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/*
* sched_clock.c: support for extending counters to full 64-bit ns counter
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <asm/sched_clock.h>
static void sched_clock_poll(unsigned long wrap_ticks);
static DEFINE_TIMER(sched_clock_timer, sched_clock_poll, 0, 0);
static void (*sched_clock_update_fn)(void);
static void sched_clock_poll(unsigned long wrap_ticks)
{
mod_timer(&sched_clock_timer, round_jiffies(jiffies + wrap_ticks));
sched_clock_update_fn();
}
void __init init_sched_clock(struct clock_data *cd, void (*update)(void),
unsigned int clock_bits, unsigned long rate)
{
unsigned long r, w;
u64 res, wrap;
char r_unit;
sched_clock_update_fn = update;
/* calculate the mult/shift to convert counter ticks to ns. */
clocks_calc_mult_shift(&cd->mult, &cd->shift, rate, NSEC_PER_SEC, 60);
r = rate;
if (r >= 4000000) {
r /= 1000000;
r_unit = 'M';
} else {
r /= 1000;
r_unit = 'k';
}
/* calculate how many ns until we wrap */
wrap = cyc_to_ns((1ULL << clock_bits) - 1, cd->mult, cd->shift);
do_div(wrap, NSEC_PER_MSEC);
w = wrap;
/* calculate the ns resolution of this counter */
res = cyc_to_ns(1ULL, cd->mult, cd->shift);
pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n",
clock_bits, r, r_unit, res, w);
/*
* Start the timer to keep sched_clock() properly updated and
* sets the initial epoch.
*/
sched_clock_timer.data = msecs_to_jiffies(w - (w / 10));
sched_clock_poll(sched_clock_timer.data);
/*
* Ensure that sched_clock() starts off at 0ns
*/
cd->epoch_ns = 0;
}
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