x86, pat/mtrr: Rendezvous all the cpus for MTRR/PAT init

[linux-2.6/mini2440.git] / arch / x86 / kernel / cpu / mtrr / main.c

/*  Generic MTRR (Memory Type Range Register) driver.

    Copyright (C) 1997-2000  Richard Gooch
    Copyright (c) 2002       Patrick Mochel

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public
    License along with this library; if not, write to the Free
    Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

    Richard Gooch may be reached by email at  rgooch@atnf.csiro.au
    The postal address is:
      Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia.

    Source: "Pentium Pro Family Developer's Manual, Volume 3:
    Operating System Writer's Guide" (Intel document number 242692),
    section 11.11.7

    This was cleaned and made readable by Patrick Mochel <mochel@osdl.org>
    on 6-7 March 2002.
    Source: Intel Architecture Software Developers Manual, Volume 3:
    System Programming Guide; Section 9.11. (1997 edition - PPro).
*/

#define DEBUG

#include <linux/types.h> /* FIXME: kvm_para.h needs this */

#include <linux/kvm_para.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/init.h>
#include <linux/sort.h>
#include <linux/cpu.h>
#include <linux/pci.h>
#include <linux/smp.h>

#include <asm/processor.h>
#include <asm/e820.h>
#include <asm/mtrr.h>
#include <asm/msr.h>

#include "mtrr.h"

u32 num_var_ranges;

unsigned int mtrr_usage_table[MTRR_MAX_VAR_RANGES];
static DEFINE_MUTEX(mtrr_mutex);

u64 size_or_mask, size_and_mask;
u32 mtrr_aps_delayed_init;

static struct mtrr_ops *mtrr_ops[X86_VENDOR_NUM];

struct mtrr_ops *mtrr_if;

static void set_mtrr(unsigned int reg, unsigned long base,
                     unsigned long size, mtrr_type type);

void set_mtrr_ops(struct mtrr_ops *ops)
{
        if (ops->vendor && ops->vendor < X86_VENDOR_NUM)
                mtrr_ops[ops->vendor] = ops;
}

/*  Returns non-zero if we have the write-combining memory type  */
static int have_wrcomb(void)
{
        struct pci_dev *dev;
        u8 rev;

        dev = pci_get_class(PCI_CLASS_BRIDGE_HOST << 8, NULL);
        if (dev != NULL) {
                /*
                 * ServerWorks LE chipsets < rev 6 have problems with
                 * write-combining. Don't allow it and leave room for other
                 * chipsets to be tagged
                 */
                if (dev->vendor == PCI_VENDOR_ID_SERVERWORKS &&
                    dev->device == PCI_DEVICE_ID_SERVERWORKS_LE) {
                        pci_read_config_byte(dev, PCI_CLASS_REVISION, &rev);
                        if (rev <= 5) {
                                pr_info("mtrr: Serverworks LE rev < 6 detected. Write-combining disabled.\n");
                                pci_dev_put(dev);
                                return 0;
                        }
                }
                /*
                 * Intel 450NX errata # 23. Non ascending cacheline evictions to
                 * write combining memory may resulting in data corruption
                 */
                if (dev->vendor == PCI_VENDOR_ID_INTEL &&
                    dev->device == PCI_DEVICE_ID_INTEL_82451NX) {
                        pr_info("mtrr: Intel 450NX MMC detected. Write-combining disabled.\n");
                        pci_dev_put(dev);
                        return 0;
                }
                pci_dev_put(dev);
        }
        return mtrr_if->have_wrcomb ? mtrr_if->have_wrcomb() : 0;
}

/*  This function returns the number of variable MTRRs  */
static void __init set_num_var_ranges(void)
{
        unsigned long config = 0, dummy;

        if (use_intel())
                rdmsr(MSR_MTRRcap, config, dummy);
        else if (is_cpu(AMD))
                config = 2;
        else if (is_cpu(CYRIX) || is_cpu(CENTAUR))
                config = 8;

        num_var_ranges = config & 0xff;
}

static void __init init_table(void)
{
        int i, max;

        max = num_var_ranges;
        for (i = 0; i < max; i++)
                mtrr_usage_table[i] = 1;
}

struct set_mtrr_data {
        atomic_t        count;
        atomic_t        gate;
        unsigned long   smp_base;
        unsigned long   smp_size;
        unsigned int    smp_reg;
        mtrr_type       smp_type;
};

