arch/x86/kernel/tsc_msr.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * TSC frequency enumeration via MSR
   4  *
   5  * Copyright (C) 2013, 2018 Intel Corporation
   6  * Author: Bin Gao <bin.gao@intel.com>
   7  */
   8
   9 #include <linux/kernel.h>
  10 #include <linux/thread_info.h>
  11
  12 #include <asm/apic.h>
  13 #include <asm/cpu_device_id.h>
  14 #include <asm/intel-family.h>
  15 #include <asm/msr.h>
  16 #include <asm/param.h>
  17 #include <asm/tsc.h>
  18
  19 #define MAX_NUM_FREQS   16 /* 4 bits to select the frequency */
  20
  21 /*
  22  * The frequency numbers in the SDM are e.g. 83.3 MHz, which does not contain a
  23  * lot of accuracy which leads to clock drift. As far as we know Bay Trail SoCs
  24  * use a 25 MHz crystal and Cherry Trail uses a 19.2 MHz crystal, the crystal
  25  * is the source clk for a root PLL which outputs 1600 and 100 MHz. It is
  26  * unclear if the root PLL outputs are used directly by the CPU clock PLL or
  27  * if there is another PLL in between.
  28  * This does not matter though, we can model the chain of PLLs as a single PLL
  29  * with a quotient equal to the quotients of all PLLs in the chain multiplied.
  30  * So we can create a simplified model of the CPU clock setup using a reference
  31  * clock of 100 MHz plus a quotient which gets us as close to the frequency
  32  * from the SDM as possible.
  33  * For the 83.3 MHz example from above this would give us 100 MHz * 5 / 6 =
  34  * 83 and 1/3 MHz, which matches exactly what has been measured on actual hw.
  35  */
  36 #define TSC_REFERENCE_KHZ 100000
  37
  38 struct muldiv {
  39         u32 multiplier;
  40         u32 divider;
  41 };
  42
  43 /*
  44  * If MSR_PERF_STAT[31] is set, the maximum resolved bus ratio can be
  45  * read in MSR_PLATFORM_ID[12:8], otherwise in MSR_PERF_STAT[44:40].
  46  * Unfortunately some Intel Atom SoCs aren't quite compliant to this,
  47  * so we need manually differentiate SoC families. This is what the
  48  * field use_msr_plat does.
  49  */
  50 struct freq_desc {
  51         bool use_msr_plat;
  52         struct muldiv muldiv[MAX_NUM_FREQS];
  53         /*
  54          * Some CPU frequencies in the SDM do not map to known PLL freqs, in
  55          * that case the muldiv array is empty and the freqs array is used.
  56          */
  57         u32 freqs[MAX_NUM_FREQS];
  58         u32 mask;
  59 };
  60
  61 /*
  62  * Penwell and Clovertrail use spread spectrum clock,
  63  * so the freq number is not exactly the same as reported
  64  * by MSR based on SDM.
  65  */
  66 static const struct freq_desc freq_desc_pnw = {
  67         .use_msr_plat = false,
  68         .freqs = { 0, 0, 0, 0, 0, 99840, 0, 83200 },
  69         .mask = 0x07,
  70 };
  71
  72 static const struct freq_desc freq_desc_clv = {
  73         .use_msr_plat = false,
  74         .freqs = { 0, 133200, 0, 0, 0, 99840, 0, 83200 },
  75         .mask = 0x07,
  76 };
  77
  78 /*
  79  * Bay Trail SDM MSR_FSB_FREQ frequencies simplified PLL model:
  80  *  000:   100 *  5 /  6  =  83.3333 MHz
  81  *  001:   100 *  1 /  1  = 100.0000 MHz
  82  *  010:   100 *  4 /  3  = 133.3333 MHz
  83  *  011:   100 *  7 /  6  = 116.6667 MHz
  84  *  100:   100 *  4 /  5  =  80.0000 MHz
  85  */
  86 static const struct freq_desc freq_desc_byt = {
  87         .use_msr_plat = true,
  88         .muldiv = { { 5, 6 }, { 1, 1 }, { 4, 3 }, { 7, 6 },
  89                     { 4, 5 } },
  90         .mask = 0x07,
  91 };
  92
  93 /*
  94  * Cherry Trail SDM MSR_FSB_FREQ frequencies simplified PLL model:
  95  * 0000:   100 *  5 /  6  =  83.3333 MHz
  96  * 0001:   100 *  1 /  1  = 100.0000 MHz
  97  * 0010:   100 *  4 /  3  = 133.3333 MHz
  98  * 0011:   100 *  7 /  6  = 116.6667 MHz
  99  * 0100:   100 *  4 /  5  =  80.0000 MHz
 100  * 0101:   100 * 14 / 15  =  93.3333 MHz
 101  * 0110:   100 *  9 / 10  =  90.0000 MHz
 102  * 0111:   100 *  8 /  9  =  88.8889 MHz
 103  * 1000:   100 *  7 /  8  =  87.5000 MHz
 104  */
 105 static const struct freq_desc freq_desc_cht = {
 106         .use_msr_plat = true,
 107         .muldiv = { { 5, 6 }, {  1,  1 }, { 4,  3 }, { 7, 6 },
 108                     { 4, 5 }, { 14, 15 }, { 9, 10 }, { 8, 9 },
 109                     { 7, 8 } },
 110         .mask = 0x0f,
 111 };
 112
 113 /*
 114  * Merriefield SDM MSR_FSB_FREQ frequencies simplified PLL model:
 115  * 0001:   100 *  1 /  1  = 100.0000 MHz
 116  * 0010:   100 *  4 /  3  = 133.3333 MHz
 117  */
 118 static const struct freq_desc freq_desc_tng = {
 119         .use_msr_plat = true,
 120         .muldiv = { { 0, 0 }, { 1, 1 }, { 4, 3 } },
 121         .mask = 0x07,
 122 };
 123
 124 /*
 125  * Moorefield SDM MSR_FSB_FREQ frequencies simplified PLL model:
 126  * 0000:   100 *  5 /  6  =  83.3333 MHz
 127  * 0001:   100 *  1 /  1  = 100.0000 MHz
 128  * 0010:   100 *  4 /  3  = 133.3333 MHz
 129  * 0011:   100 *  1 /  1  = 100.0000 MHz
 130  */
 131 static const struct freq_desc freq_desc_ann = {
 132         .use_msr_plat = true,
 133         .muldiv = { { 5, 6 }, { 1, 1 }, { 4, 3 }, { 1, 1 } },
 134         .mask = 0x0f,
 135 };
 136
 137 /*
 138  * 24 MHz crystal? : 24 * 13 / 4 = 78 MHz
 139  * Frequency step for Lightning Mountain SoC is fixed to 78 MHz,
 140  * so all the frequency entries are 78000.
