arch/sparc/kernel/time.c

   1 /* $Id: time.c,v 1.60 2002/01/23 14:33:55 davem Exp $
   2  * linux/arch/sparc/kernel/time.c
   3  *
   4  * Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
   5  * Copyright (C) 1996 Thomas K. Dyas (tdyas@eden.rutgers.edu)
   6  *
   7  * Chris Davis (cdavis@cois.on.ca) 03/27/1998
   8  * Added support for the intersil on the sun4/4200
   9  *
  10  * Gleb Raiko (rajko@mech.math.msu.su) 08/18/1998
  11  * Support for MicroSPARC-IIep, PCI CPU.
  12  *
  13  * This file handles the Sparc specific time handling details.
  14  *
  15  * 1997-09-10   Updated NTP code according to technical memorandum Jan '96
  16  *              "A Kernel Model for Precision Timekeeping" by Dave Mills
  17  */
  18 #include <linux/config.h>
  19 #include <linux/errno.h>
  20 #include <linux/module.h>
  21 #include <linux/sched.h>
  22 #include <linux/kernel.h>
  23 #include <linux/param.h>
  24 #include <linux/string.h>
  25 #include <linux/mm.h>
  26 #include <linux/interrupt.h>
  27 #include <linux/time.h>
  28 #include <linux/timex.h>
  29 #include <linux/init.h>
  30 #include <linux/pci.h>
  31 #include <linux/ioport.h>
  32 #include <linux/profile.h>
  33
  34 #include <asm/oplib.h>
  35 #include <asm/timer.h>
  36 #include <asm/mostek.h>
  37 #include <asm/system.h>
  38 #include <asm/irq.h>
  39 #include <asm/io.h>
  40 #include <asm/idprom.h>
  41 #include <asm/machines.h>
  42 #include <asm/sun4paddr.h>
  43 #include <asm/page.h>
  44 #include <asm/pcic.h>
  45
  46 extern unsigned long wall_jiffies;
  47
  48 u64 jiffies_64 = INITIAL_JIFFIES;
  49
  50 EXPORT_SYMBOL(jiffies_64);
  51
  52 DEFINE_SPINLOCK(rtc_lock);
  53 enum sparc_clock_type sp_clock_typ;
  54 DEFINE_SPINLOCK(mostek_lock);
  55 void __iomem *mstk48t02_regs = NULL;
  56 static struct mostek48t08 *mstk48t08_regs = NULL;
  57 static int set_rtc_mmss(unsigned long);
  58 static int sbus_do_settimeofday(struct timespec *tv);
  59
  60 #ifdef CONFIG_SUN4
  61 struct intersil *intersil_clock;
  62 #define intersil_cmd(intersil_reg, intsil_cmd) intersil_reg->int_cmd_reg = \
  63         (intsil_cmd)
  64
  65 #define intersil_intr(intersil_reg, intsil_cmd) intersil_reg->int_intr_reg = \
  66         (intsil_cmd)
  67
  68 #define intersil_start(intersil_reg) intersil_cmd(intersil_reg, \
  69         ( INTERSIL_START | INTERSIL_32K | INTERSIL_NORMAL | INTERSIL_24H |\
  70           INTERSIL_INTR_ENABLE))
  71
  72 #define intersil_stop(intersil_reg) intersil_cmd(intersil_reg, \
  73         ( INTERSIL_STOP | INTERSIL_32K | INTERSIL_NORMAL | INTERSIL_24H |\
  74           INTERSIL_INTR_ENABLE))
  75
  76 #define intersil_read_intr(intersil_reg, towhere) towhere = \
  77         intersil_reg->int_intr_reg
  78
  79 #endif
  80
  81 unsigned long profile_pc(struct pt_regs *regs)
  82 {
  83         extern char __copy_user_begin[], __copy_user_end[];
  84         extern char __atomic_begin[], __atomic_end[];
  85         extern char __bzero_begin[], __bzero_end[];
  86         extern char __bitops_begin[], __bitops_end[];
  87
  88         unsigned long pc = regs->pc;
  89
  90         if (in_lock_functions(pc) ||
  91             (pc >= (unsigned long) __copy_user_begin &&
  92              pc < (unsigned long) __copy_user_end) ||
  93             (pc >= (unsigned long) __atomic_begin &&
  94              pc < (unsigned long) __atomic_end) ||
  95             (pc >= (unsigned long) __bzero_begin &&
  96              pc < (unsigned long) __bzero_end) ||
