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Diffstat (limited to 'arch/x86/kernel/tsc_msr.c')
| -rw-r--r-- | arch/x86/kernel/tsc_msr.c | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc_msr.c b/arch/x86/kernel/tsc_msr.c new file mode 100644 index 000000000..92ae6acac --- /dev/null +++ b/arch/x86/kernel/tsc_msr.c @@ -0,0 +1,127 @@ +/* + * 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) & 0x1f; + } 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; +} |