Linux-2.6.12-rc2v2.6.12-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;
+        }
+}