  97             (pc >= (unsigned long) __bitops_begin &&
  98              pc < (unsigned long) __bitops_end))
  99                 pc = regs->u_regs[UREG_RETPC];
 100         return pc;
 101 }
 102
 103 __volatile__ unsigned int *master_l10_counter;
 104 __volatile__ unsigned int *master_l10_limit;
 105
 106 /*
 107  * timer_interrupt() needs to keep up the real-time clock,
 108  * as well as call the "do_timer()" routine every clocktick
 109  */
 110
 111 #define TICK_SIZE (tick_nsec / 1000)
 112
 113 irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs * regs)
 114 {
 115         /* last time the cmos clock got updated */
 116         static long last_rtc_update;
 117
 118 #ifndef CONFIG_SMP
 119         profile_tick(CPU_PROFILING, regs);
 120 #endif
 121
 122         /* Protect counter clear so that do_gettimeoffset works */
 123         write_seqlock(&xtime_lock);
 124 #ifdef CONFIG_SUN4
 125         if((idprom->id_machtype == (SM_SUN4 | SM_4_260)) ||
 126            (idprom->id_machtype == (SM_SUN4 | SM_4_110))) {
 127                 int temp;
 128                 intersil_read_intr(intersil_clock, temp);
 129                 /* re-enable the irq */
 130                 enable_pil_irq(10);
 131         }
 132 #endif
 133         clear_clock_irq();
 134
 135         do_timer(regs);
 136 #ifndef CONFIG_SMP
 137         update_process_times(user_mode(regs));
 138 #endif
 139
 140
 141         /* Determine when to update the Mostek clock. */
 142         if ((time_status & STA_UNSYNC) == 0 &&
 143             xtime.tv_sec > last_rtc_update + 660 &&
 144             (xtime.tv_nsec / 1000) >= 500000 - ((unsigned) TICK_SIZE) / 2 &&
 145             (xtime.tv_nsec / 1000) <= 500000 + ((unsigned) TICK_SIZE) / 2) {
 146           if (set_rtc_mmss(xtime.tv_sec) == 0)
 147             last_rtc_update = xtime.tv_sec;
 148           else
 149             last_rtc_update = xtime.tv_sec - 600; /* do it again in 60 s */
 150         }
 151         write_sequnlock(&xtime_lock);
 152
 153         return IRQ_HANDLED;
 154 }
 155
 156 /* Kick start a stopped clock (procedure from the Sun NVRAM/hostid FAQ). */
 157 static void __init kick_start_clock(void)
 158 {
 159         struct mostek48t02 *regs = (struct mostek48t02 *)mstk48t02_regs;
 160         unsigned char sec;
 161         int i, count;
 162
 163         prom_printf("CLOCK: Clock was stopped. Kick start ");
 164
 165         spin_lock_irq(&mostek_lock);
 166
 167         /* Turn on the kick start bit to start the oscillator. */
 168         regs->creg |= MSTK_CREG_WRITE;
 169         regs->sec &= ~MSTK_STOP;
 170         regs->hour |= MSTK_KICK_START;
 171         regs->creg &= ~MSTK_CREG_WRITE;
 172
 173         spin_unlock_irq(&mostek_lock);
 174
 175         /* Delay to allow the clock oscillator to start. */
 176         sec = MSTK_REG_SEC(regs);
 177         for (i = 0; i < 3; i++) {
 178                 while (sec == MSTK_REG_SEC(regs))
 179                         for (count = 0; count < 100000; count++)
 180                                 /* nothing */ ;
 181                 prom_printf(".");
 182                 sec = regs->sec;
 183         }
 184         prom_printf("\n");
 185
 186         spin_lock_irq(&mostek_lock);
 187
 188         /* Turn off kick start and set a "valid" time and date. */
 189         regs->creg |= MSTK_CREG_WRITE;
 190         regs->hour &= ~MSTK_KICK_START;
 191         MSTK_SET_REG_SEC(regs,0);
 192         MSTK_SET_REG_MIN(regs,0);
 193         MSTK_SET_REG_HOUR(regs,0);
 194         MSTK_SET_REG_DOW(regs,5);
