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 #include <linux/platform_device.h>
  27 #include <linux/ftrace.h>
  28
  29 #include <asm/uaccess.h>
  30 #include <asm/io.h>
  31 #include <asm/irq.h>
  32 #include <asm/param.h>
  33 #include <asm/pdc.h>
  34 #include <asm/led.h>
  35
  36 #include <linux/timex.h>
  37
  38 static unsigned long clocktick __read_mostly;   /* timer cycles per tick */
  39
  40 /*
  41  * We keep time on PA-RISC Linux by using the Interval Timer which is
  42  * a pair of registers; one is read-only and one is write-only; both
  43  * accessed through CR16.  The read-only register is 32 or 64 bits wide,
  44  * and increments by 1 every CPU clock tick.  The architecture only
  45  * guarantees us a rate between 0.5 and 2, but all implementations use a
  46  * rate of 1.  The write-only register is 32-bits wide.  When the lowest
  47  * 32 bits of the read-only register compare equal to the write-only
  48  * register, it raises a maskable external interrupt.  Each processor has
  49  * an Interval Timer of its own and they are not synchronised.
  50  *
  51  * We want to generate an interrupt every 1/HZ seconds.  So we program
  52  * CR16 to interrupt every @clocktick cycles.  The it_value in cpu_data
  53  * is programmed with the intended time of the next tick.  We can be
  54  * held off for an arbitrarily long period of time by interrupts being
  55  * disabled, so we may miss one or more ticks.
  56  */
  57 irqreturn_t __irq_entry timer_interrupt(int irq, void *dev_id)
  58 {
  59         unsigned long now, now2;
  60         unsigned long next_tick;
  61         unsigned long cycles_elapsed, ticks_elapsed = 1;
  62         unsigned long cycles_remainder;
  63         unsigned int cpu = smp_processor_id();
  64         struct cpuinfo_parisc *cpuinfo = &per_cpu(cpu_data, cpu);
  65
  66         /* gcc can optimize for "read-only" case with a local clocktick */
  67         unsigned long cpt = clocktick;
  68
  69         profile_tick(CPU_PROFILING);
  70
  71         /* Initialize next_tick to the expected tick time. */
  72         next_tick = cpuinfo->it_value;
  73
  74         /* Get current cycle counter (Control Register 16). */
  75         now = mfctl(16);
  76
  77         cycles_elapsed = now - next_tick;
  78
  79         if ((cycles_elapsed >> 6) < cpt) {
  80                 /* use "cheap" math (add/subtract) instead
  81                  * of the more expensive div/mul method
  82                  */
  83                 cycles_remainder = cycles_elapsed;
  84                 while (cycles_remainder > cpt) {
  85                         cycles_remainder -= cpt;
  86                         ticks_elapsed++;
  87                 }
  88         } else {
  89                 /* TODO: Reduce this to one fdiv op */
  90                 cycles_remainder = cycles_elapsed % cpt;
  91                 ticks_elapsed += cycles_elapsed / cpt;
  92         }
  93
  94         /* convert from "division remainder" to "remainder of clock tick" */
  95         cycles_remainder = cpt - cycles_remainder;
  96
  97         /* Determine when (in CR16 cycles) next IT interrupt will fire.
  98          * We want IT to fire modulo clocktick even if we miss/skip some.
  99          * But those interrupts don't in fact get delivered that regularly.
 100          */
 101         next_tick = now + cycles_remainder;
 102
 103         cpuinfo->it_value = next_tick;
 104
 105         /* Program the IT when to deliver the next interrupt.
 106          * Only bottom 32-bits of next_tick are writable in CR16!
 107          */
 108         mtctl(next_tick, 16);
 109
 110         /* Skip one clocktick on purpose if we missed next_tick.
 111          * The new CR16 must be "later" than current CR16 otherwise
 112          * itimer would not fire until CR16 wrapped - e.g 4 seconds
 113          * later on a 1Ghz processor. We'll account for the missed
 114          * tick on the next timer interrupt.
 115          *
 116          * "next_tick - now" will always give the difference regardless
 117          * if one or the other wrapped. If "now" is "bigger" we'll end up
 118          * with a very large unsigned number.
 119          */
 120         now2 = mfctl(16);
 121         if (next_tick - now2 > cpt)
 122                 mtctl(next_tick+cpt, 16);
 123
 124 #if 1
 125 /*
 126  * GGG: DEBUG code for how many cycles programming CR16 used.
 127  */
 128         if (unlikely(now2 - now > 0x3000))      /* 12K cycles */
 129                 printk (KERN_CRIT "timer_interrupt(CPU %d): SLOW! 0x%lx cycles!"
 130                         " cyc %lX rem %lX "
 131                         " next/now %lX/%lX\n",
 132                         cpu, now2 - now, cycles_elapsed, cycles_remainder,
 133                         next_tick, now );
 134 #endif
 135
 136         /* Can we differentiate between "early CR16" (aka Scenario 1) and
 137          * "long delay" (aka Scenario 3)? I don't think so.
