linux 2.6.16.38 w/ vs2.0.3-rc1

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

diff --git a/arch/powerpc/platforms/maple/time.c b/arch/powerpc/platforms/maple/time.c
index 9f7579b..50bc4eb 100644 (file)
--- 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. 
  *
@@ -11,6 +13,7 @@
 
 #undef DEBUG
 
+#include <linux/config.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
 #include <linux/kernel.h>
@@ -59,14 +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) {