X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;ds=inline;f=arch%2Fpowerpc%2Fplatforms%2Fchrp%2Ftime.c;fp=arch%2Fpowerpc%2Fplatforms%2Fchrp%2Ftime.c;h=78df2e7ca88a1c9d5edc76e54ad7f9102420dd2e;hb=64ba3f394c830ec48a1c31b53dcae312c56f1604;hp=7d7889026936a2eee1366b4ba7e6cc6b9e35923c;hpb=be1e6109ac94a859551f8e1774eb9a8469fe055c;p=linux-2.6.git

diff --git a/arch/powerpc/platforms/chrp/time.c b/arch/powerpc/platforms/chrp/time.c
index 7d7889026..78df2e7ca 100644
--- a/arch/powerpc/platforms/chrp/time.c
+++ b/arch/powerpc/platforms/chrp/time.c
@@ -1,4 +1,6 @@
 /*
+ *  arch/ppc/platforms/chrp_time.c
+ *
  *  Copyright (C) 1991, 1992, 1995  Linus Torvalds
  *
  * Adapted for PowerPC (PReP) by Gary Thomas
@@ -120,15 +122,33 @@ int chrp_set_rtc_time(struct rtc_time *tmarg)
 void chrp_get_rtc_time(struct rtc_time *tm)
 {
 	unsigned int year, mon, day, hour, min, sec;
+	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.
+	 */
 
-	do {
+	/* 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 = chrp_cmos_clock_read(RTC_FREQ_SELECT);
 		sec = chrp_cmos_clock_read(RTC_SECONDS);
 		min = chrp_cmos_clock_read(RTC_MINUTES);
 		hour = chrp_cmos_clock_read(RTC_HOURS);
 		day = chrp_cmos_clock_read(RTC_DAY_OF_MONTH);
 		mon = chrp_cmos_clock_read(RTC_MONTH);
 		year = chrp_cmos_clock_read(RTC_YEAR);
-	} while (sec != chrp_cmos_clock_read(RTC_SECONDS));
+		uip |= chrp_cmos_clock_read(RTC_FREQ_SELECT);
+		if ((uip & RTC_UIP)==0) break;
+	}
 
 	if (!(chrp_cmos_clock_read(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
 		BCD_TO_BIN(sec);