/*
* linux/arch/parisc/kernel/time.c
*
* Copyright (C) 1991, 1992, 1995 Linus Torvalds
* Modifications for ARM (C) 1994, 1995, 1996,1997 Russell King
* Copyright (C) 1999 SuSE GmbH, (Philipp Rumpf, prumpf@tux.org)
*
* 1994-07-02 Alan Modra
* fixed set_rtc_mmss, fixed time.year for >= 2000, new mktime
* 1998-12-20 Updated NTP code according to technical memorandum Jan '96
* "A Kernel Model for Precision Timekeeping" by Dave Mills
*/
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/param.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/profile.h>
#include <linux/clocksource.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/param.h>
#include <asm/pdc.h>
#include <asm/led.h>
#include <linux/timex.h>
static unsigned long clocktick __read_mostly; /* timer cycles per tick */
/*
* We keep time on PA-RISC Linux by using the Interval Timer which is
* a pair of registers; one is read-only and one is write-only; both
* accessed through CR16. The read-only register is 32 or 64 bits wide,
* and increments by 1 every CPU clock tick. The architecture only
* guarantees us a rate between 0.5 and 2, but all implementations use a
* rate of 1. The write-only register is 32-bits wide. When the lowest
* 32 bits of the read-only register compare equal to the write-only
* register, it raises a maskable external interrupt. Each processor has
* an Interval Timer of its own and they are not synchronised.
*
* We want to generate an interrupt every 1/HZ seconds. So we program
* CR16 to interrupt every @clocktick cycles. The it_value in cpu_data
* is programmed with the intended time of the next tick. We can be
* held off for an arbitrarily long period of time by interrupts being
* disabled, so we may miss one or more ticks.
*/
irqreturn_t timer_interrupt(int irq, void *dev_id)
{
unsigned long now;
unsigned long next_tick;
unsigned long cycles_elapsed, ticks_elapsed;
unsigned long cycles_remainder;
unsigned int cpu = smp_processor_id();
struct cpuinfo_parisc *cpuinfo = &cpu_data[cpu];
/* gcc can optimize for "read-only" case with a local clocktick */
unsigned long cpt = clocktick;
profile_tick(CPU_PROFILING);
/* Initialize next_tick to the expected tick time. */
next_tick = cpuinfo->it_value;
/* 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;
if ((cycles_elapsed >> 5) < cpt) {
/* use "cheap" math (add/subtract) instead
* of the more expensive div/mul method
*/
cycles_remainder = cycles_elapsed;
ticks_elapsed = 1;
while (cycles_remainder > cpt) {
cycles_remainder -= cpt;
ticks_elapsed++;
}
} else {
cycles_remainder = cycles_elapsed % cpt;
ticks_elapsed = 1 + cycles_elapsed / cpt;
}
/* 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 (unlikely(ticks_elapsed > HZ)) {
/* 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;
cpuinfo->it_value = next_tick;
/* 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.
*/
if (!--cpuinfo->prof_counter) {
cpuinfo->prof_counter = cpuinfo->prof_multiplier;
update_process_times(user_mode(get_irq_regs()));
}
if (cpu == 0) {
write_seqlock(&xtime_lock);
do_timer(ticks_elapsed);
write_sequnlock(&xtime_lock);
}
return IRQ_HANDLED;
}
unsigned long profile_pc(struct pt_regs *regs)
{
unsigned long pc = instruction_pointer(regs);
if (regs->gr[0] & PSW_N)
pc -= 4;
#ifdef CONFIG_SMP
if (in_lock_functions(pc))
pc = regs->gr[2];
#endif
return pc;
}
EXPORT_SYMBOL(profile_pc);
/* clock source code */
static cycle_t read_cr16(void)
{
return get_cycles();
}
static int cr16_update_callback(void);
static struct clocksource clocksource_cr16 = {
.name = "cr16",
.rating = 300,
.read = read_cr16,
.mask = CLOCKSOURCE_MASK(BITS_PER_LONG),
.mult = 0, /* to be set */
.shift = 22,
.update_callback = cr16_update_callback,
.is_continuous = 1,
};
static int cr16_update_callback(void)
{
int change = 0;
/* since the cr16 cycle counters are not syncronized across CPUs,
we'll check if we should switch to a safe clocksource: */
if (clocksource_cr16.rating != 0 && num_online_cpus() > 1) {
clocksource_cr16.rating = 0;
clocksource_reselect();
change = 1;
}
return change;
}
/*
* XXX: We can do better than this.
* Returns nanoseconds
*/
unsigned long long sched_clock(void)
{
return (unsigned long long)jiffies * (1000000000 / HZ);
}
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)
{
static struct pdc_tod tod_data;
unsigned long current_cr16_khz;
clocktick = (100 * PAGE0->mem_10msec) / HZ;
start_cpu_itimer(); /* get CPU 0 started */
/* register at clocksource framework */
current_cr16_khz = PAGE0->mem_10msec/10; /* kHz */
clocksource_cr16.mult = clocksource_khz2mult(current_cr16_khz,
clocksource_cr16.shift);
clocksource_register(&clocksource_cr16);
if (pdc_tod_read(&tod_data) == 0) {
unsigned long flags;
write_seqlock_irqsave(&xtime_lock, flags);
xtime.tv_sec = tod_data.tod_sec;
xtime.tv_nsec = tod_data.tod_usec * 1000;
set_normalized_timespec(&wall_to_monotonic,
-xtime.tv_sec, -xtime.tv_nsec);
write_sequnlock_irqrestore(&xtime_lock, flags);
} else {
printk(KERN_ERR "Error reading tod clock\n");
xtime.tv_sec = 0;
xtime.tv_nsec = 0;
}
}
