/*
* apb_timer.c: Driver for Langwell APB timers
*
* (C) Copyright 2009 Intel Corporation
* Author: Jacob Pan (jacob.jun.pan@intel.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; version 2
* of the License.
*
* Note:
* Langwell is the south complex of Intel Moorestown MID platform. There are
* eight external timers in total that can be used by the operating system.
* The timer information, such as frequency and addresses, is provided to the
* OS via SFI tables.
* Timer interrupts are routed via FW/HW emulated IOAPIC independently via
* individual redirection table entries (RTE).
* Unlike HPET, there is no master counter, therefore one of the timers are
* used as clocksource. The overall allocation looks like:
* - timer 0 - NR_CPUs for per cpu timer
* - one timer for clocksource
* - one timer for watchdog driver.
* It is also worth notice that APB timer does not support true one-shot mode,
* free-running mode will be used here to emulate one-shot mode.
* APB timer can also be used as broadcast timer along with per cpu local APIC
* timer, but by default APB timer has higher rating than local APIC timers.
*/
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/sysdev.h>
#include <linux/slab.h>
#include <linux/pm.h>
#include <linux/pci.h>
#include <linux/sfi.h>
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/irq.h>
#include <asm/fixmap.h>
#include <asm/apb_timer.h>
#include <asm/mrst.h>
#define APBT_MASK CLOCKSOURCE_MASK(32)
#define APBT_SHIFT 22
#define APBT_CLOCKEVENT_RATING 110
#define APBT_CLOCKSOURCE_RATING 250
#define APBT_MIN_DELTA_USEC 200
#define EVT_TO_APBT_DEV(evt) container_of(evt, struct apbt_dev, evt)
#define APBT_CLOCKEVENT0_NUM (0)
#define APBT_CLOCKEVENT1_NUM (1)
#define APBT_CLOCKSOURCE_NUM (2)
static unsigned long apbt_address;
static int apb_timer_block_enabled;
static void __iomem *apbt_virt_address;
static int phy_cs_timer_id;
/*
* Common DW APB timer info
*/
static uint64_t apbt_freq;
static void apbt_set_mode(enum clock_event_mode mode,
struct clock_event_device *evt);
static int apbt_next_event(unsigned long delta,
struct clock_event_device *evt);
static cycle_t apbt_read_clocksource(struct clocksource *cs);
static void apbt_restart_clocksource(struct clocksource *cs);
struct apbt_dev {
struct clock_event_device evt;
unsigned int num;
int cpu;
unsigned int irq;
unsigned int tick;
unsigned int count;
unsigned int flags;
char name[10];
};
static DEFINE_PER_CPU(struct apbt_dev, cpu_apbt_dev);
#ifdef CONFIG_SMP
static unsigned int apbt_num_timers_used;
static struct apbt_dev *apbt_devs;
#endif
static inline unsigned long apbt_readl_reg(unsigned long a)
{
return readl(apbt_virt_address + a);
}
static inline void apbt_writel_reg(unsigned long d, unsigned long a)
{
writel(d, apbt_virt_address + a);
}
static inline unsigned long apbt_readl(int n, unsigned long a)
{
return readl(apbt_virt_address + a + n * APBTMRS_REG_SIZE);
}
static inline void apbt_writel(int n, unsigned long d, unsigned long a)
{
writel(d, apbt_virt_address + a + n * APBTMRS_REG_SIZE);
}
static inline void apbt_set_mapping(void)
{
struct sfi_timer_table_entry *mtmr;
if (apbt_virt_address) {
pr_debug("APBT base already mapped\n");
return;
}
mtmr = sfi_get_mtmr(APBT_CLOCKEVENT0_NUM);
if (mtmr == NULL) {
printk(KERN_ERR "Failed to get MTMR %d from SFI\n",
APBT_CLOCKEVENT0_NUM);
return;
}
apbt_address = (unsigned long)mtmr->phys_addr;
if (!apbt_address) {
