Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 641 insertions, 0 deletions

diff --git a/arch/sparc/kernel/time.c b/arch/sparc/kernel/time.c
new file mode 100644
index 000000000000..6486cbf2efe9
--- /dev/null
+++ b/arch/sparc/kernel/time.c
@@ -0,0 +1,641 @@
+/* $Id: time.c,v 1.60 2002/01/23 14:33:55 davem Exp $
+ * linux/arch/sparc/kernel/time.c
+ *
+ * Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
+ * Copyright (C) 1996 Thomas K. Dyas (tdyas@eden.rutgers.edu)
+ *
+ * Chris Davis (cdavis@cois.on.ca) 03/27/1998
+ * Added support for the intersil on the sun4/4200
+ *
+ * Gleb Raiko (rajko@mech.math.msu.su) 08/18/1998
+ * Support for MicroSPARC-IIep, PCI CPU.
+ *
+ * This file handles the Sparc specific time handling details.
+ *
+ * 1997-09-10	Updated NTP code according to technical memorandum Jan '96
+ *		"A Kernel Model for Precision Timekeeping" by Dave Mills
+ */
+#include <linux/config.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/param.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/interrupt.h>
+#include <linux/time.h>
+#include <linux/timex.h>
+#include <linux/init.h>
+#include <linux/pci.h>
+#include <linux/ioport.h>
+#include <linux/profile.h>
+
+#include <asm/oplib.h>
+#include <asm/segment.h>
+#include <asm/timer.h>
+#include <asm/mostek.h>
+#include <asm/system.h>
+#include <asm/irq.h>
+#include <asm/io.h>
+#include <asm/idprom.h>
+#include <asm/machines.h>
+#include <asm/sun4paddr.h>
+#include <asm/page.h>
+#include <asm/pcic.h>
+
+extern unsigned long wall_jiffies;
+
+u64 jiffies_64 = INITIAL_JIFFIES;
+
+EXPORT_SYMBOL(jiffies_64);
+
+DEFINE_SPINLOCK(rtc_lock);
+enum sparc_clock_type sp_clock_typ;
+DEFINE_SPINLOCK(mostek_lock);
+void __iomem *mstk48t02_regs = NULL;
+static struct mostek48t08 *mstk48t08_regs = NULL;
+static int set_rtc_mmss(unsigned long);
+static int sbus_do_settimeofday(struct timespec *tv);
+
+#ifdef CONFIG_SUN4
+struct intersil *intersil_clock;
+#define intersil_cmd(intersil_reg, intsil_cmd) intersil_reg->int_cmd_reg = \
+	(intsil_cmd)
+
+#define intersil_intr(intersil_reg, intsil_cmd) intersil_reg->int_intr_reg = \
+	(intsil_cmd)
+
+#define intersil_start(intersil_reg) intersil_cmd(intersil_reg, \
+	( INTERSIL_START | INTERSIL_32K | INTERSIL_NORMAL | INTERSIL_24H |\
+	  INTERSIL_INTR_ENABLE))
+
+#define intersil_stop(intersil_reg) intersil_cmd(intersil_reg, \
+	( INTERSIL_STOP | INTERSIL_32K | INTERSIL_NORMAL | INTERSIL_24H |\
+	  INTERSIL_INTR_ENABLE))
+
+#define intersil_read_intr(intersil_reg, towhere) towhere = \
+	intersil_reg->int_intr_reg
+
+#endif
+
+unsigned long profile_pc(struct pt_regs *regs)
+{
+	extern char __copy_user_begin[], __copy_user_end[];
+	extern char __atomic_begin[], __atomic_end[];
+	extern char __bzero_begin[], __bzero_end[];
+	extern char __bitops_begin[], __bitops_end[];
+
+	unsigned long pc = regs->pc;
+
+	if (in_lock_functions(pc) ||
+	    (pc >= (unsigned long) __copy_user_begin &&
