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tsc_32.c

#include <linux/sched.h>
#include <linux/clocksource.h>
#include <linux/workqueue.h>
#include <linux/cpufreq.h>
#include <linux/jiffies.h>
#include <linux/init.h>
#include <linux/dmi.h>

#include <asm/delay.h>
#include <asm/tsc.h>
#include <asm/io.h>
#include <asm/timer.h>

#include "mach_timer.h"

static int tsc_enabled;

/*
 * On some systems the TSC frequency does not
 * change with the cpu frequency. So we need
 * an extra value to store the TSC freq
 */
unsigned int tsc_khz;
EXPORT_SYMBOL_GPL(tsc_khz);

int tsc_disable;

#ifdef CONFIG_X86_TSC
static int __init tsc_setup(char *str)
{
      printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
                        "cannot disable TSC.\n");
      return 1;
}
#else
/*
 * disable flag for tsc. Takes effect by clearing the TSC cpu flag
 * in cpu/common.c
 */
static int __init tsc_setup(char *str)
{
      tsc_disable = 1;

      return 1;
}
#endif

__setup("notsc", tsc_setup);

/*
 * code to mark and check if the TSC is unstable
 * due to cpufreq or due to unsynced TSCs
 */
static int tsc_unstable;

int check_tsc_unstable(void)
{
      return tsc_unstable;
}
EXPORT_SYMBOL_GPL(check_tsc_unstable);

/* Accelerators for sched_clock()
 * convert from cycles(64bits) => nanoseconds (64bits)
 *  basic equation:
 *          ns = cycles / (freq / ns_per_sec)
 *          ns = cycles * (ns_per_sec / freq)
 *          ns = cycles * (10^9 / (cpu_khz * 10^3))
 *          ns = cycles * (10^6 / cpu_khz)
 *
 *    Then we use scaling math (suggested by george@mvista.com) to get:
 *          ns = cycles * (10^6 * SC / cpu_khz) / SC
 *          ns = cycles * cyc2ns_scale / SC
 *
 *    And since SC is a constant power of two, we can convert the div
 *  into a shift.
 *
 *  We can use khz divisor instead of mhz to keep a better precision, since
 *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
 *  (mathieu.desnoyers@polymtl.ca)
 *
 *                -johnstul@us.ibm.com "math is hard, lets go shopping!"
 */
unsigned long cyc2ns_scale __read_mostly;

#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */

static inline void set_cyc2ns_scale(unsigned long cpu_khz)
{
      cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
}

/*
 * Scheduler clock - returns current time in nanosec units.
 */
unsigned long long native_sched_clock(void)
{
      unsigned long long this_offset;

      /*
       * Fall back to jiffies if there's no TSC available:
       * ( But note that we still use it if the TSC is marked
       *   unstable. We do this because unlike Time Of Day,
       *   the scheduler clock tolerates small errors and it's
       *   very important for it to be as fast as the platform
       *   can achive it. )
       */
      if (unlikely(!tsc_enabled && !tsc_unstable))
            /* No locking but a rare wrong value is not a big deal: */
            return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);

      /* read the Time Stamp Counter: */
      rdtscll(this_offset);

      /* return the value in ns */
      return cycles_2_ns(this_offset);
}

/* We need to define a real function for sched_clock, to override the
   weak default version */
#ifdef CONFIG_PARAVIRT
unsigned long long sched_clock(void)
{
      return paravirt_sched_clock();
}
#else
unsigned long long sched_clock(void)
      __attribute__((alias("native_sched_clock")));
#endif

unsigned long native_calculate_cpu_khz(void)
{
      unsigned long long start, end;
      unsigned long count;
      u64 delta64 = (u64)ULLONG_MAX;
      int i;
      unsigned long flags;

      local_irq_save(flags);

      /* run 3 times to ensure the cache is warm and to get an accurate reading */
      for (i = 0; i < 3; i++) {
            mach_prepare_counter();
            rdtscll(start);
            mach_countup(&count);
            rdtscll(end);

            /*
             * Error: ECTCNEVERSET
             * The CTC wasn't reliable: we got a hit on the very first read,
             * or the CPU was so fast/slow that the quotient wouldn't fit in
             * 32 bits..
             */
            if (count <= 1)
                  continue;

            /* cpu freq too slow: */
            if ((end - start) <= CALIBRATE_TIME_MSEC)
                  continue;

            /*
             * We want the minimum time of all runs in case one of them
             * is inaccurate due to SMI or other delay
             */
            delta64 = min(delta64, (end - start));
      }

      /* cpu freq too fast (or every run was bad): */
      if (delta64 > (1ULL<<32))
            goto err;

      delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
      do_div(delta64,CALIBRATE_TIME_MSEC);

      local_irq_restore(flags);
      return (unsigned long)delta64;
err:
      local_irq_restore(flags);
      return 0;
}

int recalibrate_cpu_khz(void)
{
#ifndef CONFIG_SMP
      unsigned long cpu_khz_old = cpu_khz;

      if (cpu_has_tsc) {
            cpu_khz = calculate_cpu_khz();
            tsc_khz = cpu_khz;
            cpu_data(0).loops_per_jiffy =
                  cpufreq_scale(cpu_data(0).loops_per_jiffy,
                              cpu_khz_old, cpu_khz);
            return 0;
      } else
            return -ENODEV;
#else
      return -ENODEV;
#endif
}

EXPORT_SYMBOL(recalibrate_cpu_khz);

