/*
 *  (c) 2005-2015 Advanced Micro Devices, Inc.
 *  Your use of this code is subject to the terms and conditions of the
 *  GNU general public license version 2. See "COPYING" or
 *  http://www.gnu.org/licenses/gpl.html
 *
 *  Written by Jacob Shin - AMD, Inc.
 *  Maintained by: Borislav Petkov <bp@alien8.de>
 *
 *  All MC4_MISCi registers are shared between cores on a node.
 */
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/kobject.h>
#include <linux/percpu.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/sysfs.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/cpu.h>
#include <linux/smp.h>

#include <asm/amd_nb.h>
#include <asm/apic.h>
#include <asm/idle.h>
#include <asm/mce.h>
#include <asm/msr.h>
#include <asm/trace/irq_vectors.h>

#define NR_BLOCKS         9
#define THRESHOLD_MAX     0xFFF
#define INT_TYPE_APIC     0x00020000
#define MASK_VALID_HI     0x80000000
#define MASK_CNTP_HI      0x40000000
#define MASK_LOCKED_HI    0x20000000
#define MASK_LVTOFF_HI    0x00F00000
#define MASK_COUNT_EN_HI  0x00080000
#define MASK_INT_TYPE_HI  0x00060000
#define MASK_OVERFLOW_HI  0x00010000
#define MASK_ERR_COUNT_HI 0x00000FFF
#define MASK_BLKPTR_LO    0xFF000000
#define MCG_XBLK_ADDR     0xC0000400

/* Deferred error settings */
#define MSR_CU_DEF_ERR          0xC0000410
#define MASK_DEF_LVTOFF         0x000000F0
#define MASK_DEF_INT_TYPE       0x00000006
#define DEF_LVT_OFF             0x2
#define DEF_INT_TYPE_APIC       0x2

static const char * const th_names[] = {
        "load_store",
        "insn_fetch",
        "combined_unit",
        "",
        "northbridge",
        "execution_unit",
};

static DEFINE_PER_CPU(struct threshold_bank **, threshold_banks);
static DEFINE_PER_CPU(unsigned char, bank_map); /* see which banks are on */

static void amd_threshold_interrupt(void);
static void amd_deferred_error_interrupt(void);

static void default_deferred_error_interrupt(void)
{
        pr_err("Unexpected deferred interrupt at vector %x\n", DEFERRED_ERROR_VECTOR);
}
void (*deferred_error_int_vector)(void) = default_deferred_error_interrupt;

/*
 * CPU Initialization
 */

struct thresh_restart {
        struct threshold_block  *b;
        int                     reset;
        int                     set_lvt_off;
        int                     lvt_off;
        u16                     old_limit;
};

static inline bool is_shared_bank(int bank)
{
        /* Bank 4 is for northbridge reporting and is thus shared */
        return (bank == 4);
}

static const char *bank4_names(const struct threshold_block *b)
{
        switch (b->address) {
        /* MSR4_MISC0 */
        case 0x00000413:
                return "dram";

        case 0xc0000408:
                return "ht_links";

        case 0xc0000409:
                return "l3_cache";

        default:
                WARN(1, "Funny MSR: 0x%08x\n", b->address);
                return "";
        }
};


static bool lvt_interrupt_supported(unsigned int bank, u32 msr_high_bits)
{
        /*
         * bank 4 supports APIC LVT interrupts implicitly since forever.
         */
        if (bank == 4)
                return true;

        /*
         * IntP: interrupt present; if this bit is set, the thresholding
         * bank can generate APIC LVT interrupts
         */
        return msr_high_bits & BIT(28);
}

static int lvt_off_valid(struct threshold_block *b, int apic, u32 lo, u32 hi)
{
        int msr = (hi & MASK_LVTOFF_HI) >> 20;

        if (apic < 0) {
                pr_err(FW_BUG "cpu %d, failed to setup threshold interrupt "
                       "for bank %d, block %d (MSR%08X=0x%x%08x)\n", b->cpu,
                       b->bank, b->block, b->address, hi, lo);
                return 0;
        }

        if (apic != msr) {
                pr_err(FW_BUG "cpu %d, invalid threshold interrupt offset %d "
                       "for bank %d, block %d (MSR%08X=0x%x%08x)\n",
                       b->cpu, apic, b->bank, b->block, b->address, hi, lo);
                return 0;
        }

        return 1;
};

