linux 2.6.16.38 w/ vs2.0.3-rc1

[linux-2.6.git] / arch / powerpc / platforms / chrp / time.c

diff --git a/arch/powerpc/platforms/chrp/time.c b/arch/powerpc/platforms/chrp/time.c
index 7d78890..78df2e7 100644 (file)
--- 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);