	if (!rtc_tv_nsec_ok(offset_nsec, &to_set, &now))
+		goto rearm;
 
-	sync_rtc_clock();
+	/* Take timezone adjusted RTCs into account */
+	if (persistent_clock_is_local)
+		to_set.tv_sec -= (sys_tz.tz_minuteswest * 60);
+
+	/* Try the legacy RTC first. */
+	res = update_persistent_clock64(to_set);
+	if (res != -ENODEV)
+		goto rearm;
+
+	/* Try the RTC class */
+	res = update_rtc(&to_set, &offset_nsec);
+	if (res == -ENODEV)
+		return;
+rearm:
+	sched_sync_hw_clock(offset_nsec, res != 0);
 }
 
 void ntp_notify_cmos_timer(void)