printk(KERN_WARNING "No timer base from SFI, use default\n");
apbt_address = APBT_DEFAULT_BASE;
}
apbt_virt_address = ioremap_nocache(apbt_address, APBT_MMAP_SIZE);
if (apbt_virt_address) {
pr_debug("Mapped APBT physical addr %p at virtual addr %p\n",\
(void *)apbt_address, (void *)apbt_virt_address);
} else {
pr_debug("Failed mapping APBT phy address at %p\n",\
(void *)apbt_address);
goto panic_noapbt;
}
apbt_freq = mtmr->freq_hz / USEC_PER_SEC;
sfi_free_mtmr(mtmr);
/* Now figure out the physical timer id for clocksource device */
mtmr = sfi_get_mtmr(APBT_CLOCKSOURCE_NUM);
if (mtmr == NULL)
goto panic_noapbt;
/* Now figure out the physical timer id */
phy_cs_timer_id = (unsigned int)(mtmr->phys_addr & 0xff)
/ APBTMRS_REG_SIZE;
pr_debug("Use timer %d for clocksource\n", phy_cs_timer_id);
return;
panic_noapbt:
panic("Failed to setup APB system timer\n");
}
static inline void apbt_clear_mapping(void)
{
iounmap(apbt_virt_address);
apbt_virt_address = NULL;
}
/*
* APBT timer interrupt enable / disable
*/
static inline int is_apbt_capable(void)
{
return apbt_virt_address ? 1 : 0;
}
static struct clocksource clocksource_apbt = {
.name = "apbt",
.rating = APBT_CLOCKSOURCE_RATING,
.read = apbt_read_clocksource,
.mask = APBT_MASK,
.shift = APBT_SHIFT,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
.resume = apbt_restart_clocksource,
};
/* boot APB clock event device */
static struct clock_event_device apbt_clockevent = {
.name = "apbt0",
.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
.set_mode = apbt_set_mode,
.set_next_event = apbt_next_event,
.shift = APBT_SHIFT,
.irq = 0,
.rating = APBT_CLOCKEVENT_RATING,
};
/*
* start count down from 0xffff_ffff. this is done by toggling the enable bit
* then load initial load count to ~0.
*/
static void apbt_start_counter(int n)
{
unsigned long ctrl = apbt_readl(n, APBTMR_N_CONTROL);
ctrl &= ~APBTMR_CONTROL_ENABLE;
apbt_writel(n, ctrl, APBTMR_N_CONTROL);
apbt_writel(n, ~0, APBTMR_N_LOAD_COUNT);
/* enable, mask interrupt */
ctrl &= ~APBTMR_CONTROL_MODE_PERIODIC;
ctrl |= (APBTMR_CONTROL_ENABLE | APBTMR_CONTROL_INT);
apbt_writel(n, ctrl, APBTMR_N_CONTROL);
/* read it once to get cached counter value initialized */
apbt_read_clocksource(&clocksource_apbt);
}
static irqreturn_t apbt_interrupt_handler(int irq, void *data)
{
struct apbt_dev *dev = (struct apbt_dev *)data;
struct clock_event_device *aevt = &dev->evt;
if (!aevt->event_handler) {
printk(KERN_INFO "Spurious APBT timer interrupt on %d\n",
dev->num);
return IRQ_NONE;
}
aevt->event_handler(aevt);
return IRQ_HANDLED;
}
static void apbt_restart_clocksource(struct clocksource *cs)
{
apbt_start_counter(phy_cs_timer_id);
}
static void apbt_enable_int(int n)
{
unsigned long ctrl = apbt_readl(n, APBTMR_N_CONTROL);
/* clear pending intr */
apbt_readl(n, APBTMR_N_EOI);
ctrl &= ~APBTMR_CONTROL_INT;
apbt_writel(n, ctrl, APBTMR_N_CONTROL);
}
static void apbt_disable_int(int n)
{
unsigned long ctrl = apbt_readl(n, APBTMR_N_CONTROL);
ctrl |= APBTMR_CONTROL_INT;
apbt_writel(n, ctrl, APBTMR_N_CONTROL);
}
static int __init apbt_clockevent_register(void)
{
struct sfi_timer_table_entry *mtmr;
struct apbt_dev *adev = &__get_cpu_var(cpu_apbt_dev);
mtmr = sfi_get_mtmr(APBT_CLOCKEVENT0_NUM);
if (mtmr == NULL) {
printk(KERN_ERR "Failed to get MTMR %d from SFI\n",
APBT_CLOCKEVENT0_NUM);
return -ENODEV;
}
/*
* We need to calculate the scaled math multiplication factor for
* nanosecond to apbt tick conversion.
