arch/i386/kernel/timers/common.c

   1 /*
   2  *      Common functions used across the timers go here
   3  */
   4
   5 #include <linux/init.h>
   6 #include <linux/timex.h>
   7 #include <linux/errno.h>
   8 #include <linux/jiffies.h>
   9 #include <linux/module.h>
  10
  11 #include <asm/io.h>
  12 #include <asm/timer.h>
  13 #include <asm/hpet.h>
  14
  15 #include "mach_timer.h"
  16
  17 /* ------ Calibrate the TSC -------
  18  * Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
  19  * Too much 64-bit arithmetic here to do this cleanly in C, and for
  20  * accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
  21  * output busy loop as low as possible. We avoid reading the CTC registers
  22  * directly because of the awkward 8-bit access mechanism of the 82C54
  23  * device.
  24  */
  25
  26 #define CALIBRATE_TIME  (5 * 1000020/HZ)
  27
  28 unsigned long calibrate_tsc(void)
  29 {
  30         mach_prepare_counter();
  31
  32         {
  33                 unsigned long startlow, starthigh;
  34                 unsigned long endlow, endhigh;
  35                 unsigned long count;
  36
  37                 rdtsc(startlow,starthigh);
  38                 mach_countup(&count);
  39                 rdtsc(endlow,endhigh);
  40
  41
  42                 /* Error: ECTCNEVERSET */
  43                 if (count <= 1)
  44                         goto bad_ctc;
  45
  46                 /* 64-bit subtract - gcc just messes up with long longs */
  47                 __asm__("subl %2,%0\n\t"
  48                         "sbbl %3,%1"
  49                         :"=a" (endlow), "=d" (endhigh)
  50                         :"g" (startlow), "g" (starthigh),
  51                          "0" (endlow), "1" (endhigh));
  52
  53                 /* Error: ECPUTOOFAST */
  54                 if (endhigh)
  55                         goto bad_ctc;
  56
  57                 /* Error: ECPUTOOSLOW */
  58                 if (endlow <= CALIBRATE_TIME)
  59                         goto bad_ctc;
  60
  61                 __asm__("divl %2"
  62                         :"=a" (endlow), "=d" (endhigh)
  63                         :"r" (endlow), "0" (0), "1" (CALIBRATE_TIME));
  64
  65                 return endlow;
  66         }
  67
  68         /*
  69          * The CTC wasn't reliable: we got a hit on the very first read,
  70          * or the CPU was so fast/slow that the quotient wouldn't fit in
  71          * 32 bits..
  72          */
  73 bad_ctc:
  74         return 0;
  75 }
  76
  77 #ifdef CONFIG_HPET_TIMER
  78 /* ------ Calibrate the TSC using HPET -------
  79  * Return 2^32 * (1 / (TSC clocks per usec)) for getting the CPU freq.
  80  * Second output is parameter 1 (when non NULL)
  81  * Set 2^32 * (1 / (tsc per HPET clk)) for delay_hpet().
  82  * calibrate_tsc() calibrates the processor TSC by comparing
  83  * it to the HPET timer of known frequency.
  84  * Too much 64-bit arithmetic here to do this cleanly in C
  85  */
  86 #define CALIBRATE_CNT_HPET      (5 * hpet_tick)
  87 #define CALIBRATE_TIME_HPET     (5 * KERNEL_TICK_USEC)
  88
  89 unsigned long __devinit calibrate_tsc_hpet(unsigned long *tsc_hpet_quotient_ptr)
  90 {
  91         unsigned long tsc_startlow, tsc_starthigh;
  92         unsigned long tsc_endlow, tsc_endhigh;
  93         unsigned long hpet_start, hpet_end;
  94         unsigned long result, remain;
  95
  96         hpet_start = hpet_readl(HPET_COUNTER);
  97         rdtsc(tsc_startlow, tsc_starthigh);
  98         do {
  99                 hpet_end = hpet_readl(HPET_COUNTER);
 100         } while ((hpet_end - hpet_start) < CALIBRATE_CNT_HPET);
 101         rdtsc(tsc_endlow, tsc_endhigh);
 102
 103         /* 64-bit subtract - gcc just messes up with long longs */
 104         __asm__("subl %2,%0\n\t"
 105                 "sbbl %3,%1"
 106                 :"=a" (tsc_endlow), "=d" (tsc_endhigh)
 107                 :"g" (tsc_startlow), "g" (tsc_starthigh),
 108                  "0" (tsc_endlow), "1" (tsc_endhigh));
 109
 110         /* Error: ECPUTOOFAST */
 111         if (tsc_endhigh)
 112                 goto bad_calibration;
 113
 114         /* Error: ECPUTOOSLOW */
 115         if (tsc_endlow <= CALIBRATE_TIME_HPET)
 116                 goto bad_calibration;
 117
 118         ASM_DIV64_REG(result, remain, tsc_endlow, 0, CALIBRATE_TIME_HPET);
 119         if (remain > (tsc_endlow >> 1))
 120                 result++; /* rounding the result */
 121
 122         if (tsc_hpet_quotient_ptr) {
 123                 unsigned long tsc_hpet_quotient;
 124
 125                 ASM_DIV64_REG(tsc_hpet_quotient, remain, tsc_endlow, 0,
 126                         CALIBRATE_CNT_HPET);
 127                 if (remain > (tsc_endlow >> 1))
 128                         tsc_hpet_quotient++; /* rounding the result */
 129                 *tsc_hpet_quotient_ptr = tsc_hpet_quotient;
 130         }
 131
 132         return result;
 133 bad_calibration:
 134         /*
 135          * the CPU was so fast/slow that the quotient wouldn't fit in
 136          * 32 bits..
 137          */
 138         return 0;
 139 }
 140 #endif
 141
 142
 143 unsigned long read_timer_tsc(void)
 144 {
 145         unsigned long retval;
 146         rdtscl(retval);
 147         return retval;
 148 }
 149
 150
 151 /* calculate cpu_khz */
 152 void init_cpu_khz(void)
 153 {
 154         if (cpu_has_tsc) {
 155                 unsigned long tsc_quotient = calibrate_tsc();
 156                 if (tsc_quotient) {
 157                         /* report CPU clock rate in Hz.
 158                          * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
 159                          * clock/second. Our precision is about 100 ppm.
 160                          */
 161                         {       unsigned long eax=0, edx=1000;
 162                                 __asm__("divl %2"
 163                                 :"=a" (cpu_khz), "=d" (edx)
 164                                 :"r" (tsc_quotient),
 165                                 "0" (eax), "1" (edx));
 166                                 printk("Detected %u.%03u MHz processor.\n",
 167                                         cpu_khz / 1000, cpu_khz % 1000);
 168                         }
 169                 }
 170         }
 171 }
 172