+	     pc < (unsigned long) __copy_user_end) ||
+	    (pc >= (unsigned long) __atomic_begin &&
+	     pc < (unsigned long) __atomic_end) ||
+	    (pc >= (unsigned long) __bzero_begin &&
+	     pc < (unsigned long) __bzero_end) ||
+	    (pc >= (unsigned long) __bitops_begin &&
+	     pc < (unsigned long) __bitops_end))
+		pc = regs->u_regs[UREG_RETPC];
+	return pc;
+}
+
+__volatile__ unsigned int *master_l10_counter;
+__volatile__ unsigned int *master_l10_limit;
+
+/*
+ * timer_interrupt() needs to keep up the real-time clock,
+ * as well as call the "do_timer()" routine every clocktick
+ */
+
+#define TICK_SIZE (tick_nsec / 1000)
+
+irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs * regs)
+{
+	/* last time the cmos clock got updated */
+	static long last_rtc_update;
+
+#ifndef CONFIG_SMP
+	profile_tick(CPU_PROFILING, regs);
+#endif
+
+	/* Protect counter clear so that do_gettimeoffset works */
+	write_seqlock(&xtime_lock);
+#ifdef CONFIG_SUN4
+	if((idprom->id_machtype == (SM_SUN4 | SM_4_260)) ||
+	   (idprom->id_machtype == (SM_SUN4 | SM_4_110))) {
+		int temp;
+        	intersil_read_intr(intersil_clock, temp);
+		/* re-enable the irq */
+		enable_pil_irq(10);
+	}
+#endif
+	clear_clock_irq();
+
+	do_timer(regs);
+#ifndef CONFIG_SMP
+	update_process_times(user_mode(regs));
+#endif
+
+
+	/* Determine when to update the Mostek clock. */
+	if ((time_status & STA_UNSYNC) == 0 &&
+	    xtime.tv_sec > last_rtc_update + 660 &&
+	    (xtime.tv_nsec / 1000) >= 500000 - ((unsigned) TICK_SIZE) / 2 &&
+	    (xtime.tv_nsec / 1000) <= 500000 + ((unsigned) TICK_SIZE) / 2) {
+	  if (set_rtc_mmss(xtime.tv_sec) == 0)
+	    last_rtc_update = xtime.tv_sec;
+	  else
+	    last_rtc_update = xtime.tv_sec - 600; /* do it again in 60 s */
+	}
+	write_sequnlock(&xtime_lock);
+
+	return IRQ_HANDLED;
+}
+
+/* Kick start a stopped clock (procedure from the Sun NVRAM/hostid FAQ). */
+static void __init kick_start_clock(void)
+{
+	struct mostek48t02 *regs = (struct mostek48t02 *)mstk48t02_regs;
+	unsigned char sec;
+	int i, count;
+
+	prom_printf("CLOCK: Clock was stopped. Kick start ");
+
+	spin_lock_irq(&mostek_lock);
+
+	/* Turn on the kick start bit to start the oscillator. */
+	regs->creg |= MSTK_CREG_WRITE;
+	regs->sec &= ~MSTK_STOP;
+	regs->hour |= MSTK_KICK_START;
+	regs->creg &= ~MSTK_CREG_WRITE;
+
+	spin_unlock_irq(&mostek_lock);
+
+	/* Delay to allow the clock oscillator to start. */
+	sec = MSTK_REG_SEC(regs);
+	for (i = 0; i < 3; i++) {
+		while (sec == MSTK_REG_SEC(regs))
+			for (count = 0; count < 100000; count++)
+				/* nothing */ ;
+		prom_printf(".");
+		sec = regs->sec;
+	}
+	prom_printf("\n");
+
+	spin_lock_irq(&mostek_lock);
+
+	/* Turn off kick start and set a "valid" time and date. */
+	regs->creg |= MSTK_CREG_WRITE;
+	regs->hour &= ~MSTK_KICK_START;
+	MSTK_SET_REG_SEC(regs,0);
+	MSTK_SET_REG_MIN(regs,0);
+	MSTK_SET_REG_HOUR(regs,0);
+	MSTK_SET_REG_DOW(regs,5);
+	MSTK_SET_REG_DOM(regs,1);
+	MSTK_SET_REG_MONTH(regs,8);