 195         MSTK_SET_REG_DOM(regs,1);
 196         MSTK_SET_REG_MONTH(regs,8);
 197         MSTK_SET_REG_YEAR(regs,1996 - MSTK_YEAR_ZERO);
 198         regs->creg &= ~MSTK_CREG_WRITE;
 199
 200         spin_unlock_irq(&mostek_lock);
 201
 202         /* Ensure the kick start bit is off. If it isn't, turn it off. */
 203         while (regs->hour & MSTK_KICK_START) {
 204                 prom_printf("CLOCK: Kick start still on!\n");
 205
 206                 spin_lock_irq(&mostek_lock);
 207                 regs->creg |= MSTK_CREG_WRITE;
 208                 regs->hour &= ~MSTK_KICK_START;
 209                 regs->creg &= ~MSTK_CREG_WRITE;
 210                 spin_unlock_irq(&mostek_lock);
 211         }
 212
 213         prom_printf("CLOCK: Kick start procedure successful.\n");
 214 }
 215
 216 /* Return nonzero if the clock chip battery is low. */
 217 static __inline__ int has_low_battery(void)
 218 {
 219         struct mostek48t02 *regs = (struct mostek48t02 *)mstk48t02_regs;
 220         unsigned char data1, data2;
 221
 222         spin_lock_irq(&mostek_lock);
 223         data1 = regs->eeprom[0];        /* Read some data. */
 224         regs->eeprom[0] = ~data1;       /* Write back the complement. */
 225         data2 = regs->eeprom[0];        /* Read back the complement. */
 226         regs->eeprom[0] = data1;        /* Restore the original value. */
 227         spin_unlock_irq(&mostek_lock);
 228
 229         return (data1 == data2);        /* Was the write blocked? */
 230 }
 231
 232 /* Probe for the real time clock chip on Sun4 */
 233 static __inline__ void sun4_clock_probe(void)
 234 {
 235 #ifdef CONFIG_SUN4
 236         int temp;
 237         struct resource r;
 238
 239         memset(&r, 0, sizeof(r));
 240         if( idprom->id_machtype == (SM_SUN4 | SM_4_330) ) {
 241                 sp_clock_typ = MSTK48T02;
 242                 r.start = sun4_clock_physaddr;
 243                 mstk48t02_regs = sbus_ioremap(&r, 0,
 244                                        sizeof(struct mostek48t02), NULL);
 245                 mstk48t08_regs = NULL;  /* To catch weirdness */
 246                 intersil_clock = NULL;  /* just in case */
 247
 248                 /* Kick start the clock if it is completely stopped. */
 249                 if (mostek_read(mstk48t02_regs + MOSTEK_SEC) & MSTK_STOP)
 250                         kick_start_clock();
 251         } else if( idprom->id_machtype == (SM_SUN4 | SM_4_260)) {
 252                 /* intersil setup code */
 253                 printk("Clock: INTERSIL at %8x ",sun4_clock_physaddr);
 254                 sp_clock_typ = INTERSIL;
 255                 r.start = sun4_clock_physaddr;
 256                 intersil_clock = (struct intersil *)
 257                     sbus_ioremap(&r, 0, sizeof(*intersil_clock), "intersil");
 258                 mstk48t02_regs = 0;  /* just be sure */
 259                 mstk48t08_regs = NULL;  /* ditto */
 260                 /* initialise the clock */
 261
 262                 intersil_intr(intersil_clock,INTERSIL_INT_100HZ);
 263
 264                 intersil_start(intersil_clock);
 265
 266                 intersil_read_intr(intersil_clock, temp);
 267                 while (!(temp & 0x80))
 268                         intersil_read_intr(intersil_clock, temp);
 269
 270                 intersil_read_intr(intersil_clock, temp);
 271                 while (!(temp & 0x80))
 272                         intersil_read_intr(intersil_clock, temp);
 273
