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/* * tsc_msr.c - MSR based TSC calibration on Intel Atom SoC platforms. * * TSC in Intel Atom SoC runs at a constant rate which can be figured * by this formula: * <maximum core-clock to bus-clock ratio> * <maximum resolved frequency> * See Intel 64 and IA-32 System Programming Guid section 16.12 and 30.11.5 * for details. * Especially some Intel Atom SoCs don't have PIT(i8254) or HPET, so MSR * based calibration is the only option. * * * Copyright (C) 2013 Intel Corporation * Author: Bin Gao <bin.gao@intel.com> * * This file is released under the GPLv2. */ #include <linux/kernel.h> #include <asm/processor.h> #include <asm/setup.h> #include <asm/apic.h> #include <asm/param.h> /* CPU reference clock frequency: in KHz */ #define FREQ_83 83200 #define FREQ_100 99840 #define FREQ_133 133200 #define FREQ_166 166400 #define MAX_NUM_FREQS 8 /* * According to Intel 64 and IA-32 System Programming Guide, * if MSR_PERF_STAT[31] is set, the maximum resolved bus ratio can be * read in MSR_PLATFORM_ID[12:8], otherwise in MSR_PERF_STAT[44:40]. * Unfortunately some Intel Atom SoCs aren't quite compliant to this, * so we need manually differentiate SoC families. This is what the * field msr_plat does. */ struct freq_desc { u8 x86_family; /* CPU family */ u8 x86_model; /* model */ u8 msr_plat; /* 1: use MSR_PLATFORM_INFO, 0: MSR_IA32_PERF_STATUS */ u32 freqs[MAX_NUM_FREQS]; }; static struct freq_desc freq_desc_tables[] = { /* PNW */ { 6, 0x27, 0, { 0, 0, 0, 0, 0, FREQ_100, 0, FREQ_83 } }, /* CLV+ */ { 6, 0x35, 0, { 0, FREQ_133, 0, 0, 0, FREQ_100, 0, FREQ_83 } }, /* TNG */ { 6, 0x4a, 1, { 0, FREQ_100, FREQ_133, 0, 0, 0, 0, 0 } }, /* VLV2 */ { 6, 0x37, 1, { FREQ_83, FREQ_100, FREQ_133, FREQ_166, 0, 0, 0, 0 } }, /* ANN */ { 6, 0x5a, 1, { FREQ_83, FREQ_100, FREQ_133, FREQ_100, 0, 0, 0, 0 } }, }; static int match_cpu(u8 family, u8 model) { int i; for (i = 0; i < ARRAY_SIZE(freq_desc_tables); i++) { if ((family == freq_desc_tables[i].x86_family) && (model == freq_desc_tables[i].x86_model)) return i; } return -1; } /* Map CPU reference clock freq ID(0-7) to CPU reference clock freq(KHz) */ #define id_to_freq(cpu_index, freq_id) \ (freq_desc_tables[cpu_index].freqs[freq_id]) /* * Do MSR calibration only for known/supported CPUs. * * Returns the calibration value or 0 if MSR calibration failed. */ unsigned long try_msr_calibrate_tsc(void) { u32 lo, hi, ratio, freq_id, freq; unsigned long res; int cpu_index; cpu_index = match_cpu(boot_cpu_data.x86, boot_cpu_data.x86_model); if (cpu_index < 0) return 0; if (freq_desc_tables[cpu_index].msr_plat) { rdmsr(MSR_PLATFORM_INFO, lo, hi); ratio = (lo >> 8) & 0xff; } else { rdmsr(MSR_IA32_PERF_STATUS, lo, hi); ratio = (hi >> 8) & 0x1f; } pr_info("Maximum core-clock to bus-clock ratio: 0x%x\n", ratio); if (!ratio) goto fail; /* Get FSB FREQ ID */ rdmsr(MSR_FSB_FREQ, lo, hi); freq_id = lo & 0x7; freq = id_to_freq(cpu_index, freq_id); pr_info("Resolved frequency ID: %u, frequency: %u KHz\n", freq_id, freq); if (!freq) goto fail; /* TSC frequency = maximum resolved freq * maximum resolved bus ratio */ res = freq * ratio; pr_info("TSC runs at %lu KHz\n", res); #ifdef CONFIG_X86_LOCAL_APIC lapic_timer_frequency = (freq * 1000) / HZ; pr_info("lapic_timer_frequency = %d\n", lapic_timer_frequency); #endif return res; fail: pr_warn("Fast TSC calibration using MSR failed\n"); return 0; }
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