/**
 * ipi_handler - Synchronisation handler. Executed by "other" CPUs.
 *
 * Returns nothing.
 */
static void ipi_handler(void *info)
{
#ifdef CONFIG_SMP
        struct set_mtrr_data *data = info;
        unsigned long flags;

        local_irq_save(flags);

        atomic_dec(&data->count);
        while (!atomic_read(&data->gate))
                cpu_relax();

        /*  The master has cleared me to execute  */
        if (data->smp_reg != ~0U) {
                mtrr_if->set(data->smp_reg, data->smp_base,
                             data->smp_size, data->smp_type);
        } else if (mtrr_aps_delayed_init) {
                /*
                 * Initialize the MTRRs inaddition to the synchronisation.
                 */
                mtrr_if->set_all();
        }

        atomic_dec(&data->count);
        while (atomic_read(&data->gate))
                cpu_relax();

        atomic_dec(&data->count);
        local_irq_restore(flags);
#endif
}

static inline int types_compatible(mtrr_type type1, mtrr_type type2)
{
        return type1 == MTRR_TYPE_UNCACHABLE ||
               type2 == MTRR_TYPE_UNCACHABLE ||
               (type1 == MTRR_TYPE_WRTHROUGH && type2 == MTRR_TYPE_WRBACK) ||
               (type1 == MTRR_TYPE_WRBACK && type2 == MTRR_TYPE_WRTHROUGH);
}

/**
 * set_mtrr - update mtrrs on all processors
 * @reg:        mtrr in question
 * @base:       mtrr base
 * @size:       mtrr size
 * @type:       mtrr type
 *
 * This is kinda tricky, but fortunately, Intel spelled it out for us cleanly:
 *
 * 1. Send IPI to do the following:
 * 2. Disable Interrupts
 * 3. Wait for all procs to do so
 * 4. Enter no-fill cache mode
 * 5. Flush caches
 * 6. Clear PGE bit
 * 7. Flush all TLBs
 * 8. Disable all range registers
 * 9. Update the MTRRs
 * 10. Enable all range registers
 * 11. Flush all TLBs and caches again
 * 12. Enter normal cache mode and reenable caching
 * 13. Set PGE
 * 14. Wait for buddies to catch up
 * 15. Enable interrupts.
 *
 * What does that mean for us? Well, first we set data.count to the number
 * of CPUs. As each CPU disables interrupts, it'll decrement it once. We wait
 * until it hits 0 and proceed. We set the data.gate flag and reset data.count.
 * Meanwhile, they are waiting for that flag to be set. Once it's set, each
 * CPU goes through the transition of updating MTRRs.
 * The CPU vendors may each do it differently,
 * so we call mtrr_if->set() callback and let them take care of it.
 * When they're done, they again decrement data->count and wait for data.gate
 * to be reset.
 * When we finish, we wait for data.count to hit 0 and toggle the data.gate flag
 * Everyone then enables interrupts and we all continue on.
 *
 * Note that the mechanism is the same for UP systems, too; all the SMP stuff
 * becomes nops.
 */
static void
set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type type)
{
        struct set_mtrr_data data;
        unsigned long flags;

        data.smp_reg = reg;
        data.smp_base = base;
        data.smp_size = size;
        data.smp_type = type;
        atomic_set(&data.count, num_booting_cpus() - 1);

        /* Make sure data.count is visible before unleashing other CPUs */
        smp_wmb();
        atomic_set(&data.gate, 0);

        /* Start the ball rolling on other CPUs */
        if (smp_call_function(ipi_handler, &data, 0) != 0)
                panic("mtrr: timed out waiting for other CPUs\n");

        local_irq_save(flags);

        while (atomic_read(&data.count))
                cpu_relax();

        /* Ok, reset count and toggle gate */
        atomic_set(&data.count, num_booting_cpus() - 1);
        smp_wmb();
        atomic_set(&data.gate, 1);

