arch/parisc/kernel/time.c

   1 /*
   2  *  linux/arch/parisc/kernel/time.c
   3  *
   4  *  Copyright (C) 1991, 1992, 1995  Linus Torvalds
   5  *  Modifications for ARM (C) 1994, 1995, 1996,1997 Russell King
   6  *  Copyright (C) 1999 SuSE GmbH, (Philipp Rumpf, prumpf@tux.org)
   7  *
   8  * 1994-07-02  Alan Modra
   9  *             fixed set_rtc_mmss, fixed time.year for >= 2000, new mktime
  10  * 1998-12-20  Updated NTP code according to technical memorandum Jan '96
  11  *             "A Kernel Model for Precision Timekeeping" by Dave Mills
  12  */
  13 #include <linux/errno.h>
  14 #include <linux/module.h>
  15 #include <linux/sched.h>
  16 #include <linux/kernel.h>
  17 #include <linux/param.h>
  18 #include <linux/string.h>
  19 #include <linux/mm.h>
  20 #include <linux/interrupt.h>
  21 #include <linux/time.h>
  22 #include <linux/init.h>
  23 #include <linux/smp.h>
  24 #include <linux/profile.h>
  25
  26 #include <asm/uaccess.h>
  27 #include <asm/io.h>
  28 #include <asm/irq.h>
  29 #include <asm/param.h>
  30 #include <asm/pdc.h>
  31 #include <asm/led.h>
  32
  33 #include <linux/timex.h>
  34
  35 static unsigned long clocktick __read_mostly;   /* timer cycles per tick */
  36
  37 /*
  38  * We keep time on PA-RISC Linux by using the Interval Timer which is
  39  * a pair of registers; one is read-only and one is write-only; both
  40  * accessed through CR16.  The read-only register is 32 or 64 bits wide,
  41  * and increments by 1 every CPU clock tick.  The architecture only
  42  * guarantees us a rate between 0.5 and 2, but all implementations use a
  43  * rate of 1.  The write-only register is 32-bits wide.  When the lowest
  44  * 32 bits of the read-only register compare equal to the write-only
  45  * register, it raises a maskable external interrupt.  Each processor has
  46  * an Interval Timer of its own and they are not synchronised.
  47  *
  48  * We want to generate an interrupt every 1/HZ seconds.  So we program
  49  * CR16 to interrupt every @clocktick cycles.  The it_value in cpu_data
  50  * is programmed with the intended time of the next tick.  We can be
  51  * held off for an arbitrarily long period of time by interrupts being
  52  * disabled, so we may miss one or more ticks.
  53  */
  54 irqreturn_t timer_interrupt(int irq, void *dev_id)
  55 {
  56         unsigned long now;
  57         unsigned long next_tick;
  58         unsigned long cycles_elapsed, ticks_elapsed;
  59         unsigned long cycles_remainder;
  60         unsigned int cpu = smp_processor_id();
  61         struct cpuinfo_parisc *cpuinfo = &cpu_data[cpu];
  62
  63         /* gcc can optimize for "read-only" case with a local clocktick */
  64         unsigned long cpt = clocktick;
  65
  66         profile_tick(CPU_PROFILING);
  67
  68         /* Initialize next_tick to the expected tick time. */
  69         next_tick = cpuinfo->it_value;
  70
  71         /* Get current interval timer.
  72          * CR16 reads as 64 bits in CPU wide mode.
  73          * CR16 reads as 32 bits in CPU narrow mode.
  74          */
  75         now = mfctl(16);
  76
  77         cycles_elapsed = now - next_tick;
  78
  79         if ((cycles_elapsed >> 5) < cpt) {
  80                 /* use "cheap" math (add/subtract) instead
  81                  * of the more expensive div/mul method
  82                  */
  83                 cycles_remainder = cycles_elapsed;
  84                 ticks_elapsed = 1;
  85                 while (cycles_remainder > cpt) {
  86                         cycles_remainder -= cpt;
  87                         ticks_elapsed++;
  88                 }
  89         } else {
  90                 cycles_remainder = cycles_elapsed % cpt;
  91                 ticks_elapsed = 1 + cycles_elapsed / cpt;
  92         }
  93
  94         /* Can we differentiate between "early CR16" (aka Scenario 1) and
  95          * "long delay" (aka Scenario 3)? I don't think so.
