1/*
  2 * Delay loops based on the OpenRISC implementation.
  3 *
  4 * Copyright (C) 2012 ARM Limited
  5 *
  6 * This program is free software; you can redistribute it and/or modify
  7 * it under the terms of the GNU General Public License version 2 as
  8 * published by the Free Software Foundation.
  9 *
 10 * This program is distributed in the hope that it will be useful,
 11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 13 * GNU General Public License for more details.
 14 *
 15 * You should have received a copy of the GNU General Public License
 16 * along with this program; if not, write to the Free Software
 17 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 18 *
 19 * Author: Will Deacon <will.deacon@arm.com>
 20 */
 21
 22#include <linux/clocksource.h>
 23#include <linux/delay.h>
 24#include <linux/init.h>
 25#include <linux/kernel.h>
 26#include <linux/module.h>
 27#include <linux/timex.h>
 28
 29/*
 30 * Default to the loop-based delay implementation.
 31 */
 32struct arm_delay_ops arm_delay_ops = {
 33	.delay		= __loop_delay,
 34	.const_udelay	= __loop_const_udelay,
 35	.udelay		= __loop_udelay,
 36};
 37
 38static const struct delay_timer *delay_timer;
 39static bool delay_calibrated;
 40static u64 delay_res;
 41
 42int read_current_timer(unsigned long *timer_val)
 43{
 44	if (!delay_timer)
 45		return -ENXIO;
 46
 47	*timer_val = delay_timer->read_current_timer();
 48	return 0;
 49}
 50EXPORT_SYMBOL_GPL(read_current_timer);
 51
 52static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
 53{
 54	return (cyc * mult) >> shift;
 55}
 56
 57static void __timer_delay(unsigned long cycles)
 58{
 59	cycles_t start = get_cycles();
 60
 61	while ((get_cycles() - start) < cycles)
 62		cpu_relax();
 63}
 64
 65static void __timer_const_udelay(unsigned long xloops)
 66{
 67	unsigned long long loops = xloops;
 68	loops *= arm_delay_ops.ticks_per_jiffy;
 69	__timer_delay(loops >> UDELAY_SHIFT);
 70}
 71
 72static void __timer_udelay(unsigned long usecs)
 73{
 74	__timer_const_udelay(usecs * UDELAY_MULT);
 75}
 76
 77void __init register_current_timer_delay(const struct delay_timer *timer)
 78{
 79	u32 new_mult, new_shift;
 80	u64 res;
 81
 82	clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
 83			       NSEC_PER_SEC, 3600);
 84	res = cyc_to_ns(1ULL, new_mult, new_shift);
 85
 86	if (res > 1000) {
 87		pr_err("Ignoring delay timer %ps, which has insufficient resolution of %lluns\n",
 88			timer, res);
 89		return;
 90	}
 91
 92	if (!delay_calibrated && (!delay_res || (res < delay_res))) {
 93		pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
 94		delay_timer			= timer;
 95		lpj_fine			= timer->freq / HZ;
 96		delay_res			= res;
 97
 98		/* cpufreq may scale loops_per_jiffy, so keep a private copy */
 99		arm_delay_ops.ticks_per_jiffy	= lpj_fine;
100		arm_delay_ops.delay		= __timer_delay;
101		arm_delay_ops.const_udelay	= __timer_const_udelay;
102		arm_delay_ops.udelay		= __timer_udelay;
103	} else {
104		pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
105	}
106}
107
108unsigned long calibrate_delay_is_known(void)
109{
110	delay_calibrated = true;
111	return lpj_fine;
112}
113
114void calibration_delay_done(void)
115{
116	delay_calibrated = true;
117}