/*
 * Called via smp_call_function_single(), must be called with correct
 * cpu affinity.
 */
static void threshold_restart_bank(void *_tr)
{
        struct thresh_restart *tr = _tr;
        u32 hi, lo;

        rdmsr(tr->b->address, lo, hi);

        if (tr->b->threshold_limit < (hi & THRESHOLD_MAX))
                tr->reset = 1;  /* limit cannot be lower than err count */

        if (tr->reset) {                /* reset err count and overflow bit */
                hi =
                    (hi & ~(MASK_ERR_COUNT_HI | MASK_OVERFLOW_HI)) |
                    (THRESHOLD_MAX - tr->b->threshold_limit);
        } else if (tr->old_limit) {     /* change limit w/o reset */
                int new_count = (hi & THRESHOLD_MAX) +
                    (tr->old_limit - tr->b->threshold_limit);

                hi = (hi & ~MASK_ERR_COUNT_HI) |
                    (new_count & THRESHOLD_MAX);
        }

        /* clear IntType */
        hi &= ~MASK_INT_TYPE_HI;

        if (!tr->b->interrupt_capable)
                goto done;

        if (tr->set_lvt_off) {
                if (lvt_off_valid(tr->b, tr->lvt_off, lo, hi)) {
                        /* set new lvt offset */
                        hi &= ~MASK_LVTOFF_HI;
                        hi |= tr->lvt_off << 20;
                }
        }

        if (tr->b->interrupt_enable)
                hi |= INT_TYPE_APIC;

 done:

        hi |= MASK_COUNT_EN_HI;
        wrmsr(tr->b->address, lo, hi);
}

static void mce_threshold_block_init(struct threshold_block *b, int offset)
{
        struct thresh_restart tr = {
                .b                      = b,
                .set_lvt_off            = 1,
                .lvt_off                = offset,
        };

        b->threshold_limit              = THRESHOLD_MAX;
        threshold_restart_bank(&tr);
};

static int setup_APIC_mce_threshold(int reserved, int new)
{
        if (reserved < 0 && !setup_APIC_eilvt(new, THRESHOLD_APIC_VECTOR,
                                              APIC_EILVT_MSG_FIX, 0))
                return new;

        return reserved;
}

static int setup_APIC_deferred_error(int reserved, int new)
{
        if (reserved < 0 && !setup_APIC_eilvt(new, DEFERRED_ERROR_VECTOR,
                                              APIC_EILVT_MSG_FIX, 0))
                return new;

        return reserved;
}

static void deferred_error_interrupt_enable(struct cpuinfo_x86 *c)
{
        u32 low = 0, high = 0;
        int def_offset = -1, def_new;

        if (rdmsr_safe(MSR_CU_DEF_ERR, &low, &high))
                return;

        def_new = (low & MASK_DEF_LVTOFF) >> 4;
        if (!(low & MASK_DEF_LVTOFF)) {
                pr_err(FW_BUG "Your BIOS is not setting up LVT offset 0x2 for deferred error IRQs correctly.\n");
                def_new = DEF_LVT_OFF;
                low = (low & ~MASK_DEF_LVTOFF) | (DEF_LVT_OFF << 4);
        }

        def_offset = setup_APIC_deferred_error(def_offset, def_new);
        if ((def_offset == def_new) &&
            (deferred_error_int_vector != amd_deferred_error_interrupt))
                deferred_error_int_vector = amd_deferred_error_interrupt;

        low = (low & ~MASK_DEF_INT_TYPE) | DEF_INT_TYPE_APIC;
        wrmsr(MSR_CU_DEF_ERR, low, high);
}

/* cpu init entry point, called from mce.c with preempt off */
void mce_amd_feature_init(struct cpuinfo_x86 *c)
{
        struct threshold_block b;
        unsigned int cpu = smp_processor_id();
        u32 low = 0, high = 0, address = 0;
        unsigned int bank, block;
        int offset = -1, new;

        for (bank = 0; bank < mca_cfg.banks; ++bank) {
                for (block = 0; block < NR_BLOCKS; ++block) {
                        if (block == 0)
                                address = MSR_IA32_MCx_MISC(bank);
                        else if (block == 1) {
                                address = (low & MASK_BLKPTR_LO) >> 21;
                                if (!address)
                                        break;

                                address += MCG_XBLK_ADDR;
                        } else
                                ++address;

                        if (rdmsr_safe(address, &low, &high))
                                break;