        /* Do our MTRR business */

        /*
         * HACK!
         * We use this same function to initialize the mtrrs on boot.
         * The state of the boot cpu's mtrrs has been saved, and we want
         * to replicate across all the APs.
         * If we're doing that @reg is set to something special...
         */
        if (reg != ~0U)
                mtrr_if->set(reg, base, size, type);
        else if (!mtrr_aps_delayed_init)
                mtrr_if->set_all();

        /* Wait for the others */
        while (atomic_read(&data.count))
                cpu_relax();

        atomic_set(&data.count, num_booting_cpus() - 1);
        smp_wmb();
        atomic_set(&data.gate, 0);

        /*
         * Wait here for everyone to have seen the gate change
         * So we're the last ones to touch 'data'
         */
        while (atomic_read(&data.count))
                cpu_relax();

        local_irq_restore(flags);
}

/**
 * mtrr_add_page - Add a memory type region
 * @base: Physical base address of region in pages (in units of 4 kB!)
 * @size: Physical size of region in pages (4 kB)
 * @type: Type of MTRR desired
 * @increment: If this is true do usage counting on the region
 *
 * Memory type region registers control the caching on newer Intel and
 * non Intel processors. This function allows drivers to request an
 * MTRR is added. The details and hardware specifics of each processor's
 * implementation are hidden from the caller, but nevertheless the
 * caller should expect to need to provide a power of two size on an
 * equivalent power of two boundary.
 *
 * If the region cannot be added either because all regions are in use
 * or the CPU cannot support it a negative value is returned. On success
 * the register number for this entry is returned, but should be treated
 * as a cookie only.
 *
 * On a multiprocessor machine the changes are made to all processors.
 * This is required on x86 by the Intel processors.
 *
 * The available types are
 *
 * %MTRR_TYPE_UNCACHABLE - No caching
 *
 * %MTRR_TYPE_WRBACK - Write data back in bursts whenever
 *
 * %MTRR_TYPE_WRCOMB - Write data back soon but allow bursts
 *
 * %MTRR_TYPE_WRTHROUGH - Cache reads but not writes
 *
 * BUGS: Needs a quiet flag for the cases where drivers do not mind
 * failures and do not wish system log messages to be sent.
 */
int mtrr_add_page(unsigned long base, unsigned long size,
                  unsigned int type, bool increment)
{
        unsigned long lbase, lsize;
        int i, replace, error;
        mtrr_type ltype;

        if (!mtrr_if)
                return -ENXIO;

        error = mtrr_if->validate_add_page(base, size, type);
        if (error)
                return error;

        if (type >= MTRR_NUM_TYPES) {
                pr_warning("mtrr: type: %u invalid\n", type);
                return -EINVAL;
        }

        /* If the type is WC, check that this processor supports it */
        if ((type == MTRR_TYPE_WRCOMB) && !have_wrcomb()) {
                pr_warning("mtrr: your processor doesn't support write-combining\n");
                return -ENOSYS;
        }

        if (!size) {
                pr_warning("mtrr: zero sized request\n");
                return -EINVAL;
        }

        if (base & size_or_mask || size & size_or_mask) {
                pr_warning("mtrr: base or size exceeds the MTRR width\n");
                return -EINVAL;
        }

        error = -EINVAL;
        replace = -1;

        /* No CPU hotplug when we change MTRR entries */
        get_online_cpus();

