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 #include <linux/clocksource.h>
  26
  27 #include <asm/uaccess.h>
  28 #include <asm/io.h>
  29 #include <asm/irq.h>
  30 #include <asm/param.h>
  31 #include <asm/pdc.h>
  32 #include <asm/led.h>
  33
  34 #include <linux/timex.h>
  35
  36 static unsigned long clocktick __read_mostly;   /* timer cycles per tick */
  37
  38 /*
  39  * We keep time on PA-RISC Linux by using the Interval Timer which is
  40  * a pair of registers; one is read-only and one is write-only; both
  41  * accessed through CR16.  The read-only register is 32 or 64 bits wide,
  42  * and increments by 1 every CPU clock tick.  The architecture only
  43  * guarantees us a rate between 0.5 and 2, but all implementations use a
  44  * rate of 1.  The write-only register is 32-bits wide.  When the lowest
  45  * 32 bits of the read-only register compare equal to the write-only
  46  * register, it raises a maskable external interrupt.  Each processor has
  47  * an Interval Timer of its own and they are not synchronised.
  48  *
  49  * We want to generate an interrupt every 1/HZ seconds.  So we program
  50  * CR16 to interrupt every @clocktick cycles.  The it_value in cpu_data
  51  * is programmed with the intended time of the next tick.  We can be
  52  * held off for an arbitrarily long period of time by interrupts being
  53  * disabled, so we may miss one or more ticks.
  54  */
  55 irqreturn_t timer_interrupt(int irq, void *dev_id)
  56 {
  57         unsigned long now;
  58         unsigned long next_tick;
  59         unsigned long cycles_elapsed, ticks_elapsed;
  60         unsigned long cycles_remainder;
  61         unsigned int cpu = smp_processor_id();
  62         struct cpuinfo_parisc *cpuinfo = &cpu_data[cpu];
  63
  64         /* gcc can optimize for "read-only" case with a local clocktick */
  65         unsigned long cpt = clocktick;
  66
  67         profile_tick(CPU_PROFILING);
  68
  69         /* Initialize next_tick to the expected tick time. */
  70         next_tick = cpuinfo->it_value;
  71
  72         /* Get current interval timer.
  73          * CR16 reads as 64 bits in CPU wide mode.
  74          * CR16 reads as 32 bits in CPU narrow mode.
  75          */
  76         now = mfctl(16);
  77
  78         cycles_elapsed = now - next_tick;
  79
  80         if ((cycles_elapsed >> 5) < cpt) {
  81                 /* use "cheap" math (add/subtract) instead
  82                  * of the more expensive div/mul method
  83                  */
  84                 cycles_remainder = cycles_elapsed;
  85                 ticks_elapsed = 1;
  86                 while (cycles_remainder > cpt) {
  87                         cycles_remainder -= cpt;
  88                         ticks_elapsed++;
  89                 }
  90         } else {
  91                 cycles_remainder = cycles_elapsed % cpt;
  92                 ticks_elapsed = 1 + cycles_elapsed / cpt;
  93         }
  94
  95         /* Can we differentiate between "early CR16" (aka Scenario 1) and
  96          * "long delay" (aka Scenario 3)? I don't think so.
  97          *
  98          * We expected timer_interrupt to be delivered at least a few hundred
  99          * cycles after the IT fires. But it's arbitrary how much time passes
 100          * before we call it "late". I've picked one second.
 101          */
 102         if (unlikely(ticks_elapsed > HZ)) {
 103                 /* Scenario 3: very long delay?  bad in any case */
 104                 printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
 105                         " cycles %lX rem %lX "
 106                         " next/now %lX/%lX\n",
 107                         cpu,
 108                         cycles_elapsed, cycles_remainder,
 109                         next_tick, now );
 110         }
 111
 112         /* convert from "division remainder" to "remainder of clock tick" */
 113         cycles_remainder = cpt - cycles_remainder;
 114
 115         /* Determine when (in CR16 cycles) next IT interrupt will fire.
 116          * We want IT to fire modulo clocktick even if we miss/skip some.
 117          * But those interrupts don't in fact get delivered that regularly.
 118          */
 119         next_tick = now + cycles_remainder;
 120
 121         cpuinfo->it_value = next_tick;
 122
 123         /* Skip one clocktick on purpose if we are likely to miss next_tick.
 124          * We want to avoid the new next_tick being less than CR16.