                        if (!(high & MASK_VALID_HI))
                                continue;

                        if (!(high & MASK_CNTP_HI)  ||
                             (high & MASK_LOCKED_HI))
                                continue;

                        if (!block)
                                per_cpu(bank_map, cpu) |= (1 << bank);

                        memset(&b, 0, sizeof(b));
                        b.cpu                   = cpu;
                        b.bank                  = bank;
                        b.block                 = block;
                        b.address               = address;
                        b.interrupt_capable     = lvt_interrupt_supported(bank, high);

                        if (!b.interrupt_capable)
                                goto init;

                        b.interrupt_enable = 1;
                        new     = (high & MASK_LVTOFF_HI) >> 20;
                        offset  = setup_APIC_mce_threshold(offset, new);

                        if ((offset == new) &&
                            (mce_threshold_vector != amd_threshold_interrupt))
                                mce_threshold_vector = amd_threshold_interrupt;

init:
                        mce_threshold_block_init(&b, offset);
                }
        }

        if (mce_flags.succor)
                deferred_error_interrupt_enable(c);
}

static void __log_error(unsigned int bank, bool threshold_err, u64 misc)
{
        struct mce m;
        u64 status;

        rdmsrl(MSR_IA32_MCx_STATUS(bank), status);
        if (!(status & MCI_STATUS_VAL))
                return;

        mce_setup(&m);

        m.status = status;
        m.bank = bank;

        if (threshold_err)
                m.misc = misc;

        if (m.status & MCI_STATUS_ADDRV)
                rdmsrl(MSR_IA32_MCx_ADDR(bank), m.addr);

        mce_log(&m);
        wrmsrl(MSR_IA32_MCx_STATUS(bank), 0);
}

static inline void __smp_deferred_error_interrupt(void)
{
        inc_irq_stat(irq_deferred_error_count);
        deferred_error_int_vector();
}

asmlinkage __visible void smp_deferred_error_interrupt(void)
{
        entering_irq();
        __smp_deferred_error_interrupt();
        exiting_ack_irq();
}

asmlinkage __visible void smp_trace_deferred_error_interrupt(void)
{
        entering_irq();
        trace_deferred_error_apic_entry(DEFERRED_ERROR_VECTOR);
        __smp_deferred_error_interrupt();
        trace_deferred_error_apic_exit(DEFERRED_ERROR_VECTOR);
        exiting_ack_irq();
}

/* APIC interrupt handler for deferred errors */
static void amd_deferred_error_interrupt(void)
{
        u64 status;
        unsigned int bank;

        for (bank = 0; bank < mca_cfg.banks; ++bank) {
                rdmsrl(MSR_IA32_MCx_STATUS(bank), status);

                if (!(status & MCI_STATUS_VAL) ||
                    !(status & MCI_STATUS_DEFERRED))
                        continue;

                __log_error(bank, false, 0);
                break;
        }
}

/*
 * APIC Interrupt Handler
 */

/*
 * threshold interrupt handler will service THRESHOLD_APIC_VECTOR.
 * the interrupt goes off when error_count reaches threshold_limit.
 * the handler will simply log mcelog w/ software defined bank number.
 */

static void amd_threshold_interrupt(void)
{
        u32 low = 0, high = 0, address = 0;
        int cpu = smp_processor_id();
        unsigned int bank, block;

        /* assume first bank caused it */
        for (bank = 0; bank < mca_cfg.banks; ++bank) {
                if (!(per_cpu(bank_map, cpu) & (1 << bank)))
                        continue;
                for (block = 0; block < NR_BLOCKS; ++block) {
                        if (block == 0) {
                                address = MSR_IA32_MCx_MISC(bank);
                        } else if (block == 1) {
                                address = (low & MASK_BLKPTR_LO) >> 21;
                                if (!address)
                                        break;
                                address += MCG_XBLK_ADDR;
                        } else {
                                ++address;
                        }

                        if (rdmsr_safe(address, &low, &high))
                                break;

                        if (!(high & MASK_VALID_HI)) {
                                if (block)
                                        continue;
                                else
                                        break;
                        }

                        if (!(high & MASK_CNTP_HI)  ||
                             (high & MASK_LOCKED_HI))
                                continue;

