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