* mult = (nsec/cycle)*2^APBT_SHIFT
*/
apbt_clockevent.mult = div_sc((unsigned long) mtmr->freq_hz
, NSEC_PER_SEC, APBT_SHIFT);
/* Calculate the min / max delta */
apbt_clockevent.max_delta_ns = clockevent_delta2ns(0x7FFFFFFF,
&apbt_clockevent);
apbt_clockevent.min_delta_ns = clockevent_delta2ns(
APBT_MIN_DELTA_USEC*apbt_freq,
&apbt_clockevent);
/*
* Start apbt with the boot cpu mask and make it
* global if not used for per cpu timer.
*/
apbt_clockevent.cpumask = cpumask_of(smp_processor_id());
adev->num = smp_processor_id();
memcpy(&adev->evt, &apbt_clockevent, sizeof(struct clock_event_device));
if (mrst_timer_options == MRST_TIMER_LAPIC_APBT) {
apbt_clockevent.rating = APBT_CLOCKEVENT_RATING - 100;
global_clock_event = &adev->evt;
printk(KERN_DEBUG "%s clockevent registered as global\n",
global_clock_event->name);
}
if (request_irq(apbt_clockevent.irq, apbt_interrupt_handler,
IRQF_TIMER | IRQF_DISABLED | IRQF_NOBALANCING,
apbt_clockevent.name, adev)) {
printk(KERN_ERR "Failed request IRQ for APBT%d\n",
apbt_clockevent.irq);
}
clockevents_register_device(&adev->evt);
/* Start APBT 0 interrupts */
apbt_enable_int(APBT_CLOCKEVENT0_NUM);
sfi_free_mtmr(mtmr);
return 0;
}
#ifdef CONFIG_SMP
static void apbt_setup_irq(struct apbt_dev *adev)
{
/* timer0 irq has been setup early */
if (adev->irq == 0)
return;
if (system_state == SYSTEM_BOOTING) {
irq_modify_status(adev->irq, 0, IRQ_MOVE_PCNTXT);
/* APB timer irqs are set up as mp_irqs, timer is edge type */
__set_irq_handler(adev->irq, handle_edge_irq, 0, "edge");
if (request_irq(adev->irq, apbt_interrupt_handler,
IRQF_TIMER | IRQF_DISABLED | IRQF_NOBALANCING,
adev->name, adev)) {
printk(KERN_ERR "Failed request IRQ for APBT%d\n",
adev->num);
}
} else
enable_irq(adev->irq);
}
/* Should be called with per cpu */
void apbt_setup_secondary_clock(void)
{
struct apbt_dev *adev;
struct clock_event_device *aevt;
int cpu;
/* Don't register boot CPU clockevent */
cpu = smp_processor_id();
if (!cpu)
return;
/*
* We need to calculate the scaled math multiplication factor for
* nanosecond to apbt tick conversion.
* mult = (nsec/cycle)*2^APBT_SHIFT
*/
printk(KERN_INFO "Init per CPU clockevent %d\n", cpu);
adev = &per_cpu(cpu_apbt_dev, cpu);
aevt = &adev->evt;
memcpy(aevt, &apbt_clockevent, sizeof(*aevt));
aevt->cpumask = cpumask_of(cpu);
aevt->name = adev->name;
aevt->mode = CLOCK_EVT_MODE_UNUSED;
printk(KERN_INFO "Registering CPU %d clockevent device %s, mask %08x\n",
cpu, aevt->name, *(u32 *)aevt->cpumask);
apbt_setup_irq(adev);
clockevents_register_device(aevt);
apbt_enable_int(cpu);
return;
}
/*
* this notify handler process CPU hotplug events. in case of S0i3, nonboot
* cpus are disabled/enabled frequently, for performance reasons, we keep the
* per cpu timer irq registered so that we do need to do free_irq/request_irq.
*
* TODO: it might be more reliable to directly disable percpu clockevent device
* without the notifier chain. currently, cpu 0 may get interrupts from other
* cpu timers during the offline process due to the ordering of notification.
* the extra interrupt is harmless.