                        /*
                         * Log the machine check that caused the threshold
                         * event.
                         */
                        if (high & MASK_OVERFLOW_HI)
                                goto log;
                }
        }
        return;

log:
        __log_error(bank, true, ((u64)high << 32) | low);
}

/*
 * Sysfs Interface
 */

struct threshold_attr {
        struct attribute attr;
        ssize_t (*show) (struct threshold_block *, char *);
        ssize_t (*store) (struct threshold_block *, const char *, size_t count);
};

#define SHOW_FIELDS(name)                                               \
static ssize_t show_ ## name(struct threshold_block *b, char *buf)      \
{                                                                       \
        return sprintf(buf, "%lu\n", (unsigned long) b->name);          \
}
SHOW_FIELDS(interrupt_enable)
SHOW_FIELDS(threshold_limit)

static ssize_t
store_interrupt_enable(struct threshold_block *b, const char *buf, size_t size)
{
        struct thresh_restart tr;
        unsigned long new;

        if (!b->interrupt_capable)
                return -EINVAL;

        if (kstrtoul(buf, 0, &new) < 0)
                return -EINVAL;

        b->interrupt_enable = !!new;

        memset(&tr, 0, sizeof(tr));
        tr.b            = b;

        smp_call_function_single(b->cpu, threshold_restart_bank, &tr, 1);

        return size;
}

static ssize_t
store_threshold_limit(struct threshold_block *b, const char *buf, size_t size)
{
        struct thresh_restart tr;
        unsigned long new;

        if (kstrtoul(buf, 0, &new) < 0)
                return -EINVAL;

        if (new > THRESHOLD_MAX)
                new = THRESHOLD_MAX;
        if (new < 1)
                new = 1;

        memset(&tr, 0, sizeof(tr));
        tr.old_limit = b->threshold_limit;
        b->threshold_limit = new;
        tr.b = b;

        smp_call_function_single(b->cpu, threshold_restart_bank, &tr, 1);

        return size;
}

static ssize_t show_error_count(struct threshold_block *b, char *buf)
{
        u32 lo, hi;

        rdmsr_on_cpu(b->cpu, b->address, &lo, &hi);

        return sprintf(buf, "%u\n", ((hi & THRESHOLD_MAX) -
                                     (THRESHOLD_MAX - b->threshold_limit)));
}

static struct threshold_attr error_count = {
        .attr = {.name = __stringify(error_count), .mode = 0444 },
        .show = show_error_count,
};

#define RW_ATTR(val)                                                    \
static struct threshold_attr val = {                                    \
        .attr   = {.name = __stringify(val), .mode = 0644 },            \
        .show   = show_## val,                                          \
        .store  = store_## val,                                         \
};

RW_ATTR(interrupt_enable);
RW_ATTR(threshold_limit);

static struct attribute *default_attrs[] = {
        &threshold_limit.attr,
        &error_count.attr,
        NULL,   /* possibly interrupt_enable if supported, see below */
        NULL,
};

#define to_block(k)     container_of(k, struct threshold_block, kobj)
#define to_attr(a)      container_of(a, struct threshold_attr, attr)

static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf)
{
        struct threshold_block *b = to_block(kobj);
        struct threshold_attr *a = to_attr(attr);
        ssize_t ret;

        ret = a->show ? a->show(b, buf) : -EIO;

        return ret;
}

static ssize_t store(struct kobject *kobj, struct attribute *attr,
                     const char *buf, size_t count)
{
        struct threshold_block *b = to_block(kobj);
        struct threshold_attr *a = to_attr(attr);
        ssize_t ret;

        ret = a->store ? a->store(b, buf, count) : -EIO;

        return ret;
}

static const struct sysfs_ops threshold_ops = {
        .show                   = show,
        .store                  = store,
};

static struct kobj_type threshold_ktype = {
        .sysfs_ops              = &threshold_ops,
        .default_attrs          = default_attrs,
};

static int allocate_threshold_blocks(unsigned int cpu, unsigned int bank,
                                     unsigned int block, u32 address)
{
        struct threshold_block *b = NULL;
        u32 low, high;
        int err;

        if ((bank >= mca_cfg.banks) || (block >= NR_BLOCKS))
                return 0;

        if (rdmsr_safe_on_cpu(cpu, address, &low, &high))
                return 0;

        if (!(high & MASK_VALID_HI)) {
                if (block)
                        goto recurse;
                else
                        return 0;
        }

        if (!(high & MASK_CNTP_HI)  ||
             (high & MASK_LOCKED_HI))
                goto recurse;

        b = kzalloc(sizeof(struct threshold_block), GFP_KERNEL);
        if (!b)
                return -ENOMEM;

        b->block                = block;
        b->bank                 = bank;
        b->cpu                  = cpu;
        b->address              = address;
        b->interrupt_enable     = 0;
        b->interrupt_capable    = lvt_interrupt_supported(bank, high);
        b->threshold_limit      = THRESHOLD_MAX;

        if (b->interrupt_capable) {
                threshold_ktype.default_attrs[2] = &interrupt_enable.attr;
                b->interrupt_enable = 1;
        } else {
                threshold_ktype.default_attrs[2] = NULL;
        }