 274                 intersil_stop(intersil_clock);
 275
 276         }
 277 #endif
 278 }
 279
 280 /* Probe for the mostek real time clock chip. */
 281 static __inline__ void clock_probe(void)
 282 {
 283         struct linux_prom_registers clk_reg[2];
 284         char model[128];
 285         register int node, cpuunit, bootbus;
 286         struct resource r;
 287
 288         cpuunit = bootbus = 0;
 289         memset(&r, 0, sizeof(r));
 290
 291         /* Determine the correct starting PROM node for the probe. */
 292         node = prom_getchild(prom_root_node);
 293         switch (sparc_cpu_model) {
 294         case sun4c:
 295                 break;
 296         case sun4m:
 297                 node = prom_getchild(prom_searchsiblings(node, "obio"));
 298                 break;
 299         case sun4d:
 300                 node = prom_getchild(bootbus = prom_searchsiblings(prom_getchild(cpuunit = prom_searchsiblings(node, "cpu-unit")), "bootbus"));
 301                 break;
 302         default:
 303                 prom_printf("CLOCK: Unsupported architecture!\n");
 304                 prom_halt();
 305         }
 306
 307         /* Find the PROM node describing the real time clock. */
 308         sp_clock_typ = MSTK_INVALID;
 309         node = prom_searchsiblings(node,"eeprom");
 310         if (!node) {
 311                 prom_printf("CLOCK: No clock found!\n");
 312                 prom_halt();
 313         }
 314
 315         /* Get the model name and setup everything up. */
 316         model[0] = '\0';
 317         prom_getstring(node, "model", model, sizeof(model));
 318         if (strcmp(model, "mk48t02") == 0) {
 319                 sp_clock_typ = MSTK48T02;
 320                 if (prom_getproperty(node, "reg", (char *) clk_reg, sizeof(clk_reg)) == -1) {
 321                         prom_printf("clock_probe: FAILED!\n");
 322                         prom_halt();
 323                 }
 324                 if (sparc_cpu_model == sun4d)
 325                         prom_apply_generic_ranges (bootbus, cpuunit, clk_reg, 1);
 326                 else
 327                         prom_apply_obio_ranges(clk_reg, 1);
 328                 /* Map the clock register io area read-only */
 329                 r.flags = clk_reg[0].which_io;
 330                 r.start = clk_reg[0].phys_addr;
 331                 mstk48t02_regs = sbus_ioremap(&r, 0,
 332                     sizeof(struct mostek48t02), "mk48t02");
 333                 mstk48t08_regs = NULL;  /* To catch weirdness */
 334         } else if (strcmp(model, "mk48t08") == 0) {
 335                 sp_clock_typ = MSTK48T08;
 336                 if(prom_getproperty(node, "reg", (char *) clk_reg,
 337                                     sizeof(clk_reg)) == -1) {
 338                         prom_printf("clock_probe: FAILED!\n");
 339                         prom_halt();
 340                 }
 341                 if (sparc_cpu_model == sun4d)
 342                         prom_apply_generic_ranges (bootbus, cpuunit, clk_reg, 1);
 343                 else
 344                         prom_apply_obio_ranges(clk_reg, 1);
 345                 /* Map the clock register io area read-only */
 346                 /* XXX r/o attribute is somewhere in r.flags */
 347                 r.flags = clk_reg[0].which_io;
 348                 r.start = clk_reg[0].phys_addr;
 349                 mstk48t08_regs = (struct mostek48t08 *) sbus_ioremap(&r, 0,
 350                     sizeof(struct mostek48t08), "mk48t08");
