[linux-2.6-block.git] / arch / x86 / kernel / apb_timer.c

/*
 * 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/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>

#define APBT_MASK      CLOCKSOURCE_MASK(32)
#define APBT_SHIFT                     22
#define APBT_CLOCKEVENT_RATING         150
#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(void);

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];
};

int disable_apbt_percpu __cpuinitdata;

#ifdef CONFIG_SMP
static unsigned int apbt_num_timers_used;
static DEFINE_PER_CPU(struct apbt_dev, cpu_apbt_dev);
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,
};

/*
 * if user does not want to use per CPU apb timer, just give it a lower rating
 * than local apic timer and skip the late per cpu timer init.
 */
static inline int __init setup_x86_mrst_timer(char *arg)
{
       if (!arg)
               return -EINVAL;

       if (strcmp("apbt_only", arg) == 0)
               disable_apbt_percpu = 0;
       else if (strcmp("lapic_and_apbt", arg) == 0)
               disable_apbt_percpu = 1;
       else {
               pr_warning("X86 MRST timer option %s not recognised"
                       " use x86_mrst_timer=apbt_only or lapic_and_apbt\n",
                       arg);
               return -EINVAL;
       }
       return 0;
}
__setup("x86_mrst_timer=", setup_x86_mrst_timer);

/*
 * 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(void)
{
       apbt_start_counter(phy_cs_timer_id);
}

/* Setup IRQ routing via IOAPIC */
#ifdef CONFIG_SMP
static void apbt_setup_irq(struct apbt_dev *adev)
{
       struct irq_chip *chip;
       struct irq_desc *desc;

       /* timer0 irq has been setup early */
       if (adev->irq == 0)
               return;
       desc = irq_to_desc(adev->irq);
       chip = get_irq_chip(adev->irq);
       disable_irq(adev->irq);
       desc->status |= IRQ_MOVE_PCNTXT;
       irq_set_affinity(adev->irq, cpumask_of(adev->cpu));
       /* APB timer irqs are set up as mp_irqs, timer is edge triggerred */
       set_irq_chip_and_handler_name(adev->irq, chip, handle_edge_irq, "edge");
       enable_irq(adev->irq);
       if (system_state == SYSTEM_BOOTING)
               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);
               }
}
#endif

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;

       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());

       if (disable_apbt_percpu) {
               apbt_clockevent.rating = APBT_CLOCKEVENT_RATING - 100;
               global_clock_event = &apbt_clockevent;
               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, &apbt_clockevent)) {
               printk(KERN_ERR "Failed request IRQ for APBT%d\n",
                       apbt_clockevent.irq);
       }

       clockevents_register_device(&apbt_clockevent);
       /* Start APBT 0 interrupts */
       apbt_enable_int(APBT_CLOCKEVENT0_NUM);

       sfi_free_mtmr(mtmr);
       return 0;
}

#ifdef CONFIG_SMP
/* 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 == boot_cpu_id)
               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:
               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(KERN_INFO "APBT notified %lu, no action\n", action);
       }
       return NOTIFY_OK;
}

static __init int apbt_late_init(void)
{
       if (disable_apbt_percpu)
               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);

       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(KERN_INFO "tripple 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 (disable_apbt_percpu) {
               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;
}