arch/x86/kernel/tsc_msr.c

   1 /*
   2  * tsc_msr.c - MSR based TSC calibration on Intel Atom SoC platforms.
   3  *
   4  * TSC in Intel Atom SoC runs at a constant rate which can be figured
   5  * by this formula:
   6  * <maximum core-clock to bus-clock ratio> * <maximum resolved frequency>
   7  * See Intel 64 and IA-32 System Programming Guid section 16.12 and 30.11.5
   8  * for details.
   9  * Especially some Intel Atom SoCs don't have PIT(i8254) or HPET, so MSR
  10  * based calibration is the only option.
  11  *
  12  *
  13  * Copyright (C) 2013 Intel Corporation
  14  * Author: Bin Gao <bin.gao@intel.com>
  15  *
  16  * This file is released under the GPLv2.
  17  */
  18
  19 #include <linux/kernel.h>
  20 #include <asm/processor.h>
  21 #include <asm/setup.h>
  22 #include <asm/apic.h>
  23 #include <asm/param.h>
  24
  25 /* CPU reference clock frequency: in KHz */
  26 #define FREQ_83         83200
  27 #define FREQ_100        99840
  28 #define FREQ_133        133200
  29 #define FREQ_166        166400
  30
  31 #define MAX_NUM_FREQS   8
  32
  33 /*
  34  * According to Intel 64 and IA-32 System Programming Guide,
  35  * if MSR_PERF_STAT[31] is set, the maximum resolved bus ratio can be
  36  * read in MSR_PLATFORM_ID[12:8], otherwise in MSR_PERF_STAT[44:40].
  37  * Unfortunately some Intel Atom SoCs aren't quite compliant to this,
  38  * so we need manually differentiate SoC families. This is what the
  39  * field msr_plat does.
  40  */
  41 struct freq_desc {
  42         u8 x86_family;  /* CPU family */
  43         u8 x86_model;   /* model */
  44         u8 msr_plat;    /* 1: use MSR_PLATFORM_INFO, 0: MSR_IA32_PERF_STATUS */
  45         u32 freqs[MAX_NUM_FREQS];
  46 };
  47
  48 static struct freq_desc freq_desc_tables[] = {
  49         /* PNW */
  50         { 6, 0x27, 0, { 0, 0, 0, 0, 0, FREQ_100, 0, FREQ_83 } },
  51         /* CLV+ */
  52         { 6, 0x35, 0, { 0, FREQ_133, 0, 0, 0, FREQ_100, 0, FREQ_83 } },
  53         /* TNG */
  54         { 6, 0x4a, 1, { 0, FREQ_100, FREQ_133, 0, 0, 0, 0, 0 } },
  55         /* VLV2 */
  56         { 6, 0x37, 1, { FREQ_83, FREQ_100, FREQ_133, FREQ_166, 0, 0, 0, 0 } },
  57         /* ANN */
  58         { 6, 0x5a, 1, { FREQ_83, FREQ_100, FREQ_133, FREQ_100, 0, 0, 0, 0 } },
  59 };
  60
  61 static int match_cpu(u8 family, u8 model)
  62 {
  63         int i;
  64
  65         for (i = 0; i < ARRAY_SIZE(freq_desc_tables); i++) {
  66                 if ((family == freq_desc_tables[i].x86_family) &&
  67                         (model == freq_desc_tables[i].x86_model))
  68                         return i;
  69         }
  70
  71         return -1;
  72 }
  73
  74 /* Map CPU reference clock freq ID(0-7) to CPU reference clock freq(KHz) */
  75 #define id_to_freq(cpu_index, freq_id) \
  76         (freq_desc_tables[cpu_index].freqs[freq_id])
  77
  78 /*
  79  * Do MSR calibration only for known/supported CPUs.
  80  *
  81  * Returns the calibration value or 0 if MSR calibration failed.
  82  */
  83 unsigned long try_msr_calibrate_tsc(void)
  84 {
  85         u32 lo, hi, ratio, freq_id, freq;
  86         unsigned long res;
  87         int cpu_index;
  88
  89         cpu_index = match_cpu(boot_cpu_data.x86, boot_cpu_data.x86_model);
  90         if (cpu_index < 0)
  91                 return 0;
  92
  93         if (freq_desc_tables[cpu_index].msr_plat) {
  94                 rdmsr(MSR_PLATFORM_INFO, lo, hi);
  95                 ratio = (lo >> 8) & 0xff;
  96         } else {
  97                 rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
  98                 ratio = (hi >> 8) & 0x1f;
  99         }
 100         pr_info("Maximum core-clock to bus-clock ratio: 0x%x\n", ratio);
 101
 102         if (!ratio)
 103                 goto fail;
 104
 105         /* Get FSB FREQ ID */
 106         rdmsr(MSR_FSB_FREQ, lo, hi);
 107         freq_id = lo & 0x7;
 108         freq = id_to_freq(cpu_index, freq_id);
 109         pr_info("Resolved frequency ID: %u, frequency: %u KHz\n",
 110                                 freq_id, freq);
 111         if (!freq)
 112                 goto fail;
 113
 114         /* TSC frequency = maximum resolved freq * maximum resolved bus ratio */
 115         res = freq * ratio;
 116         pr_info("TSC runs at %lu KHz\n", res);
 117
 118 #ifdef CONFIG_X86_LOCAL_APIC
 119         lapic_timer_frequency = (freq * 1000) / HZ;
 120         pr_info("lapic_timer_frequency = %d\n", lapic_timer_frequency);
 121 #endif
 122         return res;
 123
 124 fail:
 125         pr_warn("Fast TSC calibration using MSR failed\n");
 126         return 0;
 127 }