root/arch/x86/lib/delay.c

DEFINITIONS

1. delay_loop
2. delay_tsc
3. use_tsc_delay
4. read_current_timer
5. __delay
6. __const_udelay
7. __udelay
8. __ndelay

/*
 *      Precise Delay Loops for i386
 *
 *      Copyright (C) 1993 Linus Torvalds
 *      Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
 *      Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
 *
 *      The __delay function must _NOT_ be inlined as its execution time
 *      depends wildly on alignment on many x86 processors. The additional
 *      jump magic is needed to get the timing stable on all the CPU's
 *      we have to worry about.
 */

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

#include <asm/processor.h>
#include <asm/delay.h>
#include <asm/timer.h>

#ifdef CONFIG_SMP
# include <asm/smp.h>
#endif

/* simple loop based delay: */
static void delay_loop(unsigned long loops)
{
        asm volatile(
                "       test %0,%0      \n"
                "       jz 3f           \n"
                "       jmp 1f          \n"

                ".align 16              \n"
                "1:     jmp 2f          \n"

                ".align 16              \n"
                "2:     dec %0          \n"
                "       jnz 2b          \n"
                "3:     dec %0          \n"

                : /* we don't need output */
                :"a" (loops)
        );
}

/* TSC based delay: */
static void delay_tsc(unsigned long loops)
{
        unsigned long bclock, now;
        int cpu;

        preempt_disable();
        cpu = smp_processor_id();
        rdtscl(bclock);
        for (;;) {
                rdtscl(now);
                if ((now - bclock) >= loops)
                        break;

                /* Allow RT tasks to run */
                preempt_enable();
                rep_nop();
                preempt_disable();

                /*
                 * It is possible that we moved to another CPU, and
                 * since TSC's are per-cpu we need to calculate
                 * that. The delay must guarantee that we wait "at
                 * least" the amount of time. Being moved to another
                 * CPU could make the wait longer but we just need to
                 * make sure we waited long enough. Rebalance the
                 * counter for this CPU.
                 */
                if (unlikely(cpu != smp_processor_id())) {
                        loops -= (now - bclock);
                        cpu = smp_processor_id();
                        rdtscl(bclock);
                }
        }
        preempt_enable();
}

/*
 * Since we calibrate only once at boot, this
 * function should be set once at boot and not changed
 */
static void (*delay_fn)(unsigned long) = delay_loop;

void use_tsc_delay(void)
{
        delay_fn = delay_tsc;
}

int __devinit read_current_timer(unsigned long *timer_val)
{
        if (delay_fn == delay_tsc) {
                rdtscll(*timer_val);
                return 0;
        }
        return -1;
}

void __delay(unsigned long loops)
{
        delay_fn(loops);
}
EXPORT_SYMBOL(__delay);

inline void __const_udelay(unsigned long xloops)
{
        int d0;

        xloops *= 4;
        asm("mull %%edx"
                :"=d" (xloops), "=&a" (d0)
                :"1" (xloops), "0"
                (cpu_data(raw_smp_processor_id()).loops_per_jiffy * (HZ/4)));

        __delay(++xloops);
}
EXPORT_SYMBOL(__const_udelay);

void __udelay(unsigned long usecs)
{
        __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
}
EXPORT_SYMBOL(__udelay);

void __ndelay(unsigned long nsecs)
{
        __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
}
EXPORT_SYMBOL(__ndelay);