delay.c

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/*
 * Delay loops based on the OpenRISC implementation.
 *
 * Copyright (C) 2012 ARM Limited
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * Author: Will Deacon <[email protected]>
 */

#include <linux/delay.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/timex.h>

/*
 * Default to the loop-based delay implementation.
 */
struct arm_delay_ops arm_delay_ops = {
    .delay      = __loop_delay,
    .const_udelay   = __loop_const_udelay,
    .udelay     = __loop_udelay,
};

static const struct delay_timer *delay_timer;
static bool delay_calibrated;

int read_current_timer(unsigned long *timer_val)
{
    if (!delay_timer)
        return -ENXIO;

    *timer_val = delay_timer->read_current_timer();
    return 0;
}
EXPORT_SYMBOL_GPL(read_current_timer);

static void __timer_delay(unsigned long cycles)
{
    cycles_t start = get_cycles();

    while ((get_cycles() - start) < cycles)
        cpu_relax();
}

static void __timer_const_udelay(unsigned long xloops)
{
    unsigned long long loops = xloops;
    loops *= loops_per_jiffy;
    __timer_delay(loops >> UDELAY_SHIFT);
}

static void __timer_udelay(unsigned long usecs)
{
    __timer_const_udelay(usecs * UDELAY_MULT);
}

void __init register_current_timer_delay(const struct delay_timer *timer)
{
    if (!delay_calibrated) {
        pr_info("Switching to timer-based delay loop\n");
        delay_timer         = timer;
        lpj_fine            = timer->freq / HZ;
        loops_per_jiffy         = lpj_fine;
        arm_delay_ops.delay     = __timer_delay;
        arm_delay_ops.const_udelay  = __timer_const_udelay;
        arm_delay_ops.udelay        = __timer_udelay;
        delay_calibrated        = true;
    } else {
        pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
    }
}

unsigned long __cpuinit calibrate_delay_is_known(void)
{
    delay_calibrated = true;
    return lpj_fine;
}