 351
 352                 mstk48t02_regs = &mstk48t08_regs->regs;
 353         } else {
 354                 prom_printf("CLOCK: Unknown model name '%s'\n",model);
 355                 prom_halt();
 356         }
 357
 358         /* Report a low battery voltage condition. */
 359         if (has_low_battery())
 360                 printk(KERN_CRIT "NVRAM: Low battery voltage!\n");
 361
 362         /* Kick start the clock if it is completely stopped. */
 363         if (mostek_read(mstk48t02_regs + MOSTEK_SEC) & MSTK_STOP)
 364                 kick_start_clock();
 365 }
 366
 367 void __init sbus_time_init(void)
 368 {
 369         unsigned int year, mon, day, hour, min, sec;
 370         struct mostek48t02 *mregs;
 371
 372 #ifdef CONFIG_SUN4
 373         int temp;
 374         struct intersil *iregs;
 375 #endif
 376
 377         BTFIXUPSET_CALL(bus_do_settimeofday, sbus_do_settimeofday, BTFIXUPCALL_NORM);
 378         btfixup();
 379
 380         if (ARCH_SUN4)
 381                 sun4_clock_probe();
 382         else
 383                 clock_probe();
 384
 385         sparc_init_timers(timer_interrupt);
 386
 387 #ifdef CONFIG_SUN4
 388         if(idprom->id_machtype == (SM_SUN4 | SM_4_330)) {
 389 #endif
 390         mregs = (struct mostek48t02 *)mstk48t02_regs;
 391         if(!mregs) {
 392                 prom_printf("Something wrong, clock regs not mapped yet.\n");
 393                 prom_halt();
 394         }
 395         spin_lock_irq(&mostek_lock);
 396         mregs->creg |= MSTK_CREG_READ;
 397         sec = MSTK_REG_SEC(mregs);
 398         min = MSTK_REG_MIN(mregs);
 399         hour = MSTK_REG_HOUR(mregs);
 400         day = MSTK_REG_DOM(mregs);
 401         mon = MSTK_REG_MONTH(mregs);
 402         year = MSTK_CVT_YEAR( MSTK_REG_YEAR(mregs) );
 403         xtime.tv_sec = mktime(year, mon, day, hour, min, sec);
 404         xtime.tv_nsec = (INITIAL_JIFFIES % HZ) * (NSEC_PER_SEC / HZ);
 405         set_normalized_timespec(&wall_to_monotonic,
 406                                 -xtime.tv_sec, -xtime.tv_nsec);
 407         mregs->creg &= ~MSTK_CREG_READ;
 408         spin_unlock_irq(&mostek_lock);
 409 #ifdef CONFIG_SUN4
 410         } else if(idprom->id_machtype == (SM_SUN4 | SM_4_260) ) {
 411                 /* initialise the intersil on sun4 */
 412
 413                 iregs=intersil_clock;
 414                 if(!iregs) {
 415                         prom_printf("Something wrong, clock regs not mapped yet.\n");
 416                         prom_halt();
 417                 }
 418
 419                 intersil_intr(intersil_clock,INTERSIL_INT_100HZ);
 420                 disable_pil_irq(10);
 421                 intersil_stop(iregs);
 422                 intersil_read_intr(intersil_clock, temp);
 423
 424                 temp = iregs->clk.int_csec;
 425
 426                 sec = iregs->clk.int_sec;
 427                 min = iregs->clk.int_min;
 428                 hour = iregs->clk.int_hour;
 429                 day = iregs->clk.int_day;
 430                 mon = iregs->clk.int_month;
 431                 year = MSTK_CVT_YEAR(iregs->clk.int_year);
 432
 433                 enable_pil_irq(10);
 434                 intersil_start(iregs);
 435
 436                 xtime.tv_sec = mktime(year, mon, day, hour, min, sec);
 437                 xtime.tv_nsec = (INITIAL_JIFFIES % HZ) * (NSEC_PER_SEC / HZ);
 438                 set_normalized_timespec(&wall_to_monotonic,
 439                                        -xtime.tv_sec, -xtime.tv_nsec);
