payloads/libpayload/arch/x86/timer.c

   1 /*
   2  *
   3  * Copyright (C) 2008 Advanced Micro Devices, Inc.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. The name of the author may not be used to endorse or promote products
  14  *    derived from this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  26  * SUCH DAMAGE.
  27  */
  28
  29 /**
  30  * @file x86/timer.c
  31  * x86 specific timer routines
  32  */
  33
  34 #include <libpayload.h>
  35 #include <arch/rdtsc.h>
  36 #include <arch/cpuid.h>
  37 #include <arch/msr.h>
  38
  39 #define MSR_PLATFORM_INFO               0xce
  40
  41 /**
  42  * @ingroup arch
  43  * Global variable containing the speed of the processor in KHz.
  44  */
  45 uint32_t cpu_khz;
  46
  47 /**
  48  * @brief Measure the speed of the processor for use in delays
  49  *
  50  * @return The CPU speed in kHz.
  51  */
  52 static unsigned int calibrate_pit(void)
  53 {
  54         unsigned long long start, end;
  55         const uint32_t clock_rate = 1193182; // 1.193182 MHz
  56         const uint16_t interval = (2 * clock_rate) / 1000; // 2 ms
  57
  58         /* Set up the PPC port - disable the speaker, enable the T2 gate. */
  59         outb((inb(0x61) & ~0x02) | 0x01, 0x61);
  60
  61         /* Set the PIT to Mode 0, counter 2, word access. */
  62         outb(0xB0, 0x43);
  63
  64         /* Load the interval into the counter. */
  65         outb(interval & 0xff, 0x42);
  66         outb((interval >> 8) & 0xff, 0x42);
  67
  68         /* Read the number of ticks during the period. */
  69         start = rdtsc();
  70         while (!(inb(0x61) & 0x20)) ;
  71         end = rdtsc();
  72
  73         /*
  74          * The number of milliseconds for a period is
  75          * clock_rate / (interval * 1000). Multiply that by the number of
  76          * measured clocks to get the kHz value.
  77          */
  78         return (end - start) * clock_rate / (1000 * interval);
  79 }
  80
  81 /**
  82  * @brief Calculates the core clock frequency via CPUID 0x15
  83  *
  84  * Newer Intel CPUs report their core clock in CPUID leaf 0x15. Early models
  85  * supporting this leaf didn't provide the nominal crystal frequency in ecx,
  86  * hence we use hard coded values for them.
  87  */
  88 static int get_cpu_khz_xtal(void)
  89 {
  90         uint32_t ecx, edx, num, denom;
  91         uint64_t nominal;
  92
  93         if (cpuid_max() < 0x15)
  94                 return -1;
  95         cpuid(0x15, denom, num, ecx, edx);
  96
  97         if (denom == 0 || num == 0)
  98                 return -1;
  99
 100         if (ecx != 0) {
 101                 nominal = ecx;
 102         } else {
 103                 if (cpuid_family() != 6)
 104                         return -1;
 105
 106                 switch (cpuid_model()) {
 107                 case SKYLAKE_U_Y:
 108                 case SKYLAKE_S_H:
 109                 case KABYLAKE_U_Y:
 110                 case KABYLAKE_S_H:
 111                         nominal = 24000000;
 112                         break;
 113                 case APOLLOLAKE:
 114                         nominal = 19200000;
 115                         break;
 116                 default:
 117                         return -1;
 118                 }
 119         }
 120
 121         return nominal * num / denom / 1000;
 122 }
 123
 124 /**
 125  * @brief Returns three times the bus clock in kHz
 126  *
 127  * The result of calculations with the returned value shall be divided by 3.
 128  * This helps to avoid rounding errors.
 129  */
 130 static int get_bus_khz_x3(void)
 131 {
 132         if (cpuid_family() != 6)
 133                 return -1;
 134
 135         switch (cpuid_model()) {
 136         case NEHALEM:
 137                 return 400 * 1000; /* 133 MHz */
 138         case SANDYBRIDGE:
 139         case IVYBRIDGE:
 140         case HASWELL:
 141         case HASWELL_U:
 142         case HASWELL_GT3E:
 143         case BROADWELL:
 144         case BROADWELL_U:
 145                 return 300 * 1000; /* 100 MHz */
 146         default:
 147                 return -1;
 148         }
 149 }
 150
 151 /**
 152  * @brief Returns the calculated CPU frequency
 153  *
 154  * Over the years, multiple ways to discover the CPU frequency have been
 155  * exposed through CPUID and MSRs. Try the most recent and accurate first
 156  * (crystal information in CPUID leaf 0x15) and then fall back to older
 157  * methods.
 158  *
 159  * This should cover all Intel Core i processors at least. For older
 160  * processors we fall back to the PIT calibration.
 161  */
 162 static int get_cpu_khz_fast(void)
 163 {
 164         /* Try core crystal clock frequency first (supposed to be more accurate). */
 165         const int cpu_khz_xtal = get_cpu_khz_xtal();
 166         if (cpu_khz_xtal > 0)
 167                 return cpu_khz_xtal;
 168
 169         /* Try `bus clock * speedstep multiplier`. */
 170         const int bus_x3 = get_bus_khz_x3();
 171         if (bus_x3 <= 0)
 172                 return -1;
 173         /*
 174          * Systems with an invariant TSC report the multiplier (maximum
 175          * non-turbo ratio) in MSR_PLATFORM_INFO[15:8].
 176          */
 177         const unsigned int mult = _rdmsr(MSR_PLATFORM_INFO) >> 8 & 0xff;
 178         return bus_x3 * mult / 3;
 179 }
 180
 181 unsigned int get_cpu_speed(void)
 182 {
 183         const int cpu_khz_fast = get_cpu_khz_fast();
 184         if (cpu_khz_fast > 0)
 185                 cpu_khz = (unsigned int)cpu_khz_fast;
 186         else
 187                 cpu_khz = calibrate_pit();
 188
 189         return cpu_khz;
 190 }