*/
static int apbt_cpuhp_notify(struct notifier_block *n,
unsigned long action, void *hcpu)
{
unsigned long cpu = (unsigned long)hcpu;
struct apbt_dev *adev = &per_cpu(cpu_apbt_dev, cpu);
switch (action & 0xf) {
case CPU_DEAD:
disable_irq(adev->irq);
apbt_disable_int(cpu);
if (system_state == SYSTEM_RUNNING) {
pr_debug("skipping APBT CPU %lu offline\n", cpu);
} else if (adev) {
pr_debug("APBT clockevent for cpu %lu offline\n", cpu);
free_irq(adev->irq, adev);
}
break;
default:
pr_debug("APBT notified %lu, no action\n", action);
}
return NOTIFY_OK;
}
static __init int apbt_late_init(void)
{
if (mrst_timer_options == MRST_TIMER_LAPIC_APBT ||
!apb_timer_block_enabled)
return 0;
/* This notifier should be called after workqueue is ready */
hotcpu_notifier(apbt_cpuhp_notify, -20);
return 0;
}
fs_initcall(apbt_late_init);
#else
void apbt_setup_secondary_clock(void) {}
#endif /* CONFIG_SMP */
static void apbt_set_mode(enum clock_event_mode mode,
struct clock_event_device *evt)
{
unsigned long ctrl;
uint64_t delta;
int timer_num;
struct apbt_dev *adev = EVT_TO_APBT_DEV(evt);
BUG_ON(!apbt_virt_address);
timer_num = adev->num;
pr_debug("%s CPU %d timer %d mode=%d\n",
__func__, first_cpu(*evt->cpumask), timer_num, mode);
switch (mode) {
case CLOCK_EVT_MODE_PERIODIC:
delta = ((uint64_t)(NSEC_PER_SEC/HZ)) * apbt_clockevent.mult;
delta >>= apbt_clockevent.shift;
ctrl = apbt_readl(timer_num, APBTMR_N_CONTROL);
ctrl |= APBTMR_CONTROL_MODE_PERIODIC;
apbt_writel(timer_num, ctrl, APBTMR_N_CONTROL);
/*
* DW APB p. 46, have to disable timer before load counter,
* may cause sync problem.
*/
ctrl &= ~APBTMR_CONTROL_ENABLE;
apbt_writel(timer_num, ctrl, APBTMR_N_CONTROL);
udelay(1);
pr_debug("Setting clock period %d for HZ %d\n", (int)delta, HZ);
apbt_writel(timer_num, delta, APBTMR_N_LOAD_COUNT);
ctrl |= APBTMR_CONTROL_ENABLE;
apbt_writel(timer_num, ctrl, APBTMR_N_CONTROL);
break;
/* APB timer does not have one-shot mode, use free running mode */
case CLOCK_EVT_MODE_ONESHOT:
ctrl = apbt_readl(timer_num, APBTMR_N_CONTROL);
/*
* set free running mode, this mode will let timer reload max
* timeout which will give time (3min on 25MHz clock) to rearm
* the next event, therefore emulate the one-shot mode.
*/
ctrl &= ~APBTMR_CONTROL_ENABLE;
ctrl &= ~APBTMR_CONTROL_MODE_PERIODIC;
apbt_writel(timer_num, ctrl, APBTMR_N_CONTROL);
/* write again to set free running mode */
apbt_writel(timer_num, ctrl, APBTMR_N_CONTROL);
/*
* DW APB p. 46, load counter with all 1s before starting free
* running mode.
*/
apbt_writel(timer_num, ~0, APBTMR_N_LOAD_COUNT);
ctrl &= ~APBTMR_CONTROL_INT;
ctrl |= APBTMR_CONTROL_ENABLE;
apbt_writel(timer_num, ctrl, APBTMR_N_CONTROL);
break;
case CLOCK_EVT_MODE_UNUSED:
case CLOCK_EVT_MODE_SHUTDOWN:
apbt_disable_int(timer_num);
ctrl = apbt_readl(timer_num, APBTMR_N_CONTROL);
ctrl &= ~APBTMR_CONTROL_ENABLE;
apbt_writel(timer_num, ctrl, APBTMR_N_CONTROL);
break;
case CLOCK_EVT_MODE_RESUME:
apbt_enable_int(timer_num);
break;
}
}
static int apbt_next_event(unsigned long delta,
struct clock_event_device *evt)
{
unsigned long ctrl;
int timer_num;
struct apbt_dev *adev = EVT_TO_APBT_DEV(evt);
timer_num = adev->num;
/* Disable timer */
ctrl = apbt_readl(timer_num, APBTMR_N_CONTROL);
ctrl &= ~APBTMR_CONTROL_ENABLE;
apbt_writel(timer_num, ctrl, APBTMR_N_CONTROL);
/* write new count */
apbt_writel(timer_num, delta, APBTMR_N_LOAD_COUNT);
ctrl |= APBTMR_CONTROL_ENABLE;
apbt_writel(timer_num, ctrl, APBTMR_N_CONTROL);
return 0;
}
/*
* APB timer clock is not in sync with pclk on Langwell, which translates to
* unreliable read value caused by sampling error. the error does not add up
* overtime and only happens when sampling a 0 as a 1 by mistake. so the time
* would go backwards. the following code is trying to prevent time traveling
* backwards. little bit paranoid.