        /* Search for existing MTRR  */
        mutex_lock(&mtrr_mutex);
        for (i = 0; i < num_var_ranges; ++i) {
                mtrr_if->get(i, &lbase, &lsize, &ltype);
                if (!lsize || base > lbase + lsize - 1 ||
                    base + size - 1 < lbase)
                        continue;
                /*
                 * At this point we know there is some kind of
                 * overlap/enclosure
                 */
                if (base < lbase || base + size - 1 > lbase + lsize - 1) {
                        if (base <= lbase &&
                            base + size - 1 >= lbase + lsize - 1) {
                                /*  New region encloses an existing region  */
                                if (type == ltype) {
                                        replace = replace == -1 ? i : -2;
                                        continue;
                                } else if (types_compatible(type, ltype))
                                        continue;
                        }
                        pr_warning("mtrr: 0x%lx000,0x%lx000 overlaps existing"
                                " 0x%lx000,0x%lx000\n", base, size, lbase,
                                lsize);
                        goto out;
                }
                /* New region is enclosed by an existing region */
                if (ltype != type) {
                        if (types_compatible(type, ltype))
                                continue;
                        pr_warning("mtrr: type mismatch for %lx000,%lx000 old: %s new: %s\n",
                                base, size, mtrr_attrib_to_str(ltype),
                                mtrr_attrib_to_str(type));
                        goto out;
                }
                if (increment)
                        ++mtrr_usage_table[i];
                error = i;
                goto out;
        }
        /* Search for an empty MTRR */
        i = mtrr_if->get_free_region(base, size, replace);
        if (i >= 0) {
                set_mtrr(i, base, size, type);
                if (likely(replace < 0)) {
                        mtrr_usage_table[i] = 1;
                } else {
                        mtrr_usage_table[i] = mtrr_usage_table[replace];
                        if (increment)
                                mtrr_usage_table[i]++;
                        if (unlikely(replace != i)) {
                                set_mtrr(replace, 0, 0, 0);
                                mtrr_usage_table[replace] = 0;
                        }
                }
        } else {
                pr_info("mtrr: no more MTRRs available\n");
        }
        error = i;
 out:
        mutex_unlock(&mtrr_mutex);
        put_online_cpus();
        return error;
}

static int mtrr_check(unsigned long base, unsigned long size)
{
        if ((base & (PAGE_SIZE - 1)) || (size & (PAGE_SIZE - 1))) {
                pr_warning("mtrr: size and base must be multiples of 4 kiB\n");
                pr_debug("mtrr: size: 0x%lx  base: 0x%lx\n", size, base);
                dump_stack();
                return -1;
        }
        return 0;
}

/**
 * mtrr_add - Add a memory type region
 * @base: Physical base address of region
 * @size: Physical size of region
 * @type: Type of MTRR desired
 * @increment: If this is true do usage counting on the region
 *
 * Memory type region registers control the caching on newer Intel and
 * non Intel processors. This function allows drivers to request an
 * MTRR is added. The details and hardware specifics of each processor's
 * implementation are hidden from the caller, but nevertheless the
 * caller should expect to need to provide a power of two size on an
 * equivalent power of two boundary.
 *
 * If the region cannot be added either because all regions are in use
 * or the CPU cannot support it a negative value is returned. On success
 * the register number for this entry is returned, but should be treated
 * as a cookie only.
 *
 * On a multiprocessor machine the changes are made to all processors.
 * This is required on x86 by the Intel processors.
 *
 * The available types are
 *
 * %MTRR_TYPE_UNCACHABLE - No caching
 *
 * %MTRR_TYPE_WRBACK - Write data back in bursts whenever
 *
 * %MTRR_TYPE_WRCOMB - Write data back soon but allow bursts
 *
 * %MTRR_TYPE_WRTHROUGH - Cache reads but not writes
 *
 * BUGS: Needs a quiet flag for the cases where drivers do not mind
 * failures and do not wish system log messages to be sent.
 */
int mtrr_add(unsigned long base, unsigned long size, unsigned int type,
             bool increment)
{
        if (mtrr_check(base, size))
                return -EINVAL;
        return mtrr_add_page(base >> PAGE_SHIFT, size >> PAGE_SHIFT, type,
                             increment);
}
EXPORT_SYMBOL(mtrr_add);

