1/*
 2 * sched_clock.c: support for extending counters to full 64-bit ns counter
 3 *
 4 * This program is free software; you can redistribute it and/or modify
 5 * it under the terms of the GNU General Public License version 2 as
 6 * published by the Free Software Foundation.
 7 */
 8#include <linux/clocksource.h>
 9#include <linux/init.h>
10#include <linux/jiffies.h>
11#include <linux/kernel.h>
12#include <linux/sched.h>
13#include <linux/timer.h>
14
15#include <asm/sched_clock.h>
16
17static void sched_clock_poll(unsigned long wrap_ticks);
18static DEFINE_TIMER(sched_clock_timer, sched_clock_poll, 0, 0);
19static void (*sched_clock_update_fn)(void);
20
21static void sched_clock_poll(unsigned long wrap_ticks)
22{
23	mod_timer(&sched_clock_timer, round_jiffies(jiffies + wrap_ticks));
24	sched_clock_update_fn();
25}
26
27void __init init_sched_clock(struct clock_data *cd, void (*update)(void),
28	unsigned int clock_bits, unsigned long rate)
29{
30	unsigned long r, w;
31	u64 res, wrap;
32	char r_unit;
33
34	sched_clock_update_fn = update;
35
36	/* calculate the mult/shift to convert counter ticks to ns. */
37	clocks_calc_mult_shift(&cd->mult, &cd->shift, rate, NSEC_PER_SEC, 0);
38
39	r = rate;
40	if (r >= 4000000) {
41		r /= 1000000;
42		r_unit = 'M';
43	} else {
44		r /= 1000;
45		r_unit = 'k';
46	}
47
48	/* calculate how many ns until we wrap */
49	wrap = cyc_to_ns((1ULL << clock_bits) - 1, cd->mult, cd->shift);
50	do_div(wrap, NSEC_PER_MSEC);
51	w = wrap;
52
53	/* calculate the ns resolution of this counter */
54	res = cyc_to_ns(1ULL, cd->mult, cd->shift);
55	pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n",
56		clock_bits, r, r_unit, res, w);
57
58	/*
59	 * Start the timer to keep sched_clock() properly updated and
60	 * sets the initial epoch.
61	 */
62	sched_clock_timer.data = msecs_to_jiffies(w - (w / 10));
63	update();
64
65	/*
66	 * Ensure that sched_clock() starts off at 0ns
67	 */
68	cd->epoch_ns = 0;
69}
70
71void __init sched_clock_postinit(void)
72{
73	sched_clock_poll(sched_clock_timer.data);
74}