 125          * If that happened, itimer wouldn't fire until CR16 wrapped.
 126          * We'll catch the tick we missed on the tick after that.
 127          */
 128         if (!(cycles_remainder >> 13))
 129                 next_tick += cpt;
 130
 131         /* Program the IT when to deliver the next interrupt. */
 132         /* Only bottom 32-bits of next_tick are written to cr16.  */
 133         mtctl(next_tick, 16);
 134
 135
 136         /* Done mucking with unreliable delivery of interrupts.
 137          * Go do system house keeping.
 138          */
 139
 140         if (!--cpuinfo->prof_counter) {
 141                 cpuinfo->prof_counter = cpuinfo->prof_multiplier;
 142                 update_process_times(user_mode(get_irq_regs()));
 143         }
 144
 145         if (cpu == 0) {
 146                 write_seqlock(&xtime_lock);
 147                 do_timer(ticks_elapsed);
 148                 write_sequnlock(&xtime_lock);
 149         }
 150
 151         return IRQ_HANDLED;
 152 }
 153
 154
 155 unsigned long profile_pc(struct pt_regs *regs)
 156 {
 157         unsigned long pc = instruction_pointer(regs);
 158
 159         if (regs->gr[0] & PSW_N)
 160                 pc -= 4;
 161
 162 #ifdef CONFIG_SMP
 163         if (in_lock_functions(pc))
 164                 pc = regs->gr[2];
 165 #endif
 166
 167         return pc;
 168 }
 169 EXPORT_SYMBOL(profile_pc);
 170
 171
 172 /* clock source code */
 173
 174 static cycle_t read_cr16(void)
 175 {
 176         return get_cycles();
 177 }
 178
 179 static struct clocksource clocksource_cr16 = {
 180         .name                   = "cr16",
 181         .rating                 = 300,
 182         .read                   = read_cr16,
 183         .mask                   = CLOCKSOURCE_MASK(BITS_PER_LONG),
 184         .mult                   = 0, /* to be set */
 185         .shift                  = 22,
 186         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS,
 187 };
 188
 189 #ifdef CONFIG_SMP
 190 int update_cr16_clocksource(void)
 191 {
 192         /* since the cr16 cycle counters are not synchronized across CPUs,
 193            we'll check if we should switch to a safe clocksource: */
 194         if (clocksource_cr16.rating != 0 && num_online_cpus() > 1) {
 195                 clocksource_change_rating(&clocksource_cr16, 0);
 196                 return 1;
 197         }
 198
 199         return 0;
 200 }
 201 #else
 202 int update_cr16_clocksource(void)
 203 {
 204         return 0; /* no change */
 205 }
 206 #endif /*CONFIG_SMP*/
 207
 208 void __init start_cpu_itimer(void)
 209 {
 210         unsigned int cpu = smp_processor_id();
 211         unsigned long next_tick = mfctl(16) + clocktick;
 212
 213         mtctl(next_tick, 16);           /* kick off Interval Timer (CR16) */
 214
 215         cpu_data[cpu].it_value = next_tick;
 216 }
 217
 218 void __init time_init(void)
 219 {
 220         static struct pdc_tod tod_data;
 221         unsigned long current_cr16_khz;
 222
 223         clocktick = (100 * PAGE0->mem_10msec) / HZ;
 224
 225         start_cpu_itimer();     /* get CPU 0 started */
 226
 227         /* register at clocksource framework */
 228         current_cr16_khz = PAGE0->mem_10msec/10;  /* kHz */
 229         clocksource_cr16.mult = clocksource_khz2mult(current_cr16_khz,
 230                                                 clocksource_cr16.shift);
 231         clocksource_register(&clocksource_cr16);
 232
 233         if (pdc_tod_read(&tod_data) == 0) {
 234                 unsigned long flags;
 235
 236                 write_seqlock_irqsave(&xtime_lock, flags);
 237                 xtime.tv_sec = tod_data.tod_sec;
 238                 xtime.tv_nsec = tod_data.tod_usec * 1000;
 239                 set_normalized_timespec(&wall_to_monotonic,
 240                                         -xtime.tv_sec, -xtime.tv_nsec);
 241                 write_sequnlock_irqrestore(&xtime_lock, flags);
 242         } else {
 243                 printk(KERN_ERR "Error reading tod clock\n");
 244                 xtime.tv_sec = 0;
 245                 xtime.tv_nsec = 0;
 246         }
 247 }
 248