---

yaml
---
r: 73900
b: refs/heads/master
c: bbbd999
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: c399da0d97e06803e51085ec076b63a3168aad1b
+refs/heads/master: bbbd99955bfe84c9ae63f51db946a7bcd21f48be

trunk/arch/x86/kernel/time_64.c

@@ -161,21 +161,27 @@ unsigned long read_persistent_clock(void)
 	unsigned century = 0;
 
 	spin_lock_irqsave(&rtc_lock, flags);
+	/*
+	 * if UIP is clear, then we have >= 244 microseconds before RTC
+	 * registers will be updated.  Spec sheet says that this is the
+	 * reliable way to read RTC - registers invalid (off bus) during update
+	 */
+	while ((CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
+		cpu_relax();
 
-	do {
-		sec = CMOS_READ(RTC_SECONDS);
-		min = CMOS_READ(RTC_MINUTES);
-		hour = CMOS_READ(RTC_HOURS);
-		day = CMOS_READ(RTC_DAY_OF_MONTH);
-		mon = CMOS_READ(RTC_MONTH);
-		year = CMOS_READ(RTC_YEAR);
+
+	/* now read all RTC registers while stable with interrupts disabled */
+	sec = CMOS_READ(RTC_SECONDS);
+	min = CMOS_READ(RTC_MINUTES);
+	hour = CMOS_READ(RTC_HOURS);
+	day = CMOS_READ(RTC_DAY_OF_MONTH);
+	mon = CMOS_READ(RTC_MONTH);
+	year = CMOS_READ(RTC_YEAR);
 #ifdef CONFIG_ACPI
-		if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
-					acpi_gbl_FADT.century)
-			century = CMOS_READ(acpi_gbl_FADT.century);
+	if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID &&
+				acpi_gbl_FADT.century)
+		century = CMOS_READ(acpi_gbl_FADT.century);
 #endif
-	} while (sec != CMOS_READ(RTC_SECONDS));
-
 	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	/*