linux/arch/x86/kernel/tsc_msr.c
Bin Gao f3a02ecebe x86/tsc: Set TSC_KNOWN_FREQ and TSC_RELIABLE flags on Intel Atom SoCs
TSC on Intel Atom SoCs capable of determining TSC frequency by MSR is
reliable and the frequency is known (provided by HW).

On these platforms PIT/HPET is generally not available so calibration won't
work at all and there is no other clocksource to act as a watchdog for the
TSC, so we have no other choice than to trust it.

Set both X86_FEATURE_TSC_KNOWN_FREQ and X86_FEATURE_TSC_RELIABLE flags to
make sure the calibration is skipped and no watchdog is required.

Signed-off-by: Bin Gao <bin.gao@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1479241644-234277-5-git-send-email-bin.gao@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-11-18 10:58:31 +01:00

124 lines
3.5 KiB
C

/*
* tsc_msr.c - TSC frequency enumeration via MSR
*
* 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>
#define MAX_NUM_FREQS 9
/*
* 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, 99840, 0, 83200 } },
/* CLV+ */
{ 6, 0x35, 0, { 0, 133200, 0, 0, 0, 99840, 0, 83200 } },
/* TNG - Intel Atom processor Z3400 series */
{ 6, 0x4a, 1, { 0, 100000, 133300, 0, 0, 0, 0, 0 } },
/* VLV2 - Intel Atom processor E3000, Z3600, Z3700 series */
{ 6, 0x37, 1, { 83300, 100000, 133300, 116700, 80000, 0, 0, 0 } },
/* ANN - Intel Atom processor Z3500 series */
{ 6, 0x5a, 1, { 83300, 100000, 133300, 100000, 0, 0, 0, 0 } },
/* AMT - Intel Atom processor X7-Z8000 and X5-Z8000 series */
{ 6, 0x4c, 1, { 83300, 100000, 133300, 116700,
80000, 93300, 90000, 88900, 87500 } },
};
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])
/*
* MSR-based CPU/TSC frequency discovery for certain CPUs.
*
* Set global "lapic_timer_frequency" to bus_clock_cycles/jiffy
* Return processor base frequency in KHz, or 0 on failure.
*/
unsigned long cpu_khz_from_msr(void)
{
u32 lo, hi, ratio, freq_id, freq;
unsigned long res;
int cpu_index;
if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
return 0;
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;
}
/* Get FSB FREQ ID */
rdmsr(MSR_FSB_FREQ, lo, hi);
freq_id = lo & 0x7;
freq = id_to_freq(cpu_index, freq_id);
/* TSC frequency = maximum resolved freq * maximum resolved bus ratio */
res = freq * ratio;
#ifdef CONFIG_X86_LOCAL_APIC
lapic_timer_frequency = (freq * 1000) / HZ;
#endif
/*
* TSC frequency determined by MSR is always considered "known"
* because it is reported by HW.
* Another fact is that on MSR capable platforms, PIT/HPET is
* generally not available so calibration won't work at all.
*/
setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
/*
* Unfortunately there is no way for hardware to tell whether the
* TSC is reliable. We were told by silicon design team that TSC
* on Atom SoCs are always "reliable". TSC is also the only
* reliable clocksource on these SoCs (HPET is either not present
* or not functional) so mark TSC reliable which removes the
* requirement for a watchdog clocksource.
*/
setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
return res;
}