Check in new SN2 file from Jes' gettimeoffset() patch.

timer.c

+/*
+ * linux/arch/ia64/sn/kernel/sn2/timer.c
+ *
+ * Copyright (C) 2003 Silicon Graphics, Inc.
+ */
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/time.h>
+#include <linux/interrupt.h>
+
+#include <asm/hw_irq.h>
+#include <asm/system.h>
+
+#include <asm/sn/leds.h>
+#include <asm/sn/clksupport.h>
+
+
+extern unsigned long sn_rtc_cycles_per_second;
+static volatile unsigned long last_wall_rtc;
+
+/**
+ * gettimeoffset - number of nsecs elapsed since &xtime was last updated
+ *
+ * This function is used by do_gettimeofday() to determine the number
+ * of nsecs that have elapsed since the last update to &xtime.  On SN
+ * this is accomplished using the RTC built in to each Hub chip; each
+ * is guaranteed to be synchronized by the PROM, so a local read will
+ * suffice (GET_RTC_COUNTER() does this for us).  A snapshot of the RTC
+ * value is taken every time wall_jiffies is updated by the
+ * update_wall_time_hook (sn2_update_wall_time) which means we don't
+ * have to adjust for lost jiffies ticks or anything like that.
+ */
+
+static volatile long rtc_offset;
+static long rtc_nsecs_per_cycle;
+static long rtc_per_timer_tick;
+
+unsigned long
+sn_gettimeoffset(void)
+{
+	long current_rtc, elapsed_rtc, old, new_offset;
+
+	do {
+		old = rtc_offset;
+		current_rtc = GET_RTC_COUNTER();
+
+		/*
+		 * Need to address wrapping here!
+		 */
+		elapsed_rtc = (long)(current_rtc - last_wall_rtc);
+
+		new_offset = max(elapsed_rtc, old);
+	} while (cmpxchg(&rtc_offset, old, new_offset) != old);
+
+	return new_offset * rtc_nsecs_per_cycle;
+}
+
+
+void sn2_update_wall_time(long delta_nsec)
+{
+	rtc_offset -= min(rtc_offset, rtc_per_timer_tick);
+	last_wall_rtc = GET_RTC_COUNTER();
+}
+
+
+void sn2_reset_wall_time(void)
+{
+	rtc_offset = 0;
+	last_wall_rtc = GET_RTC_COUNTER();
+}
+
+
+void __init
+sn_timer_init(void)
+{
+	rtc_per_timer_tick = sn_rtc_cycles_per_second / HZ;
+	rtc_nsecs_per_cycle = 1000000000 / sn_rtc_cycles_per_second;
+
+	last_wall_rtc = GET_RTC_COUNTER();
+	update_wall_time_hook = sn2_update_wall_time;
+	reset_wall_time_hook = sn2_reset_wall_time;
+	gettimeoffset = sn_gettimeoffset;
+}