[PARISC] Rewrite timer_interrupt() and gettimeoffset() using "unsigned" math.

#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 */

static unsigned long halftick __read_mostly;

#ifdef CONFIG_SMP

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;

	unsigned long now;

	unsigned long next_tick;

	unsigned long cycles_elapsed;

        unsigned long cycles_remainder;

	unsigned long ticks_elapsed = 1;	/* at least one elapsed */

	int cpu = smp_processor_id();

	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.

	/* 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;

	/* Determine how much time elapsed.  */

	if (now < next_tick) {

		/* Scenario 2: CR16 wrapped after clock tick.

		 * 1's complement will give us the "elapse cycles".

		 *

	 * Variables are *signed*.

		 * This "cr16 wrapped" cruft is primarily for 32-bit kernels.

		 * So think "unsigned long is u32" when reading the code.

		 * And yes, of course 64-bit will someday wrap, but only

	  	 * every 198841 days on a 1GHz machine.

		 */

		cycles_elapsed = ~cycles_elapsed;   /* off by one cycle - don't care */

	}

	nticks = 0;

	while((next_tick - now) < halftick) {

		next_tick += clocktick;

		nticks++;

	ticks_elapsed += cycles_elapsed / clocktick;

	cycles_remainder = cycles_elapsed % clocktick;

	/* 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.

	 */

	if (ticks_elapsed > HZ) {

		/* Scenario 3: very long delay?  bad in any case */

		printk (KERN_CRIT "timer_interrupt(CPU %d): delayed! run ntpdate"

			" ticks %ld cycles %lX rem %lX"

			" next/now %lX/%lX\n",

			cpu,

			ticks_elapsed, cycles_elapsed, cycles_remainder,

			next_tick, now );

		ticks_elapsed = 1;	/* hack to limit damage in loop below */

	}

	/* 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 + (clocktick - cycles_remainder);

	/* Program the IT when to deliver the next interrupt. */

        /* Only bottom 32-bits of next_tick are written to cr16.  */

	mtctl(next_tick, 16);

	cpu_data[cpu].it_value = next_tick;

	while (nticks--) {

	/* Now that we are done mucking with unreliable delivery of interrupts,

	 * go do system house keeping.

	 */

	while (ticks_elapsed--) {

#ifdef CONFIG_SMP

		smp_do_timer(regs);

#else

	 *    Once parisc-linux learns the cr16 difference between processors,

	 *    this could be made to work.

	 */

	long last_tick;

	long elapsed_cycles;

	unsigned long now;

	unsigned long prev_tick;

	unsigned long next_tick;

	unsigned long elapsed_cycles;

	unsigned long usec;

	next_tick = cpu_data[smp_processor_id()].it_value;

	now = mfctl(16);	/* Read the hardware interval timer.  */

	/* it_value is the intended time of the next tick */

	last_tick = cpu_data[smp_processor_id()].it_value;

	prev_tick = next_tick - clocktick;

	/* Subtract one tick and account for possible difference between

	 * when we expected the tick and when it actually arrived.

	 * (aka wall vs real)

	/* Assume Scenario 1: "now" is later than prev_tick.  */

	elapsed_cycles = now - prev_tick;

	if (now < prev_tick) {

		/* Scenario 2: CR16 wrapped!

		 * 1's complement is close enough.

		 */

	last_tick -= clocktick * (jiffies - wall_jiffies + 1);

	elapsed_cycles = mfctl(16) - last_tick;

		elapsed_cycles = ~elapsed_cycles;

	}

	/* the precision of this math could be improved */

	return elapsed_cycles / (PAGE0->mem_10msec / 10000);

	if (elapsed_cycles > (HZ * clocktick)) {

		/* Scenario 3: clock ticks are missing. */

		printk (KERN_CRIT "gettimeoffset(CPU %d): missing ticks!"

			"cycles %lX prev/now/next %lX/%lX/%lX  clock %lX\n",

			cpuid,

			elapsed_cycles, prev_tick, now, next_tick, clocktick);

	}

	/* FIXME: Can we improve the precision? Not with PAGE0. */

	usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec;

	/* add in "lost" jiffies */

	usec += clocktick * (jiffies - wall_jiffies);

	return usec;

#else

	return 0;

#endif

{

	unsigned long flags, seq, usec, sec;

	/* Hold xtime_lock and adjust timeval.  */

	do {

		seq = read_seqbegin_irqsave(&xtime_lock, flags);

		usec = gettimeoffset();

		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;

}