+	MSTK_SET_REG_YEAR(regs,1996 - MSTK_YEAR_ZERO);
+	regs->creg &= ~MSTK_CREG_WRITE;
+
+	spin_unlock_irq(&mostek_lock);
+
+	/* Ensure the kick start bit is off. If it isn't, turn it off. */
+	while (regs->hour & MSTK_KICK_START) {
+		prom_printf("CLOCK: Kick start still on!\n");
+
+		spin_lock_irq(&mostek_lock);
+		regs->creg |= MSTK_CREG_WRITE;
+		regs->hour &= ~MSTK_KICK_START;
+		regs->creg &= ~MSTK_CREG_WRITE;
+		spin_unlock_irq(&mostek_lock);
+	}
+
+	prom_printf("CLOCK: Kick start procedure successful.\n");
+}
+
+/* Return nonzero if the clock chip battery is low. */
+static __inline__ int has_low_battery(void)
+{
+	struct mostek48t02 *regs = (struct mostek48t02 *)mstk48t02_regs;
+	unsigned char data1, data2;
+
+	spin_lock_irq(&mostek_lock);
+	data1 = regs->eeprom[0];	/* Read some data. */
+	regs->eeprom[0] = ~data1;	/* Write back the complement. */
+	data2 = regs->eeprom[0];	/* Read back the complement. */
+	regs->eeprom[0] = data1;	/* Restore the original value. */
+	spin_unlock_irq(&mostek_lock);
+
+	return (data1 == data2);	/* Was the write blocked? */
+}
+
+/* Probe for the real time clock chip on Sun4 */
+static __inline__ void sun4_clock_probe(void)
+{
+#ifdef CONFIG_SUN4
+	int temp;
+	struct resource r;
+
+	memset(&r, 0, sizeof(r));
+	if( idprom->id_machtype == (SM_SUN4 | SM_4_330) ) {
+		sp_clock_typ = MSTK48T02;
+		r.start = sun4_clock_physaddr;
+		mstk48t02_regs = sbus_ioremap(&r, 0,
+				       sizeof(struct mostek48t02), NULL);
+		mstk48t08_regs = NULL;  /* To catch weirdness */
+		intersil_clock = NULL;  /* just in case */
+
+		/* Kick start the clock if it is completely stopped. */
+		if (mostek_read(mstk48t02_regs + MOSTEK_SEC) & MSTK_STOP)
+			kick_start_clock();
+	} else if( idprom->id_machtype == (SM_SUN4 | SM_4_260)) {
+		/* intersil setup code */
+		printk("Clock: INTERSIL at %8x ",sun4_clock_physaddr);
+		sp_clock_typ = INTERSIL;
+		r.start = sun4_clock_physaddr;
+		intersil_clock = (struct intersil *) 
+		    sbus_ioremap(&r, 0, sizeof(*intersil_clock), "intersil");
+		mstk48t02_regs = 0;  /* just be sure */
+		mstk48t08_regs = NULL;  /* ditto */
+		/* initialise the clock */
+
+		intersil_intr(intersil_clock,INTERSIL_INT_100HZ);
+
+		intersil_start(intersil_clock);
+
+		intersil_read_intr(intersil_clock, temp);
+                while (!(temp & 0x80))
+                        intersil_read_intr(intersil_clock, temp);
+
+                intersil_read_intr(intersil_clock, temp);
+                while (!(temp & 0x80))
+                        intersil_read_intr(intersil_clock, temp);
+
+		intersil_stop(intersil_clock);
+
+	}
+#endif
+}
+
+/* Probe for the mostek real time clock chip. */
+static __inline__ void clock_probe(void)
+{
+	struct linux_prom_registers clk_reg[2];
+	char model[128];
+	register int node, cpuunit, bootbus;
+	struct resource r;
+
+	cpuunit = bootbus = 0;
+	memset(&r, 0, sizeof(r));
+
+	/* Determine the correct starting PROM node for the probe. */