        INIT_LIST_HEAD(&b->miscj);

        if (per_cpu(threshold_banks, cpu)[bank]->blocks) {
                list_add(&b->miscj,
                         &per_cpu(threshold_banks, cpu)[bank]->blocks->miscj);
        } else {
                per_cpu(threshold_banks, cpu)[bank]->blocks = b;
        }

        err = kobject_init_and_add(&b->kobj, &threshold_ktype,
                                   per_cpu(threshold_banks, cpu)[bank]->kobj,
                                   (bank == 4 ? bank4_names(b) : th_names[bank]));
        if (err)
                goto out_free;
recurse:
        if (!block) {
                address = (low & MASK_BLKPTR_LO) >> 21;
                if (!address)
                        return 0;
                address += MCG_XBLK_ADDR;
        } else {
                ++address;
        }

        err = allocate_threshold_blocks(cpu, bank, ++block, address);
        if (err)
                goto out_free;

        if (b)
                kobject_uevent(&b->kobj, KOBJ_ADD);

        return err;

out_free:
        if (b) {
                kobject_put(&b->kobj);
                list_del(&b->miscj);
                kfree(b);
        }
        return err;
}

static int __threshold_add_blocks(struct threshold_bank *b)
{
        struct list_head *head = &b->blocks->miscj;
        struct threshold_block *pos = NULL;
        struct threshold_block *tmp = NULL;
        int err = 0;

        err = kobject_add(&b->blocks->kobj, b->kobj, b->blocks->kobj.name);
        if (err)
                return err;

        list_for_each_entry_safe(pos, tmp, head, miscj) {

                err = kobject_add(&pos->kobj, b->kobj, pos->kobj.name);
                if (err) {
                        list_for_each_entry_safe_reverse(pos, tmp, head, miscj)
                                kobject_del(&pos->kobj);

                        return err;
                }
        }
        return err;
}

static int threshold_create_bank(unsigned int cpu, unsigned int bank)
{
        struct device *dev = per_cpu(mce_device, cpu);
        struct amd_northbridge *nb = NULL;
        struct threshold_bank *b = NULL;
        const char *name = th_names[bank];
        int err = 0;

        if (is_shared_bank(bank)) {
                nb = node_to_amd_nb(amd_get_nb_id(cpu));

                /* threshold descriptor already initialized on this node? */
                if (nb && nb->bank4) {
                        /* yes, use it */
                        b = nb->bank4;
                        err = kobject_add(b->kobj, &dev->kobj, name);
                        if (err)
                                goto out;

                        per_cpu(threshold_banks, cpu)[bank] = b;
                        atomic_inc(&b->cpus);

                        err = __threshold_add_blocks(b);

                        goto out;
                }
        }

        b = kzalloc(sizeof(struct threshold_bank), GFP_KERNEL);
        if (!b) {
                err = -ENOMEM;
                goto out;
        }

        b->kobj = kobject_create_and_add(name, &dev->kobj);
        if (!b->kobj) {
                err = -EINVAL;
                goto out_free;
        }

        per_cpu(threshold_banks, cpu)[bank] = b;

        if (is_shared_bank(bank)) {
                atomic_set(&b->cpus, 1);