 138          *
 139          * Timer_interrupt will be delivered at least a few hundred cycles
 140          * after the IT fires. But it's arbitrary how much time passes
 141          * before we call it "late". I've picked one second.
 142          *
 143          * It's important NO printk's are between reading CR16 and
 144          * setting up the next value. May introduce huge variance.
 145          */
 146         if (unlikely(ticks_elapsed > HZ)) {
 147                 /* Scenario 3: very long delay?  bad in any case */
 148                 printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
 149                         " cycles %lX rem %lX "
 150                         " next/now %lX/%lX\n",
 151                         cpu,
 152                         cycles_elapsed, cycles_remainder,
 153                         next_tick, now );
 154         }
 155
 156         /* Done mucking with unreliable delivery of interrupts.
 157          * Go do system house keeping.
 158          */
 159
 160         if (!--cpuinfo->prof_counter) {
 161                 cpuinfo->prof_counter = cpuinfo->prof_multiplier;
 162                 update_process_times(user_mode(get_irq_regs()));
 163         }
 164
 165         if (cpu == 0) {
 166                 write_seqlock(&xtime_lock);
 167                 do_timer(ticks_elapsed);
 168                 write_sequnlock(&xtime_lock);
 169         }
 170
 171         return IRQ_HANDLED;
 172 }
 173
 174
 175 unsigned long profile_pc(struct pt_regs *regs)
 176 {
 177         unsigned long pc = instruction_pointer(regs);
 178
 179         if (regs->gr[0] & PSW_N)
 180                 pc -= 4;
 181
 182 #ifdef CONFIG_SMP
 183         if (in_lock_functions(pc))
 184                 pc = regs->gr[2];
 185 #endif
 186
 187         return pc;
 188 }
 189 EXPORT_SYMBOL(profile_pc);
 190
 191
 192 /* clock source code */
 193
 194 static cycle_t read_cr16(struct clocksource *cs)
 195 {
 196         return get_cycles();
 197 }
 198
 199 static struct clocksource clocksource_cr16 = {
 200         .name                   = "cr16",
 201         .rating                 = 300,
 202         .read                   = read_cr16,
 203         .mask                   = CLOCKSOURCE_MASK(BITS_PER_LONG),
 204         .mult                   = 0, /* to be set */
 205         .shift                  = 22,
 206         .flags                  = CLOCK_SOURCE_IS_CONTINUOUS,
 207 };
 208
 209 #ifdef CONFIG_SMP
 210 int update_cr16_clocksource(void)
 211 {
 212         /* since the cr16 cycle counters are not synchronized across CPUs,
 213            we'll check if we should switch to a safe clocksource: */
 214         if (clocksource_cr16.rating != 0 && num_online_cpus() > 1) {
 215                 clocksource_change_rating(&clocksource_cr16, 0);
 216                 return 1;
 217         }
 218
 219         return 0;
 220 }
 221 #else
 222 int update_cr16_clocksource(void)
 223 {
 224         return 0; /* no change */
 225 }
 226 #endif /*CONFIG_SMP*/
 227
 228 void __init start_cpu_itimer(void)
 229 {
 230         unsigned int cpu = smp_processor_id();
 231         unsigned long next_tick = mfctl(16) + clocktick;
 232
 233         mtctl(next_tick, 16);           /* kick off Interval Timer (CR16) */
 234
 235         per_cpu(cpu_data, cpu).it_value = next_tick;
 236 }
 237
 238 static struct platform_device rtc_generic_dev = {
 239         .name = "rtc-generic",
 240         .id = -1,
 241 };
 242
 243 static int __init rtc_init(void)
 244 {
 245         if (platform_device_register(&rtc_generic_dev) < 0)
 246                 printk(KERN_ERR "unable to register rtc device...\n");
 247
 248         /* not necessarily an error */
 249         return 0;
 250 }
 251 module_init(rtc_init);
 252
 253 void read_persistent_clock(struct timespec *ts)
 254 {
 255         static struct pdc_tod tod_data;
 256         if (pdc_tod_read(&tod_data) == 0) {
 257                 ts->tv_sec = tod_data.tod_sec;
 258                 ts->tv_nsec = tod_data.tod_usec * 1000;
 259         } else {
 260                 printk(KERN_ERR "Error reading tod clock\n");
 261                 ts->tv_sec = 0;
 262                 ts->tv_nsec = 0;
 263         }
 264 }
 265
 266 void __init time_init(void)
 267 {
 268         unsigned long current_cr16_khz;
 269
 270         clocktick = (100 * PAGE0->mem_10msec) / HZ;
 271
 272         start_cpu_itimer();     /* get CPU 0 started */
 273
 274         /* register at clocksource framework */
 275         current_cr16_khz = PAGE0->mem_10msec/10;  /* kHz */
 276         clocksource_cr16.mult = clocksource_khz2mult(current_cr16_khz,
 277                                                 clocksource_cr16.shift);
 278         clocksource_register(&clocksource_cr16);
 279 }