+	node = prom_getchild(prom_root_node);
+	switch (sparc_cpu_model) {
+	case sun4c:
+		break;
+	case sun4m:
+		node = prom_getchild(prom_searchsiblings(node, "obio"));
+		break;
+	case sun4d:
+		node = prom_getchild(bootbus = prom_searchsiblings(prom_getchild(cpuunit = prom_searchsiblings(node, "cpu-unit")), "bootbus"));
+		break;
+	default:
+		prom_printf("CLOCK: Unsupported architecture!\n");
+		prom_halt();
+	}
+
+	/* Find the PROM node describing the real time clock. */
+	sp_clock_typ = MSTK_INVALID;
+	node = prom_searchsiblings(node,"eeprom");
+	if (!node) {
+		prom_printf("CLOCK: No clock found!\n");
+		prom_halt();
+	}
+
+	/* Get the model name and setup everything up. */
+	model[0] = '\0';
+	prom_getstring(node, "model", model, sizeof(model));
+	if (strcmp(model, "mk48t02") == 0) {
+		sp_clock_typ = MSTK48T02;
+		if (prom_getproperty(node, "reg", (char *) clk_reg, sizeof(clk_reg)) == -1) {
+			prom_printf("clock_probe: FAILED!\n");
+			prom_halt();
+		}
+		if (sparc_cpu_model == sun4d)
+			prom_apply_generic_ranges (bootbus, cpuunit, clk_reg, 1);
+		else
+			prom_apply_obio_ranges(clk_reg, 1);
+		/* Map the clock register io area read-only */
+		r.flags = clk_reg[0].which_io;
+		r.start = clk_reg[0].phys_addr;
+		mstk48t02_regs = sbus_ioremap(&r, 0,
+		    sizeof(struct mostek48t02), "mk48t02");
+		mstk48t08_regs = NULL;  /* To catch weirdness */
+	} else if (strcmp(model, "mk48t08") == 0) {
+		sp_clock_typ = MSTK48T08;
+		if(prom_getproperty(node, "reg", (char *) clk_reg,
+				    sizeof(clk_reg)) == -1) {
+			prom_printf("clock_probe: FAILED!\n");
+			prom_halt();
+		}
+		if (sparc_cpu_model == sun4d)
+			prom_apply_generic_ranges (bootbus, cpuunit, clk_reg, 1);
+		else
+			prom_apply_obio_ranges(clk_reg, 1);
+		/* Map the clock register io area read-only */
+		/* XXX r/o attribute is somewhere in r.flags */
+		r.flags = clk_reg[0].which_io;
+		r.start = clk_reg[0].phys_addr;
+		mstk48t08_regs = (struct mostek48t08 *) sbus_ioremap(&r, 0,
+		    sizeof(struct mostek48t08), "mk48t08");
+
+		mstk48t02_regs = &mstk48t08_regs->regs;
+	} else {
+		prom_printf("CLOCK: Unknown model name '%s'\n",model);
+		prom_halt();
+	}
+
+	/* Report a low battery voltage condition. */
+	if (has_low_battery())
+		printk(KERN_CRIT "NVRAM: Low battery voltage!\n");
+
+	/* Kick start the clock if it is completely stopped. */
+	if (mostek_read(mstk48t02_regs + MOSTEK_SEC) & MSTK_STOP)
+		kick_start_clock();
+}
+
+void __init sbus_time_init(void)
+{
+	unsigned int year, mon, day, hour, min, sec;
+	struct mostek48t02 *mregs;
+
+#ifdef CONFIG_SUN4
+	int temp;
+	struct intersil *iregs;
+#endif
+
+	BTFIXUPSET_CALL(bus_do_settimeofday, sbus_do_settimeofday, BTFIXUPCALL_NORM);
+	btfixup();
+
+	if (ARCH_SUN4)
+		sun4_clock_probe();
+	else
+		clock_probe();
+
+	sparc_init_timers(timer_interrupt);
+	
+#ifdef CONFIG_SUN4
+	if(idprom->id_machtype == (SM_SUN4 | SM_4_330)) {
+#endif
+	mregs = (struct mostek48t02 *)mstk48t02_regs;