  96          *
  97          * We expected timer_interrupt to be delivered at least a few hundred
  98          * cycles after the IT fires. But it's arbitrary how much time passes
  99          * before we call it "late". I've picked one second.
 100          */
 101         if (ticks_elapsed > HZ) {
 102                 /* Scenario 3: very long delay?  bad in any case */
 103                 printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
 104                         " cycles %lX rem %lX "
 105                         " next/now %lX/%lX\n",
 106                         cpu,
 107                         cycles_elapsed, cycles_remainder,
 108                         next_tick, now );
 109         }
 110
 111         /* convert from "division remainder" to "remainder of clock tick" */
 112         cycles_remainder = cpt - cycles_remainder;
 113
 114         /* Determine when (in CR16 cycles) next IT interrupt will fire.
 115          * We want IT to fire modulo clocktick even if we miss/skip some.
 116          * But those interrupts don't in fact get delivered that regularly.
 117          */
 118         next_tick = now + cycles_remainder;
 119
 120         cpuinfo->it_value = next_tick;
 121
 122         /* Skip one clocktick on purpose if we are likely to miss next_tick.
 123          * We want to avoid the new next_tick being less than CR16.
 124          * If that happened, itimer wouldn't fire until CR16 wrapped.
 125          * We'll catch the tick we missed on the tick after that.
 126          */
 127         if (!(cycles_remainder >> 13))
 128                 next_tick += cpt;
 129
 130         /* Program the IT when to deliver the next interrupt. */
 131         /* Only bottom 32-bits of next_tick are written to cr16.  */
 132         mtctl(next_tick, 16);
 133
 134
 135         /* Done mucking with unreliable delivery of interrupts.
 136          * Go do system house keeping.
 137          */
 138
 139         if (!--cpuinfo->prof_counter) {
 140                 cpuinfo->prof_counter = cpuinfo->prof_multiplier;
 141                 update_process_times(user_mode(get_irq_regs()));
 142         }
 143
 144         if (cpu == 0) {
 145                 write_seqlock(&xtime_lock);
 146                 do_timer(ticks_elapsed);
 147                 write_sequnlock(&xtime_lock);
 148         }
 149
 150         /* check soft power switch status */
 151         if (cpu == 0 && !atomic_read(&power_tasklet.count))
 152                 tasklet_schedule(&power_tasklet);
 153
 154         return IRQ_HANDLED;
 155 }
 156
 157
 158 unsigned long profile_pc(struct pt_regs *regs)
 159 {
 160         unsigned long pc = instruction_pointer(regs);
 161
 162         if (regs->gr[0] & PSW_N)
 163                 pc -= 4;
 164
 165 #ifdef CONFIG_SMP
 166         if (in_lock_functions(pc))
 167                 pc = regs->gr[2];
 168 #endif
 169
 170         return pc;
 171 }
 172 EXPORT_SYMBOL(profile_pc);
 173
 174
 175 /*
 176  * Return the number of micro-seconds that elapsed since the last
 177  * update to wall time (aka xtime).  The xtime_lock
 178  * must be at least read-locked when calling this routine.
 179  */
 180 static inline unsigned long gettimeoffset (void)
 181 {
 182 #ifndef CONFIG_SMP
 183         /*
 184          * FIXME: This won't work on smp because jiffies are updated by cpu 0.
 185          *    Once parisc-linux learns the cr16 difference between processors,
 186          *    this could be made to work.
 187          */
 188         unsigned long now;
 189         unsigned long prev_tick;
 190         unsigned long next_tick;
 191         unsigned long elapsed_cycles;
 192         unsigned long usec;
 193         unsigned long cpuid = smp_processor_id();
 194         unsigned long cpt = clocktick;
 195
 196         next_tick = cpu_data[cpuid].it_value;
 197         now = mfctl(16);        /* Read the hardware interval timer.  */
 198
 199         prev_tick = next_tick - cpt;
 200
 201         /* Assume Scenario 1: "now" is later than prev_tick.  */
 202         elapsed_cycles = now - prev_tick;
 203
 204 /* aproximate HZ with shifts. Intended math is "(elapsed/clocktick) > HZ" */
 205 #if HZ == 1000
 206         if (elapsed_cycles > (cpt << 10) )
 207 #elif HZ == 250
 208         if (elapsed_cycles > (cpt << 8) )
 209 #elif HZ == 100
 210         if (elapsed_cycles > (cpt << 7) )
 211 #else
 212 #warn WTF is HZ set to anyway?
