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 38struct 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 */ 50struct 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 */ 66static 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 72static 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 */ 86static 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 */ 105static 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 */ 118static 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 */ 131static 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 */ 142static 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 149static 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 */ 166unsigned 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} 237