+	if(!mregs) {
+		prom_printf("Something wrong, clock regs not mapped yet.\n");
+		prom_halt();
+	}		
+	spin_lock_irq(&mostek_lock);
+	mregs->creg |= MSTK_CREG_READ;
+	sec = MSTK_REG_SEC(mregs);
+	min = MSTK_REG_MIN(mregs);
+	hour = MSTK_REG_HOUR(mregs);
+	day = MSTK_REG_DOM(mregs);
+	mon = MSTK_REG_MONTH(mregs);
+	year = MSTK_CVT_YEAR( MSTK_REG_YEAR(mregs) );
+	xtime.tv_sec = mktime(year, mon, day, hour, min, sec);
+	xtime.tv_nsec = (INITIAL_JIFFIES % HZ) * (NSEC_PER_SEC / HZ);
+        set_normalized_timespec(&wall_to_monotonic,
+                                -xtime.tv_sec, -xtime.tv_nsec);
+	mregs->creg &= ~MSTK_CREG_READ;
+	spin_unlock_irq(&mostek_lock);
+#ifdef CONFIG_SUN4
+	} else if(idprom->id_machtype == (SM_SUN4 | SM_4_260) ) {
+		/* initialise the intersil on sun4 */
+
+		iregs=intersil_clock;
+		if(!iregs) {
+			prom_printf("Something wrong, clock regs not mapped yet.\n");
+			prom_halt();
+		}
+
+		intersil_intr(intersil_clock,INTERSIL_INT_100HZ);
+		disable_pil_irq(10);
+		intersil_stop(iregs);
+		intersil_read_intr(intersil_clock, temp);
+
+		temp = iregs->clk.int_csec;
+
+		sec = iregs->clk.int_sec;
+		min = iregs->clk.int_min;
+		hour = iregs->clk.int_hour;
+		day = iregs->clk.int_day;
+		mon = iregs->clk.int_month;
+		year = MSTK_CVT_YEAR(iregs->clk.int_year);
+
+		enable_pil_irq(10);
+		intersil_start(iregs);
+
+		xtime.tv_sec = mktime(year, mon, day, hour, min, sec);
+		xtime.tv_nsec = (INITIAL_JIFFIES % HZ) * (NSEC_PER_SEC / HZ);
+	        set_normalized_timespec(&wall_to_monotonic,
+ 	                               -xtime.tv_sec, -xtime.tv_nsec);
+		printk("%u/%u/%u %u:%u:%u\n",day,mon,year,hour,min,sec);
+	}
+#endif
+
+	/* Now that OBP ticker has been silenced, it is safe to enable IRQ. */
+	local_irq_enable();
+}
+
+void __init time_init(void)
+{
+#ifdef CONFIG_PCI
+	extern void pci_time_init(void);
+	if (pcic_present()) {
+		pci_time_init();
+		return;
+	}
+#endif
+	sbus_time_init();
+}
+
+extern __inline__ unsigned long do_gettimeoffset(void)
+{
+	return (*master_l10_counter >> 10) & 0x1fffff;
+}
+
+/*
+ * Returns nanoseconds
+ * XXX This is a suboptimal implementation.
+ */
+unsigned long long sched_clock(void)
+{
+	return (unsigned long long)jiffies * (1000000000 / HZ);
+}
+
+/* Ok, my cute asm atomicity trick doesn't work anymore.
+ * There are just too many variables that need to be protected
+ * now (both members of xtime, wall_jiffies, et al.)
+ */
+void do_gettimeofday(struct timeval *tv)
+{
+	unsigned long flags;
+	unsigned long seq;
+	unsigned long usec, sec;
+	unsigned long max_ntp_tick = tick_usec - tickadj;
+
+	do {
+		unsigned long lost;
+
+		seq = read_seqbegin_irqsave(&xtime_lock, flags);
+		usec = do_gettimeoffset();
+		lost = jiffies - wall_jiffies;
+
+		/*
+		 * If time_adjust is negative then NTP is slowing the clock
+		 * so make sure not to go into next possible interval.
+		 * Better to lose some accuracy than have time go backwards..