/**
 * mtrr_del_page - delete a memory type region
 * @reg: Register returned by mtrr_add
 * @base: Physical base address
 * @size: Size of region
 *
 * If register is supplied then base and size are ignored. This is
 * how drivers should call it.
 *
 * Releases an MTRR region. If the usage count drops to zero the
 * register is freed and the region returns to default state.
 * On success the register is returned, on failure a negative error
 * code.
 */
int mtrr_del_page(int reg, unsigned long base, unsigned long size)
{
        int i, max;
        mtrr_type ltype;
        unsigned long lbase, lsize;
        int error = -EINVAL;

        if (!mtrr_if)
                return -ENXIO;

        max = num_var_ranges;
        /* No CPU hotplug when we change MTRR entries */
        get_online_cpus();
        mutex_lock(&mtrr_mutex);
        if (reg < 0) {
                /*  Search for existing MTRR  */
                for (i = 0; i < max; ++i) {
                        mtrr_if->get(i, &lbase, &lsize, &ltype);
                        if (lbase == base && lsize == size) {
                                reg = i;
                                break;
                        }
                }
                if (reg < 0) {
                        pr_debug("mtrr: no MTRR for %lx000,%lx000 found\n",
                                 base, size);
                        goto out;
                }
        }
        if (reg >= max) {
                pr_warning("mtrr: register: %d too big\n", reg);
                goto out;
        }
        mtrr_if->get(reg, &lbase, &lsize, &ltype);
        if (lsize < 1) {
                pr_warning("mtrr: MTRR %d not used\n", reg);
                goto out;
        }
        if (mtrr_usage_table[reg] < 1) {
                pr_warning("mtrr: reg: %d has count=0\n", reg);
                goto out;
        }
        if (--mtrr_usage_table[reg] < 1)
                set_mtrr(reg, 0, 0, 0);
        error = reg;
 out:
        mutex_unlock(&mtrr_mutex);
        put_online_cpus();
        return error;
}

/**
 * mtrr_del - delete a memory type region
 * @reg: Register returned by mtrr_add
 * @base: Physical base address
 * @size: Size of region
 *
 * If register is supplied then base and size are ignored. This is
 * how drivers should call it.
 *
 * Releases an MTRR region. If the usage count drops to zero the
 * register is freed and the region returns to default state.
 * On success the register is returned, on failure a negative error
 * code.
 */
int mtrr_del(int reg, unsigned long base, unsigned long size)
{
        if (mtrr_check(base, size))
                return -EINVAL;
        return mtrr_del_page(reg, base >> PAGE_SHIFT, size >> PAGE_SHIFT);
}
EXPORT_SYMBOL(mtrr_del);

/*
 * HACK ALERT!
 * These should be called implicitly, but we can't yet until all the initcall
 * stuff is done...
 */
static void __init init_ifs(void)
{
#ifndef CONFIG_X86_64
        amd_init_mtrr();
        cyrix_init_mtrr();
        centaur_init_mtrr();
#endif
}

/* The suspend/resume methods are only for CPU without MTRR. CPU using generic
 * MTRR driver doesn't require this
 */
struct mtrr_value {
        mtrr_type       ltype;
        unsigned long   lbase;
        unsigned long   lsize;
};

static struct mtrr_value mtrr_value[MTRR_MAX_VAR_RANGES];

static int mtrr_save(struct sys_device *sysdev, pm_message_t state)
{
        int i;

        for (i = 0; i < num_var_ranges; i++) {
                mtrr_if->get(i, &mtrr_value[i].lbase,
                                &mtrr_value[i].lsize,
                                &mtrr_value[i].ltype);
        }
        return 0;
}

static int mtrr_restore(struct sys_device *sysdev)
{
        int i;

        for (i = 0; i < num_var_ranges; i++) {
                if (mtrr_value[i].lsize) {
                        set_mtrr(i, mtrr_value[i].lbase,
                                    mtrr_value[i].lsize,
                                    mtrr_value[i].ltype);
                }
        }
        return 0;
}



static struct sysdev_driver mtrr_sysdev_driver = {
        .suspend        = mtrr_save,
        .resume         = mtrr_restore,
};

int __initdata changed_by_mtrr_cleanup;

/**
 * mtrr_bp_init - initialize mtrrs on the boot CPU
 *
 * This needs to be called early; before any of the other CPUs are
 * initialized (i.e. before smp_init()).
 *
 */
void __init mtrr_bp_init(void)
{
        u32 phys_addr;

        init_ifs();

        phys_addr = 32;

        if (cpu_has_mtrr) {
                mtrr_if = &generic_mtrr_ops;
                size_or_mask = 0xff000000;                      /* 36 bits */
                size_and_mask = 0x00f00000;
                phys_addr = 36;

