X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=arch%2Fpowerpc%2Fplatforms%2Fmaple%2Ftime.c;h=50bc4eb853535bca3e78eae519dbf98367b7f294;hb=987b0145d94eecf292d8b301228356f44611ab7c;hp=b9a2b3d4bf3323d6a04bf7f91f6f158d01b10030;hpb=f7ed79d23a47594e7834d66a8f14449796d4f3e6;p=linux-2.6.git

diff --git a/arch/powerpc/platforms/maple/time.c b/arch/powerpc/platforms/maple/time.c
index b9a2b3d4b..50bc4eb85 100644
--- a/arch/powerpc/platforms/maple/time.c
+++ b/arch/powerpc/platforms/maple/time.c
@@ -1,4 +1,6 @@
 /*
+ *  arch/ppc64/kernel/maple_time.c
+ *
  *  (c) Copyright 2004 Benjamin Herrenschmidt (benh@kernel.crashing.org),
  *                     IBM Corp. 
  *
@@ -60,14 +62,34 @@ static void maple_clock_write(unsigned long val, int addr)
 
 void maple_get_rtc_time(struct rtc_time *tm)
 {
-	do {
+	int uip, i;
+
+	/* The Linux interpretation of the CMOS clock register contents:
+	 * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
+	 * RTC registers show the second which has precisely just started.
+	 * Let's hope other operating systems interpret the RTC the same way.
+	 */
+
+	/* Since the UIP flag is set for about 2.2 ms and the clock
+	 * is typically written with a precision of 1 jiffy, trying
+	 * to obtain a precision better than a few milliseconds is
+	 * an illusion. Only consistency is interesting, this also
+	 * allows to use the routine for /dev/rtc without a potential
+	 * 1 second kernel busy loop triggered by any reader of /dev/rtc.
+	 */
+
+	for (i = 0; i<1000000; i++) {
+		uip = maple_clock_read(RTC_FREQ_SELECT);
 		tm->tm_sec = maple_clock_read(RTC_SECONDS);
 		tm->tm_min = maple_clock_read(RTC_MINUTES);
 		tm->tm_hour = maple_clock_read(RTC_HOURS);
 		tm->tm_mday = maple_clock_read(RTC_DAY_OF_MONTH);
 		tm->tm_mon = maple_clock_read(RTC_MONTH);
 		tm->tm_year = maple_clock_read(RTC_YEAR);
-	} while (tm->tm_sec != maple_clock_read(RTC_SECONDS));
+		uip |= maple_clock_read(RTC_FREQ_SELECT);
+		if ((uip & RTC_UIP)==0)
+			break;
+	}
 
 	if (!(maple_clock_read(RTC_CONTROL) & RTC_DM_BINARY)
 	    || RTC_ALWAYS_BCD) {