1 files changed, 139 insertions, 69 deletions

diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c
index ab641d67f551..b3496b592a2d 100644
--- a/arch/parisc/kernel/time.c
+++ b/arch/parisc/kernel/time.c
@@ -32,8 +32,7 @@
 
 #include <linux/timex.h>
 
-static long clocktick __read_mostly;    /* timer cycles per tick */
-static long halftick __read_mostly;
+static unsigned long clocktick __read_mostly;   /* timer cycles per tick */
 
 #ifdef CONFIG_SMP
 extern void smp_do_timer(struct pt_regs *regs);
@@ -41,46 +40,106 @@ extern void smp_do_timer(struct pt_regs *regs);
 
 irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 {
-        long now;
-        long next_tick;
-        int nticks;
-        int cpu = smp_processor_id();
+        unsigned long now;
+        unsigned long next_tick;
+        unsigned long cycles_elapsed;
+        unsigned long cycles_remainder;
+        unsigned int cpu = smp_processor_id();
+
+        /* gcc can optimize for "read-only" case with a local clocktick */
+        unsigned long cpt = clocktick;
 
         profile_tick(CPU_PROFILING, regs);
 
-        now = mfctl(16);
-        /* initialize next_tick to time at last clocktick */
+        /* Initialize next_tick to the expected tick time. */
         next_tick = cpu_data[cpu].it_value;
 
-        /* since time passes between the interrupt and the mfctl()
-         * above, it is never true that last_tick + clocktick == now.  If we
-         * never miss a clocktick, we could set next_tick = last_tick + clocktick
-         * but maybe we'll miss ticks, hence the loop.
-         *
-         * Variables are *signed*.
+        /* Get current interval timer.
+         * CR16 reads as 64 bits in CPU wide mode.
+         * CR16 reads as 32 bits in CPU narrow mode.
          */
+        now = mfctl(16);
+
+        cycles_elapsed = now - next_tick;
 
-        nticks = 0;
-        while((next_tick - now) < halftick) {
-                next_tick += clocktick;
-                nticks++;
+        if ((cycles_elapsed >> 5) < cpt) {
+                /* use "cheap" math (add/subtract) instead
+                 * of the more expensive div/mul method
+                 */
+                cycles_remainder = cycles_elapsed;
+                while (cycles_remainder > cpt) {
+                        cycles_remainder -= cpt;
+                }
+        } else {
+                cycles_remainder = cycles_elapsed % cpt;
         }
-        mtctl(next_tick, 16);
+
+        /* Can we differentiate between "early CR16" (aka Scenario 1) and
+         * "long delay" (aka Scenario 3)? I don't think so.
+         *
+         * We expected timer_interrupt to be delivered at least a few hundred
+         * cycles after the IT fires. But it's arbitrary how much time passes
+         * before we call it "late". I've picked one second.
+         */
+/* aproximate HZ with shifts. Intended math is "(elapsed/clocktick) > HZ" */
+#if HZ == 1000
+        if (cycles_elapsed > (cpt << 10) )
+#elif HZ == 250
+        if (cycles_elapsed > (cpt << 8) )
+#elif HZ == 100
+        if (cycles_elapsed > (cpt << 7) )
+#else
+#warn WTF is HZ set to anyway?
+        if (cycles_elapsed > (HZ * cpt) )
+#endif
+        {
+                /* Scenario 3: very long delay?  bad in any case */
+                printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
+                        " cycles %lX rem %lX "
+                        " next/now %lX/%lX\n",
+                        cpu,
+                        cycles_elapsed, cycles_remainder,
+                        next_tick, now );
+        }
+
+        /* convert from "division remainder" to "remainder of clock tick" */
+        cycles_remainder = cpt - cycles_remainder;
+
+        /* Determine when (in CR16 cycles) next IT interrupt will fire.
+         * We want IT to fire modulo clocktick even if we miss/skip some.
+         * But those interrupts don't in fact get delivered that regularly.
+         */
+        next_tick = now + cycles_remainder;
+
         cpu_data[cpu].it_value = next_tick;
 
-        while (nticks--) {
+        /* Skip one clocktick on purpose if we are likely to miss next_tick.
+         * We want to avoid the new next_tick being less than CR16.
+         * If that happened, itimer wouldn't fire until CR16 wrapped.
+         * We'll catch the tick we missed on the tick after that.
+         */
+        if (!(cycles_remainder >> 13))
+                next_tick += cpt;
+
+        /* Program the IT when to deliver the next interrupt. */
+        /* Only bottom 32-bits of next_tick are written to cr16.  */
+        mtctl(next_tick, 16);
+
+
+        /* Done mucking with unreliable delivery of interrupts.
+         * Go do system house keeping.
+         */
 #ifdef CONFIG_SMP
-                smp_do_timer(regs);
+        smp_do_timer(regs);
 #else
-                update_process_times(user_mode(regs));
+        update_process_times(user_mode(regs));
 #endif
-                if (cpu == 0) {
-                        write_seqlock(&xtime_lock);
-                        do_timer(1);
-                        write_sequnlock(&xtime_lock);
-                }
+        if (cpu == 0) {
+                write_seqlock(&xtime_lock);
+                do_timer(regs);
+                write_sequnlock(&xtime_lock);
         }
-    
+
         /* check soft power switch status */
         if (cpu == 0 && !atomic_read(&power_tasklet.count))
                 tasklet_schedule(&power_tasklet);
@@ -106,14 +165,12 @@ unsigned long profile_pc(struct pt_regs *regs)
 EXPORT_SYMBOL(profile_pc);
 