#ifdef CONFIG_CPU_FREQ

/*
 * if the CPU frequency is scaled, TSC-based delays will need a different
 * loops_per_jiffy value to function properly.
 */
static unsigned int ref_freq = 0;
static unsigned long loops_per_jiffy_ref = 0;
static unsigned long cpu_khz_ref = 0;

static int
time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
{
      struct cpufreq_freqs *freq = data;

      if (!ref_freq) {
            if (!freq->old){
                  ref_freq = freq->new;
                  return 0;
            }
            ref_freq = freq->old;
            loops_per_jiffy_ref = cpu_data(freq->cpu).loops_per_jiffy;
            cpu_khz_ref = cpu_khz;
      }

      if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
          (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
          (val == CPUFREQ_RESUMECHANGE)) {
            if (!(freq->flags & CPUFREQ_CONST_LOOPS))
                  cpu_data(freq->cpu).loops_per_jiffy =
                        cpufreq_scale(loops_per_jiffy_ref,
                                    ref_freq, freq->new);

            if (cpu_khz) {

                  if (num_online_cpus() == 1)
                        cpu_khz = cpufreq_scale(cpu_khz_ref,
                                    ref_freq, freq->new);
                  if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
                        tsc_khz = cpu_khz;
                        set_cyc2ns_scale(cpu_khz);
                        /*
                         * TSC based sched_clock turns
                         * to junk w/ cpufreq
                         */
                        mark_tsc_unstable("cpufreq changes");
                  }
            }
      }

      return 0;
}

static struct notifier_block time_cpufreq_notifier_block = {
      .notifier_call    = time_cpufreq_notifier
};

static int __init cpufreq_tsc(void)
{
      return cpufreq_register_notifier(&time_cpufreq_notifier_block,
                               CPUFREQ_TRANSITION_NOTIFIER);
}
core_initcall(cpufreq_tsc);

#endif

/* clock source code */

static unsigned long current_tsc_khz = 0;

static cycle_t read_tsc(void)
{
      cycle_t ret;

      rdtscll(ret);

      return ret;
}

static struct clocksource clocksource_tsc = {
      .name             = "tsc",
      .rating                 = 300,
      .read             = read_tsc,
      .mask             = CLOCKSOURCE_MASK(64),
      .mult             = 0, /* to be set */
      .shift                  = 22,
      .flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
                          CLOCK_SOURCE_MUST_VERIFY,
};

void mark_tsc_unstable(char *reason)
{
      if (!tsc_unstable) {
            tsc_unstable = 1;
            tsc_enabled = 0;
            printk("Marking TSC unstable due to: %s.\n", reason);
            /* Can be called before registration */
            if (clocksource_tsc.mult)
                  clocksource_change_rating(&clocksource_tsc, 0);
            else
                  clocksource_tsc.rating = 0;
      }
}
EXPORT_SYMBOL_GPL(mark_tsc_unstable);

static int __init dmi_mark_tsc_unstable(const struct dmi_system_id *d)
{
      printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
                   d->ident);
      tsc_unstable = 1;
      return 0;
}

/* List of systems that have known TSC problems */
static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
      {
       .callback = dmi_mark_tsc_unstable,
       .ident = "IBM Thinkpad 380XD",
       .matches = {
                 DMI_MATCH(DMI_BOARD_VENDOR, "IBM"),
                 DMI_MATCH(DMI_BOARD_NAME, "2635FA0"),
                 },
       },
       {}
};

/*
 * Make an educated guess if the TSC is trustworthy and synchronized
 * over all CPUs.
 */
__cpuinit int unsynchronized_tsc(void)
{
      if (!cpu_has_tsc || tsc_unstable)
            return 1;
      /*
       * Intel systems are normally all synchronized.
       * Exceptions must mark TSC as unstable:
       */
      if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
            /* assume multi socket systems are not synchronized: */
            if (num_possible_cpus() > 1)
                  tsc_unstable = 1;
      }
      return tsc_unstable;
}

/*
 * Geode_LX - the OLPC CPU has a possibly a very reliable TSC
 */
#ifdef CONFIG_MGEODE_LX
/* RTSC counts during suspend */
#define RTSC_SUSP 0x100

static void __init check_geode_tsc_reliable(void)
{
      unsigned long res_low, res_high;

      rdmsr_safe(MSR_GEODE_BUSCONT_CONF0, &res_low, &res_high);
      if (res_low & RTSC_SUSP)
            clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
}
#else
static inline void check_geode_tsc_reliable(void) { }
#endif


void __init tsc_init(void)
{
      if (!cpu_has_tsc || tsc_disable)
            goto out_no_tsc;

      cpu_khz = calculate_cpu_khz();
      tsc_khz = cpu_khz;

      if (!cpu_khz)
            goto out_no_tsc;

      printk("Detected %lu.%03lu MHz processor.\n",
                        (unsigned long)cpu_khz / 1000,
                        (unsigned long)cpu_khz % 1000);

      set_cyc2ns_scale(cpu_khz);
      use_tsc_delay();

      /* Check and install the TSC clocksource */
      dmi_check_system(bad_tsc_dmi_table);

      unsynchronized_tsc();
      check_geode_tsc_reliable();
      current_tsc_khz = tsc_khz;
      clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
                                          clocksource_tsc.shift);
      /* lower the rating if we already know its unstable: */
      if (check_tsc_unstable()) {
            clocksource_tsc.rating = 0;
            clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
      } else
            tsc_enabled = 1;

      clocksource_register(&clocksource_tsc);

      return;

out_no_tsc:
      /*
       * Set the tsc_disable flag if there's no TSC support, this
       * makes it a fast flag for the kernel to see whether it
       * should be using the TSC.
       */
      tsc_disable = 1;
}

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