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 /* 24 MHz crystal? : 24 * 13 / 4 = 78 MHz */ 138 static const struct freq_desc freq_desc_lgm = { 139 .use_msr_plat = true, 140 .freqs = { 78000, 78000, 78000, 78000, 78000, 78000, 78000, 78000 }, 141 .mask = 0x0f, 142 }; 143 144 static const struct x86_cpu_id tsc_msr_cpu_ids[] = { 145 X86_MATCH_INTEL_FAM6_MODEL(ATOM_SALTWELL_MID, &freq_desc_pnw), 146 X86_MATCH_INTEL_FAM6_MODEL(ATOM_SALTWELL_TABLET,&freq_desc_clv), 147 X86_MATCH_INTEL_FAM6_MODEL(ATOM_SILVERMONT, &freq_desc_byt), 148 X86_MATCH_INTEL_FAM6_MODEL(ATOM_SILVERMONT_MID, &freq_desc_tng), 149 X86_MATCH_INTEL_FAM6_MODEL(ATOM_AIRMONT, &freq_desc_cht), 150 X86_MATCH_INTEL_FAM6_MODEL(ATOM_AIRMONT_MID, &freq_desc_ann), 151 X86_MATCH_INTEL_FAM6_MODEL(ATOM_AIRMONT_NP, &freq_desc_lgm), 152 {} 153 }; 154 155 /* 156 * MSR-based CPU/TSC frequency discovery for certain CPUs. 157 * 158 * Set global "lapic_timer_period" to bus_clock_cycles/jiffy 159 * Return processor base frequency in KHz, or 0 on failure. 160 */ 161 unsigned long cpu_khz_from_msr(void) 162 { 163 u32 lo, hi, ratio, freq, tscref; 164 const struct freq_desc *freq_desc; 165 const struct x86_cpu_id *id; 166 const struct muldiv *md; 167 unsigned long res; 168 int index; 169 170 id = x86_match_cpu(tsc_msr_cpu_ids); 171 if (!id) 172 return 0; 173 174 freq_desc = (struct freq_desc *)id->driver_data; 175 if (freq_desc->use_msr_plat) { 176 rdmsr(MSR_PLATFORM_INFO, lo, hi); 177 ratio = (lo >> 8) & 0xff; 178 } else { 179 rdmsr(MSR_IA32_PERF_STATUS, lo, hi); 180 ratio = (hi >> 8) & 0x1f; 181 } 182 183 /* Get FSB FREQ ID */ 184 rdmsr(MSR_FSB_FREQ, lo, hi); 185 index = lo & freq_desc->mask; 186 md = &freq_desc->muldiv[index]; 187 188 /* 189 * Note this also catches cases where the index points to an unpopulated 190 * part of muldiv, in that case the else will set freq and res to 0. 191 */ 192 if (md->divider) { 193 tscref = TSC_REFERENCE_KHZ * md->multiplier; 194 freq = DIV_ROUND_CLOSEST(tscref, md->divider); 195 /* 196 * Multiplying by ratio before the division has better 197 * accuracy than just calculating freq * ratio. 198 */ 199 res = DIV_ROUND_CLOSEST(tscref * ratio, md->divider); 200 } else { 201 freq = freq_desc->freqs[index]; 202 res = freq * ratio; 203 } 204 205 if (freq == 0) 206 pr_err("Error MSR_FSB_FREQ index %d is unknown\n", index); 207 208 #ifdef CONFIG_X86_LOCAL_APIC 209 lapic_timer_period = (freq * 1000) / HZ; 210 #endif 211 212 /* 213 * TSC frequency determined by MSR is always considered "known" 214 * because it is reported by HW. 215 * Another fact is that on MSR capable platforms, PIT/HPET is 216 * generally not available so calibration won't work at all. 217 */ 218 setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ); 219 220 /* 221 * Unfortunately there is no way for hardware to tell whether the 222 * TSC is reliable. We were told by silicon design team that TSC 223 * on Atom SoCs are always "reliable". TSC is also the only 224 * reliable clocksource on these SoCs (HPET is either not present 225 * or not functional) so mark TSC reliable which removes the 226 * requirement for a watchdog clocksource. 227 */ 228 setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE); 229 230 return res; 231 } 232