 213         if (elapsed_cycles > (HZ * cpt) )
 214 #endif
 215         {
 216                 /* Scenario 3: clock ticks are missing. */
 217                 printk (KERN_CRIT "gettimeoffset(CPU %ld): missing %ld ticks!"
 218                         " cycles %lX prev/now/next %lX/%lX/%lX  clock %lX\n",
 219                         cpuid, elapsed_cycles / cpt,
 220                         elapsed_cycles, prev_tick, now, next_tick, cpt);
 221         }
 222
 223         /* FIXME: Can we improve the precision? Not with PAGE0. */
 224         usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec;
 225         return usec;
 226 #else
 227         return 0;
 228 #endif
 229 }
 230
 231 void
 232 do_gettimeofday (struct timeval *tv)
 233 {
 234         unsigned long flags, seq, usec, sec;
 235
 236         /* Hold xtime_lock and adjust timeval.  */
 237         do {
 238                 seq = read_seqbegin_irqsave(&xtime_lock, flags);
 239                 usec = gettimeoffset();
 240                 sec = xtime.tv_sec;
 241                 usec += (xtime.tv_nsec / 1000);
 242         } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
 243
 244         /* Move adjusted usec's into sec's.  */
 245         while (usec >= USEC_PER_SEC) {
 246                 usec -= USEC_PER_SEC;
 247                 ++sec;
 248         }
 249
 250         /* Return adjusted result.  */
 251         tv->tv_sec = sec;
 252         tv->tv_usec = usec;
 253 }
 254
 255 EXPORT_SYMBOL(do_gettimeofday);
 256
 257 int
 258 do_settimeofday (struct timespec *tv)
 259 {
 260         time_t wtm_sec, sec = tv->tv_sec;
 261         long wtm_nsec, nsec = tv->tv_nsec;
 262
 263         if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
 264                 return -EINVAL;
 265
 266         write_seqlock_irq(&xtime_lock);
 267         {
 268                 /*
 269                  * This is revolting. We need to set "xtime"
 270                  * correctly. However, the value in this location is
 271                  * the value at the most recent update of wall time.
 272                  * Discover what correction gettimeofday would have
 273                  * done, and then undo it!
 274                  */
 275                 nsec -= gettimeoffset() * 1000;
 276
 277                 wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
 278                 wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
 279
 280                 set_normalized_timespec(&xtime, sec, nsec);
 281                 set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
 282
 283                 ntp_clear();
 284         }
 285         write_sequnlock_irq(&xtime_lock);
 286         clock_was_set();
 287         return 0;
 288 }
 289 EXPORT_SYMBOL(do_settimeofday);
 290
 291 void __init start_cpu_itimer(void)
 292 {
 293         unsigned int cpu = smp_processor_id();
 294         unsigned long next_tick = mfctl(16) + clocktick;
 295
 296         mtctl(next_tick, 16);           /* kick off Interval Timer (CR16) */
 297
 298         cpu_data[cpu].it_value = next_tick;
 299 }
 300
 301 void __init time_init(void)
 302 {
 303         static struct pdc_tod tod_data;
 304
 305         clocktick = (100 * PAGE0->mem_10msec) / HZ;
 306
 307         start_cpu_itimer();     /* get CPU 0 started */
 308
 309         if (pdc_tod_read(&tod_data) == 0) {
 310                 unsigned long flags;
 311
 312                 write_seqlock_irqsave(&xtime_lock, flags);
 313                 xtime.tv_sec = tod_data.tod_sec;
 314                 xtime.tv_nsec = tod_data.tod_usec * 1000;
 315                 set_normalized_timespec(&wall_to_monotonic,
 316                                         -xtime.tv_sec, -xtime.tv_nsec);
 317                 write_sequnlock_irqrestore(&xtime_lock, flags);
 318         } else {
 319                 printk(KERN_ERR "Error reading tod clock\n");
 320                 xtime.tv_sec = 0;
 321                 xtime.tv_nsec = 0;
 322         }
 323 }
 324