 440                 printk("%u/%u/%u %u:%u:%u\n",day,mon,year,hour,min,sec);
 441         }
 442 #endif
 443
 444         /* Now that OBP ticker has been silenced, it is safe to enable IRQ. */
 445         local_irq_enable();
 446 }
 447
 448 void __init time_init(void)
 449 {
 450 #ifdef CONFIG_PCI
 451         extern void pci_time_init(void);
 452         if (pcic_present()) {
 453                 pci_time_init();
 454                 return;
 455         }
 456 #endif
 457         sbus_time_init();
 458 }
 459
 460 extern __inline__ unsigned long do_gettimeoffset(void)
 461 {
 462         return (*master_l10_counter >> 10) & 0x1fffff;
 463 }
 464
 465 /*
 466  * Returns nanoseconds
 467  * XXX This is a suboptimal implementation.
 468  */
 469 unsigned long long sched_clock(void)
 470 {
 471         return (unsigned long long)jiffies * (1000000000 / HZ);
 472 }
 473
 474 /* Ok, my cute asm atomicity trick doesn't work anymore.
 475  * There are just too many variables that need to be protected
 476  * now (both members of xtime, wall_jiffies, et al.)
 477  */
 478 void do_gettimeofday(struct timeval *tv)
 479 {
 480         unsigned long flags;
 481         unsigned long seq;
 482         unsigned long usec, sec;
 483         unsigned long max_ntp_tick = tick_usec - tickadj;
 484
 485         do {
 486                 unsigned long lost;
 487
 488                 seq = read_seqbegin_irqsave(&xtime_lock, flags);
 489                 usec = do_gettimeoffset();
 490                 lost = jiffies - wall_jiffies;
 491
 492                 /*
 493                  * If time_adjust is negative then NTP is slowing the clock
 494                  * so make sure not to go into next possible interval.
 495                  * Better to lose some accuracy than have time go backwards..
 496                  */
 497                 if (unlikely(time_adjust < 0)) {
 498                         usec = min(usec, max_ntp_tick);
 499
 500                         if (lost)
 501                                 usec += lost * max_ntp_tick;
 502                 }
 503                 else if (unlikely(lost))
 504                         usec += lost * tick_usec;
 505
 506                 sec = xtime.tv_sec;
 507                 usec += (xtime.tv_nsec / 1000);
 508         } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
 509
 510         while (usec >= 1000000) {
 511                 usec -= 1000000;
 512                 sec++;
 513         }
 514
 515         tv->tv_sec = sec;
 516         tv->tv_usec = usec;
 517 }
 518
 519 EXPORT_SYMBOL(do_gettimeofday);
 520
 521 int do_settimeofday(struct timespec *tv)
 522 {
 523         int ret;
 524
 525         write_seqlock_irq(&xtime_lock);
 526         ret = bus_do_settimeofday(tv);
 527         write_sequnlock_irq(&xtime_lock);
 528         clock_was_set();
 529         return ret;
 530 }
 531
 532 EXPORT_SYMBOL(do_settimeofday);
 533
 534 static int sbus_do_settimeofday(struct timespec *tv)
 535 {
 536         time_t wtm_sec, sec = tv->tv_sec;
 537         long wtm_nsec, nsec = tv->tv_nsec;
 538
 539         if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
 540                 return -EINVAL;
 541
 542         /*
 543          * This is revolting. We need to set "xtime" correctly. However, the
 544          * value in this location is the value at the most recent update of
 545          * wall time.  Discover what correction gettimeofday() would have
 546          * made, and then undo it!