*/
static cycle_t apbt_read_clocksource(struct clocksource *cs)
{
unsigned long t0, t1, t2;
static unsigned long last_read;
bad_count:
t1 = apbt_readl(phy_cs_timer_id,
APBTMR_N_CURRENT_VALUE);
t2 = apbt_readl(phy_cs_timer_id,
APBTMR_N_CURRENT_VALUE);
if (unlikely(t1 < t2)) {
pr_debug("APBT: read current count error %lx:%lx:%lx\n",
t1, t2, t2 - t1);
goto bad_count;
}
/*
* check against cached last read, makes sure time does not go back.
* it could be a normal rollover but we will do tripple check anyway
*/
if (unlikely(t2 > last_read)) {
/* check if we have a normal rollover */
unsigned long raw_intr_status =
apbt_readl_reg(APBTMRS_RAW_INT_STATUS);
/*
* cs timer interrupt is masked but raw intr bit is set if
* rollover occurs. then we read EOI reg to clear it.
*/
if (raw_intr_status & (1 << phy_cs_timer_id)) {
apbt_readl(phy_cs_timer_id, APBTMR_N_EOI);
goto out;
}
pr_debug("APB CS going back %lx:%lx:%lx ",
t2, last_read, t2 - last_read);
bad_count_x3:
pr_debug("triple check enforced\n");
t0 = apbt_readl(phy_cs_timer_id,
APBTMR_N_CURRENT_VALUE);
udelay(1);
t1 = apbt_readl(phy_cs_timer_id,
APBTMR_N_CURRENT_VALUE);
udelay(1);
t2 = apbt_readl(phy_cs_timer_id,
APBTMR_N_CURRENT_VALUE);
if ((t2 > t1) || (t1 > t0)) {
printk(KERN_ERR "Error: APB CS tripple check failed\n");
goto bad_count_x3;
}
}
out:
last_read = t2;
return (cycle_t)~t2;
}
static int apbt_clocksource_register(void)
{
u64 start, now;
cycle_t t1;
/* Start the counter, use timer 2 as source, timer 0/1 for event */
apbt_start_counter(phy_cs_timer_id);
/* Verify whether apbt counter works */
t1 = apbt_read_clocksource(&clocksource_apbt);
rdtscll(start);
/*
* We don't know the TSC frequency yet, but waiting for
* 200000 TSC cycles is safe:
* 4 GHz == 50us
* 1 GHz == 200us
*/
do {
rep_nop();
rdtscll(now);
} while ((now - start) < 200000UL);
/* APBT is the only always on clocksource, it has to work! */
if (t1 == apbt_read_clocksource(&clocksource_apbt))
panic("APBT counter not counting. APBT disabled\n");
/*
* initialize and register APBT clocksource
* convert that to ns/clock cycle
* mult = (ns/c) * 2^APBT_SHIFT
*/
clocksource_apbt.mult = div_sc(MSEC_PER_SEC,
(unsigned long) apbt_freq, APBT_SHIFT);
clocksource_register(&clocksource_apbt);
return 0;
}
/*
* Early setup the APBT timer, only use timer 0 for booting then switch to
* per CPU timer if possible.
* returns 1 if per cpu apbt is setup
* returns 0 if no per cpu apbt is chosen
* panic if set up failed, this is the only platform timer on Moorestown.