+		 */
+		if (unlikely(time_adjust < 0)) {
+			usec = min(usec, max_ntp_tick);
+
+			if (lost)
+				usec += lost * max_ntp_tick;
+		}
+		else if (unlikely(lost))
+			usec += lost * tick_usec;
+
+		sec = xtime.tv_sec;
+		usec += (xtime.tv_nsec / 1000);
+	} while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
+
+	while (usec >= 1000000) {
+		usec -= 1000000;
+		sec++;
+	}
+
+	tv->tv_sec = sec;
+	tv->tv_usec = usec;
+}
+
+EXPORT_SYMBOL(do_gettimeofday);
+
+int do_settimeofday(struct timespec *tv)
+{
+	int ret;
+
+	write_seqlock_irq(&xtime_lock);
+	ret = bus_do_settimeofday(tv);
+	write_sequnlock_irq(&xtime_lock);
+	clock_was_set();
+	return ret;
+}
+
+EXPORT_SYMBOL(do_settimeofday);
+
+static int sbus_do_settimeofday(struct timespec *tv)
+{
+	time_t wtm_sec, sec = tv->tv_sec;
+	long wtm_nsec, nsec = tv->tv_nsec;
+
+	if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
+		return -EINVAL;
+
+	/*
+	 * This is revolting. We need to set "xtime" correctly. However, the
+	 * value in this location is the value at the most recent update of
+	 * wall time.  Discover what correction gettimeofday() would have
+	 * made, and then undo it!
+	 */
+	nsec -= 1000 * (do_gettimeoffset() +
+			(jiffies - wall_jiffies) * (USEC_PER_SEC / HZ));
+
+	wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
+	wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
+
+	set_normalized_timespec(&xtime, sec, nsec);
+	set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
+
+	time_adjust = 0;		/* stop active adjtime() */
+	time_status |= STA_UNSYNC;
+	time_maxerror = NTP_PHASE_LIMIT;
+	time_esterror = NTP_PHASE_LIMIT;
+	return 0;
+}
+
+/*
+ * BUG: This routine does not handle hour overflow properly; it just
+ *      sets the minutes. Usually you won't notice until after reboot!
+ */
+static int set_rtc_mmss(unsigned long nowtime)
+{
+	int real_seconds, real_minutes, mostek_minutes;
+	struct mostek48t02 *regs = (struct mostek48t02 *)mstk48t02_regs;
+	unsigned long flags;
+#ifdef CONFIG_SUN4
+	struct intersil *iregs = intersil_clock;
+	int temp;
+#endif
+
+	/* Not having a register set can lead to trouble. */
+	if (!regs) {
+#ifdef CONFIG_SUN4
+		if(!iregs)
+		return -1;
+	 	else {
+			temp = iregs->clk.int_csec;
+
+			mostek_minutes = iregs->clk.int_min;
+
+			real_seconds = nowtime % 60;
+			real_minutes = nowtime / 60;
+			if (((abs(real_minutes - mostek_minutes) + 15)/30) & 1)
+				real_minutes += 30;	/* correct for half hour time zone */
+			real_minutes %= 60;
+
+			if (abs(real_minutes - mostek_minutes) < 30) {
+				intersil_stop(iregs);
+				iregs->clk.int_sec=real_seconds;
+				iregs->clk.int_min=real_minutes;
+				intersil_start(iregs);
+			} else {
+				printk(KERN_WARNING
+			       "set_rtc_mmss: can't update from %d to %d\n",
+				       mostek_minutes, real_minutes);
+				return -1;
+			}
+			
+			return 0;
+		}
+#endif
+	}
+
+	spin_lock_irqsave(&mostek_lock, flags);
+	/* Read the current RTC minutes. */
+	regs->creg |= MSTK_CREG_READ;
+	mostek_minutes = MSTK_REG_MIN(regs);
+	regs->creg &= ~MSTK_CREG_READ;
+
+	/*
+	 * since we're only adjusting minutes and seconds,
+	 * don't interfere with hour overflow. This avoids
+	 * messing with unknown time zones but requires your
+	 * RTC not to be off by more than 15 minutes
+	 */
+	real_seconds = nowtime % 60;
+	real_minutes = nowtime / 60;
+	if (((abs(real_minutes - mostek_minutes) + 15)/30) & 1)
+		real_minutes += 30;	/* correct for half hour time zone */
+	real_minutes %= 60;
+
+	if (abs(real_minutes - mostek_minutes) < 30) {
+		regs->creg |= MSTK_CREG_WRITE;
+		MSTK_SET_REG_SEC(regs,real_seconds);
+		MSTK_SET_REG_MIN(regs,real_minutes);
+		regs->creg &= ~MSTK_CREG_WRITE;
+		spin_unlock_irqrestore(&mostek_lock, flags);
+		return 0;
+	} else {
+		spin_unlock_irqrestore(&mostek_lock, flags);
+		return -1;
+	}
+}