 141  */
 142 static const struct freq_desc freq_desc_lgm = {
 143         .use_msr_plat = true,
 144         .freqs = { 78000, 78000, 78000, 78000, 78000, 78000, 78000, 78000,
 145                    78000, 78000, 78000, 78000, 78000, 78000, 78000, 78000 },
 146         .mask = 0x0f,
 147 };
 148
 149 static const struct x86_cpu_id tsc_msr_cpu_ids[] = {
 150         X86_MATCH_VFM(INTEL_ATOM_SALTWELL_MID,  &freq_desc_pnw),
 151         X86_MATCH_VFM(INTEL_ATOM_SALTWELL_TABLET, &freq_desc_clv),
 152         X86_MATCH_VFM(INTEL_ATOM_SILVERMONT,    &freq_desc_byt),
 153         X86_MATCH_VFM(INTEL_ATOM_SILVERMONT_MID,        &freq_desc_tng),
 154         X86_MATCH_VFM(INTEL_ATOM_AIRMONT,       &freq_desc_cht),
 155         X86_MATCH_VFM(INTEL_ATOM_AIRMONT_MID,   &freq_desc_ann),
 156         X86_MATCH_VFM(INTEL_ATOM_AIRMONT_NP,    &freq_desc_lgm),
 157         {}
 158 };
 159
 160 /*
 161  * MSR-based CPU/TSC frequency discovery for certain CPUs.
 162  *
 163  * Set global "lapic_timer_period" to bus_clock_cycles/jiffy
 164  * Return processor base frequency in KHz, or 0 on failure.
 165  */
 166 unsigned long cpu_khz_from_msr(void)
 167 {
 168         u32 lo, hi, ratio, freq, tscref;
 169         const struct freq_desc *freq_desc;
 170         const struct x86_cpu_id *id;
 171         const struct muldiv *md;
 172         unsigned long res;
 173         int index;
 174
 175         id = x86_match_cpu(tsc_msr_cpu_ids);
 176         if (!id)
 177                 return 0;
 178
 179         freq_desc = (struct freq_desc *)id->driver_data;
 180         if (freq_desc->use_msr_plat) {
 181                 rdmsr(MSR_PLATFORM_INFO, lo, hi);
 182                 ratio = (lo >> 8) & 0xff;
 183         } else {
 184                 rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
 185                 ratio = (hi >> 8) & 0x1f;
 186         }
 187
 188         /* Get FSB FREQ ID */
 189         rdmsr(MSR_FSB_FREQ, lo, hi);
 190         index = lo & freq_desc->mask;
 191         md = &freq_desc->muldiv[index];
 192
 193         /*
 194          * Note this also catches cases where the index points to an unpopulated
 195          * part of muldiv, in that case the else will set freq and res to 0.
 196          */
 197         if (md->divider) {
 198                 tscref = TSC_REFERENCE_KHZ * md->multiplier;
 199                 freq = DIV_ROUND_CLOSEST(tscref, md->divider);
 200                 /*
 201                  * Multiplying by ratio before the division has better
 202                  * accuracy than just calculating freq * ratio.
 203                  */
 204                 res = DIV_ROUND_CLOSEST(tscref * ratio, md->divider);
 205         } else {
 206                 freq = freq_desc->freqs[index];
 207                 res = freq * ratio;
 208         }
 209
 210         if (freq == 0)
 211                 pr_err("Error MSR_FSB_FREQ index %d is unknown\n", index);
 212
 213 #ifdef CONFIG_X86_LOCAL_APIC
 214         lapic_timer_period = (freq * 1000) / HZ;
 215 #endif
 216
 217         /*
 218          * TSC frequency determined by MSR is always considered "known"
 219          * because it is reported by HW.
 220          * Another fact is that on MSR capable platforms, PIT/HPET is
 221          * generally not available so calibration won't work at all.
 222          */
 223         setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
 224
 225         /*
 226          * Unfortunately there is no way for hardware to tell whether the
 227          * TSC is reliable.  We were told by silicon design team that TSC
 228          * on Atom SoCs are always "reliable". TSC is also the only
 229          * reliable clocksource on these SoCs (HPET is either not present
 230          * or not functional) so mark TSC reliable which removes the
 231          * requirement for a watchdog clocksource.
 232          */
 233         setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
 234
 235         return res;
 236 }