*/
void __init apbt_time_init(void)
{
#ifdef CONFIG_SMP
int i;
struct sfi_timer_table_entry *p_mtmr;
unsigned int percpu_timer;
struct apbt_dev *adev;
#endif
if (apb_timer_block_enabled)
return;
apbt_set_mapping();
if (apbt_virt_address) {
pr_debug("Found APBT version 0x%lx\n",\
apbt_readl_reg(APBTMRS_COMP_VERSION));
} else
goto out_noapbt;
/*
* Read the frequency and check for a sane value, for ESL model
* we extend the possible clock range to allow time scaling.
*/
if (apbt_freq < APBT_MIN_FREQ || apbt_freq > APBT_MAX_FREQ) {
pr_debug("APBT has invalid freq 0x%llx\n", apbt_freq);
goto out_noapbt;
}
if (apbt_clocksource_register()) {
pr_debug("APBT has failed to register clocksource\n");
goto out_noapbt;
}
if (!apbt_clockevent_register())
apb_timer_block_enabled = 1;
else {
pr_debug("APBT has failed to register clockevent\n");
goto out_noapbt;
}
#ifdef CONFIG_SMP
/* kernel cmdline disable apb timer, so we will use lapic timers */
if (mrst_timer_options == MRST_TIMER_LAPIC_APBT) {
printk(KERN_INFO "apbt: disabled per cpu timer\n");
return;
}
pr_debug("%s: %d CPUs online\n", __func__, num_online_cpus());
if (num_possible_cpus() <= sfi_mtimer_num) {
percpu_timer = 1;
apbt_num_timers_used = num_possible_cpus();
} else {
percpu_timer = 0;
apbt_num_timers_used = 1;
adev = &per_cpu(cpu_apbt_dev, 0);
adev->flags &= ~APBT_DEV_USED;
}
pr_debug("%s: %d APB timers used\n", __func__, apbt_num_timers_used);
/* here we set up per CPU timer data structure */
apbt_devs = kzalloc(sizeof(struct apbt_dev) * apbt_num_timers_used,
GFP_KERNEL);
if (!apbt_devs) {
printk(KERN_ERR "Failed to allocate APB timer devices\n");
return;
}
for (i = 0; i < apbt_num_timers_used; i++) {
adev = &per_cpu(cpu_apbt_dev, i);
adev->num = i;
adev->cpu = i;
p_mtmr = sfi_get_mtmr(i);
if (p_mtmr) {
adev->tick = p_mtmr->freq_hz;
adev->irq = p_mtmr->irq;
} else
printk(KERN_ERR "Failed to get timer for cpu %d\n", i);
adev->count = 0;
sprintf(adev->name, "apbt%d", i);
}
#endif
return;
out_noapbt:
apbt_clear_mapping();
apb_timer_block_enabled = 0;
panic("failed to enable APB timer\n");
}
static inline void apbt_disable(int n)
{
if (is_apbt_capable()) {
unsigned long ctrl = apbt_readl(n, APBTMR_N_CONTROL);
ctrl &= ~APBTMR_CONTROL_ENABLE;
apbt_writel(n, ctrl, APBTMR_N_CONTROL);
}
}
/* called before apb_timer_enable, use early map */
unsigned long apbt_quick_calibrate()
{
int i, scale;
u64 old, new;
cycle_t t1, t2;
unsigned long khz = 0;
u32 loop, shift;
apbt_set_mapping();
apbt_start_counter(phy_cs_timer_id);
/* check if the timer can count down, otherwise return */
old = apbt_read_clocksource(&clocksource_apbt);
i = 10000;
while (--i) {
if (old != apbt_read_clocksource(&clocksource_apbt))
break;
}
if (!i)
goto failed;
/* count 16 ms */
loop = (apbt_freq * 1000) << 4;
/* restart the timer to ensure it won't get to 0 in the calibration */
apbt_start_counter(phy_cs_timer_id);
old = apbt_read_clocksource(&clocksource_apbt);
old += loop;
t1 = __native_read_tsc();
do {
new = apbt_read_clocksource(&clocksource_apbt);
} while (new < old);
t2 = __native_read_tsc();
shift = 5;
if (unlikely(loop >> shift == 0)) {
printk(KERN_INFO
"APBT TSC calibration failed, not enough resolution\n");
return 0;
}
scale = (int)div_u64((t2 - t1), loop >> shift);
khz = (scale * apbt_freq * 1000) >> shift;
printk(KERN_INFO "TSC freq calculated by APB timer is %lu khz\n", khz);
return khz;
failed:
return 0;
}