                /* nb is already initialized, see above */
                if (nb) {
                        WARN_ON(nb->bank4);
                        nb->bank4 = b;
                }
        }

        err = allocate_threshold_blocks(cpu, bank, 0, MSR_IA32_MCx_MISC(bank));
        if (!err)
                goto out;

 out_free:
        kfree(b);

 out:
        return err;
}

/* create dir/files for all valid threshold banks */
static int threshold_create_device(unsigned int cpu)
{
        unsigned int bank;
        struct threshold_bank **bp;
        int err = 0;

        bp = kzalloc(sizeof(struct threshold_bank *) * mca_cfg.banks,
                     GFP_KERNEL);
        if (!bp)
                return -ENOMEM;

        per_cpu(threshold_banks, cpu) = bp;

        for (bank = 0; bank < mca_cfg.banks; ++bank) {
                if (!(per_cpu(bank_map, cpu) & (1 << bank)))
                        continue;
                err = threshold_create_bank(cpu, bank);
                if (err)
                        return err;
        }

        return err;
}

static void deallocate_threshold_block(unsigned int cpu,
                                                 unsigned int bank)
{
        struct threshold_block *pos = NULL;
        struct threshold_block *tmp = NULL;
        struct threshold_bank *head = per_cpu(threshold_banks, cpu)[bank];

        if (!head)
                return;

        list_for_each_entry_safe(pos, tmp, &head->blocks->miscj, miscj) {
                kobject_put(&pos->kobj);
                list_del(&pos->miscj);
                kfree(pos);
        }

        kfree(per_cpu(threshold_banks, cpu)[bank]->blocks);
        per_cpu(threshold_banks, cpu)[bank]->blocks = NULL;
}

static void __threshold_remove_blocks(struct threshold_bank *b)
{
        struct threshold_block *pos = NULL;
        struct threshold_block *tmp = NULL;

        kobject_del(b->kobj);

        list_for_each_entry_safe(pos, tmp, &b->blocks->miscj, miscj)
                kobject_del(&pos->kobj);
}

static void threshold_remove_bank(unsigned int cpu, int bank)
{
        struct amd_northbridge *nb;
        struct threshold_bank *b;

        b = per_cpu(threshold_banks, cpu)[bank];
        if (!b)
                return;

        if (!b->blocks)
                goto free_out;

        if (is_shared_bank(bank)) {
                if (!atomic_dec_and_test(&b->cpus)) {
                        __threshold_remove_blocks(b);
                        per_cpu(threshold_banks, cpu)[bank] = NULL;
                        return;
                } else {
                        /*
                         * the last CPU on this node using the shared bank is
                         * going away, remove that bank now.
                         */
                        nb = node_to_amd_nb(amd_get_nb_id(cpu));
                        nb->bank4 = NULL;
                }
        }

        deallocate_threshold_block(cpu, bank);

free_out:
        kobject_del(b->kobj);
        kobject_put(b->kobj);
        kfree(b);
        per_cpu(threshold_banks, cpu)[bank] = NULL;
}

static void threshold_remove_device(unsigned int cpu)
{
        unsigned int bank;

        for (bank = 0; bank < mca_cfg.banks; ++bank) {
                if (!(per_cpu(bank_map, cpu) & (1 << bank)))
                        continue;
                threshold_remove_bank(cpu, bank);
        }
        kfree(per_cpu(threshold_banks, cpu));
}

/* get notified when a cpu comes on/off */
static void
amd_64_threshold_cpu_callback(unsigned long action, unsigned int cpu)
{
        switch (action) {
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
                threshold_create_device(cpu);
                break;
        case CPU_DEAD:
        case CPU_DEAD_FROZEN:
                threshold_remove_device(cpu);
                break;
        default:
                break;
        }
}

static __init int threshold_init_device(void)
{
        unsigned lcpu = 0;

        /* to hit CPUs online before the notifier is up */
        for_each_online_cpu(lcpu) {
                int err = threshold_create_device(lcpu);

                if (err)
                        return err;
        }
        threshold_cpu_callback = amd_64_threshold_cpu_callback;

        return 0;
}
/*
 * there are 3 funcs which need to be _initcalled in a logic sequence:
 * 1. xen_late_init_mcelog
 * 2. mcheck_init_device
 * 3. threshold_init_device
 *
 * xen_late_init_mcelog must register xen_mce_chrdev_device before
 * native mce_chrdev_device registration if running under xen platform;
 *
 * mcheck_init_device should be inited before threshold_init_device to
 * initialize mce_device, otherwise a NULL ptr dereference will cause panic.
 *
 * so we use following _initcalls
 * 1. device_initcall(xen_late_init_mcelog);
 * 2. device_initcall_sync(mcheck_init_device);
 * 3. late_initcall(threshold_init_device);
 *
 * when running under xen, the initcall order is 1,2,3;
 * on baremetal, we skip 1 and we do only 2 and 3.
 */
late_initcall(threshold_init_device);