 
-/*** converted from ia64 ***/
 /*
  * Return the number of micro-seconds that elapsed since the last
  * update to wall time (aka xtime).  The xtime_lock
  * must be at least read-locked when calling this routine.
  */
-static inline unsigned long
-gettimeoffset (void)
+static inline unsigned long gettimeoffset (void)
 {
 #ifndef CONFIG_SMP
         /*
@@ -121,21 +178,44 @@ gettimeoffset (void)
          *    Once parisc-linux learns the cr16 difference between processors,
          *    this could be made to work.
          */
-        long last_tick;
-        long elapsed_cycles;
-
-        /* it_value is the intended time of the next tick */
-        last_tick = cpu_data[smp_processor_id()].it_value;
-
-        /* Subtract one tick and account for possible difference between
-         * when we expected the tick and when it actually arrived.
-         * (aka wall vs real)
-         */
-        last_tick -= clocktick * (jiffies - wall_jiffies + 1);
-        elapsed_cycles = mfctl(16) - last_tick;
+        unsigned long now;
+        unsigned long prev_tick;
+        unsigned long next_tick;
+        unsigned long elapsed_cycles;
+        unsigned long usec;
+        unsigned long cpuid = smp_processor_id();
+        unsigned long cpt = clocktick;
+
+        next_tick = cpu_data[cpuid].it_value;
+        now = mfctl(16);        /* Read the hardware interval timer.  */
+
+        prev_tick = next_tick - cpt;
+
+        /* Assume Scenario 1: "now" is later than prev_tick.  */
+        elapsed_cycles = now - prev_tick;
+
+/* aproximate HZ with shifts. Intended math is "(elapsed/clocktick) > HZ" */
+#if HZ == 1000
+        if (elapsed_cycles > (cpt << 10) )
+#elif HZ == 250
+        if (elapsed_cycles > (cpt << 8) )
+#elif HZ == 100
+        if (elapsed_cycles > (cpt << 7) )
+#else
+#warn WTF is HZ set to anyway?
+        if (elapsed_cycles > (HZ * cpt) )
+#endif
+        {
+                /* Scenario 3: clock ticks are missing. */
+                printk (KERN_CRIT "gettimeoffset(CPU %ld): missing %ld ticks!"
+                        " cycles %lX prev/now/next %lX/%lX/%lX  clock %lX\n",
+                        cpuid, elapsed_cycles / cpt,
+                        elapsed_cycles, prev_tick, now, next_tick, cpt);
+        }
 
-        /* the precision of this math could be improved */
-        return elapsed_cycles / (PAGE0->mem_10msec / 10000);
+        /* FIXME: Can we improve the precision? Not with PAGE0. */
+        usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec;
+        return usec;
 #else
         return 0;
 #endif
@@ -146,6 +226,7 @@ do_gettimeofday (struct timeval *tv)
 {
         unsigned long flags, seq, usec, sec;
 
+        /* Hold xtime_lock and adjust timeval.  */
         do {
                 seq = read_seqbegin_irqsave(&xtime_lock, flags);
                 usec = gettimeoffset();
@@ -153,25 +234,13 @@ do_gettimeofday (struct timeval *tv)
                 usec += (xtime.tv_nsec / 1000);
         } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
 
-        if (unlikely(usec > LONG_MAX)) {
-                /* This can happen if the gettimeoffset adjustment is
-                 * negative and xtime.tv_nsec is smaller than the
-                 * adjustment */
-                printk(KERN_ERR "do_gettimeofday() spurious xtime.tv_nsec of %ld\n", usec);
-                usec += USEC_PER_SEC;
-                --sec;
-                /* This should never happen, it means the negative
-                 * time adjustment was more than a second, so there's
-                 * something seriously wrong */
-                BUG_ON(usec > LONG_MAX);
-        }
-
-
+        /* Move adjusted usec's into sec's.  */
         while (usec >= USEC_PER_SEC) {
                 usec -= USEC_PER_SEC;
                 ++sec;
         }
 
+        /* Return adjusted result.  */
         tv->tv_sec = sec;
         tv->tv_usec = usec;
 }
@@ -223,22 +292,23 @@ unsigned long long sched_clock(void)
 }
 
 
+void __init start_cpu_itimer(void)
+{
+        unsigned int cpu = smp_processor_id();
+        unsigned long next_tick = mfctl(16) + clocktick;
+
+        mtctl(next_tick, 16);           /* kick off Interval Timer (CR16) */
+
+        cpu_data[cpu].it_value = next_tick;
+}
+
 void __init time_init(void)
 {
-        unsigned long next_tick;
         static struct pdc_tod tod_data;
 
         clocktick = (100 * PAGE0->mem_10msec) / HZ;
-        halftick = clocktick / 2;
 
-        /* Setup clock interrupt timing */
-
-        next_tick = mfctl(16);
-        next_tick += clocktick;
-        cpu_data[smp_processor_id()].it_value = next_tick;
-
-        /* kick off Itimer (CR16) */
-        mtctl(next_tick, 16);
+        start_cpu_itimer();     /* get CPU 0 started */
 
         if(pdc_tod_read(&tod_data) == 0) {
                 write_seqlock_irq(&xtime_lock);