 547          */
 548         nsec -= 1000 * (do_gettimeoffset() +
 549                         (jiffies - wall_jiffies) * (USEC_PER_SEC / HZ));
 550
 551         wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
 552         wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
 553
 554         set_normalized_timespec(&xtime, sec, nsec);
 555         set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
 556
 557         time_adjust = 0;                /* stop active adjtime() */
 558         time_status |= STA_UNSYNC;
 559         time_maxerror = NTP_PHASE_LIMIT;
 560         time_esterror = NTP_PHASE_LIMIT;
 561         return 0;
 562 }
 563
 564 /*
 565  * BUG: This routine does not handle hour overflow properly; it just
 566  *      sets the minutes. Usually you won't notice until after reboot!
 567  */
 568 static int set_rtc_mmss(unsigned long nowtime)
 569 {
 570         int real_seconds, real_minutes, mostek_minutes;
 571         struct mostek48t02 *regs = (struct mostek48t02 *)mstk48t02_regs;
 572         unsigned long flags;
 573 #ifdef CONFIG_SUN4
 574         struct intersil *iregs = intersil_clock;
 575         int temp;
 576 #endif
 577
 578         /* Not having a register set can lead to trouble. */
 579         if (!regs) {
 580 #ifdef CONFIG_SUN4
 581                 if(!iregs)
 582                 return -1;
 583                 else {
 584                         temp = iregs->clk.int_csec;
 585
 586                         mostek_minutes = iregs->clk.int_min;
 587
 588                         real_seconds = nowtime % 60;
 589                         real_minutes = nowtime / 60;
 590                         if (((abs(real_minutes - mostek_minutes) + 15)/30) & 1)
 591                                 real_minutes += 30;     /* correct for half hour time zone */
 592                         real_minutes %= 60;
 593
 594                         if (abs(real_minutes - mostek_minutes) < 30) {
 595                                 intersil_stop(iregs);
 596                                 iregs->clk.int_sec=real_seconds;
 597                                 iregs->clk.int_min=real_minutes;
 598                                 intersil_start(iregs);
 599                         } else {
 600                                 printk(KERN_WARNING
 601                                "set_rtc_mmss: can't update from %d to %d\n",
 602                                        mostek_minutes, real_minutes);
 603                                 return -1;
 604                         }
 605
 606                         return 0;
 607                 }
 608 #endif
 609         }
 610
 611         spin_lock_irqsave(&mostek_lock, flags);
 612         /* Read the current RTC minutes. */
 613         regs->creg |= MSTK_CREG_READ;
 614         mostek_minutes = MSTK_REG_MIN(regs);
 615         regs->creg &= ~MSTK_CREG_READ;
 616
 617         /*
 618          * since we're only adjusting minutes and seconds,
 619          * don't interfere with hour overflow. This avoids
 620          * messing with unknown time zones but requires your
 621          * RTC not to be off by more than 15 minutes
 622          */
 623         real_seconds = nowtime % 60;
 624         real_minutes = nowtime / 60;
 625         if (((abs(real_minutes - mostek_minutes) + 15)/30) & 1)
 626                 real_minutes += 30;     /* correct for half hour time zone */
 627         real_minutes %= 60;
 628
 629         if (abs(real_minutes - mostek_minutes) < 30) {
 630                 regs->creg |= MSTK_CREG_WRITE;
 631                 MSTK_SET_REG_SEC(regs,real_seconds);
 632                 MSTK_SET_REG_MIN(regs,real_minutes);
 633                 regs->creg &= ~MSTK_CREG_WRITE;
 634                 spin_unlock_irqrestore(&mostek_lock, flags);
 635                 return 0;
 636         } else {
 637                 spin_unlock_irqrestore(&mostek_lock, flags);
 638                 return -1;
 639         }
 640 }