                /*
                 * This is an AMD specific MSR, but we assume(hope?) that
                 * Intel will implement it to when they extend the address
                 * bus of the Xeon.
                 */
                if (cpuid_eax(0x80000000) >= 0x80000008) {
                        phys_addr = cpuid_eax(0x80000008) & 0xff;
                        /* CPUID workaround for Intel 0F33/0F34 CPU */
                        if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
                            boot_cpu_data.x86 == 0xF &&
                            boot_cpu_data.x86_model == 0x3 &&
                            (boot_cpu_data.x86_mask == 0x3 ||
                             boot_cpu_data.x86_mask == 0x4))
                                phys_addr = 36;

                        size_or_mask = ~((1ULL << (phys_addr - PAGE_SHIFT)) - 1);
                        size_and_mask = ~size_or_mask & 0xfffff00000ULL;
                } else if (boot_cpu_data.x86_vendor == X86_VENDOR_CENTAUR &&
                           boot_cpu_data.x86 == 6) {
                        /*
                         * VIA C* family have Intel style MTRRs,
                         * but don't support PAE
                         */
                        size_or_mask = 0xfff00000;              /* 32 bits */
                        size_and_mask = 0;
                        phys_addr = 32;
                }
        } else {
                switch (boot_cpu_data.x86_vendor) {
                case X86_VENDOR_AMD:
                        if (cpu_has_k6_mtrr) {
                                /* Pre-Athlon (K6) AMD CPU MTRRs */
                                mtrr_if = mtrr_ops[X86_VENDOR_AMD];
                                size_or_mask = 0xfff00000;      /* 32 bits */
                                size_and_mask = 0;
                        }
                        break;
                case X86_VENDOR_CENTAUR:
                        if (cpu_has_centaur_mcr) {
                                mtrr_if = mtrr_ops[X86_VENDOR_CENTAUR];
                                size_or_mask = 0xfff00000;      /* 32 bits */
                                size_and_mask = 0;
                        }
                        break;
                case X86_VENDOR_CYRIX:
                        if (cpu_has_cyrix_arr) {
                                mtrr_if = mtrr_ops[X86_VENDOR_CYRIX];
                                size_or_mask = 0xfff00000;      /* 32 bits */
                                size_and_mask = 0;
                        }
                        break;
                default:
                        break;
                }
        }

        if (mtrr_if) {
                set_num_var_ranges();
                init_table();
                if (use_intel()) {
                        get_mtrr_state();

                        if (mtrr_cleanup(phys_addr)) {
                                changed_by_mtrr_cleanup = 1;
                                mtrr_if->set_all();
                        }
                }
        }
}

void mtrr_ap_init(void)
{
        if (!use_intel() || mtrr_aps_delayed_init)
                return;
        /*
         * Ideally we should hold mtrr_mutex here to avoid mtrr entries
         * changed, but this routine will be called in cpu boot time,
         * holding the lock breaks it.
         *
         * This routine is called in two cases:
         *
         *   1. very earily time of software resume, when there absolutely
         *      isn't mtrr entry changes;
         *
         *   2. cpu hotadd time. We let mtrr_add/del_page hold cpuhotplug
         *      lock to prevent mtrr entry changes
         */
        set_mtrr(~0U, 0, 0, 0);
}

/**
 * Save current fixed-range MTRR state of the BSP
 */
void mtrr_save_state(void)
{
        smp_call_function_single(0, mtrr_save_fixed_ranges, NULL, 1);
}

void set_mtrr_aps_delayed_init(void)
{
        if (!use_intel())
                return;

        mtrr_aps_delayed_init = 1;
}

/*
 * MTRR initialization for all AP's
 */
void mtrr_aps_init(void)
{
        if (!use_intel())
                return;

        set_mtrr(~0U, 0, 0, 0);
        mtrr_aps_delayed_init = 0;
}

void mtrr_bp_restore(void)
{
        if (!use_intel())
                return;

        mtrr_if->set_all();
}

static int __init mtrr_init_finialize(void)
{
        if (!mtrr_if)
                return 0;

        if (use_intel()) {
                if (!changed_by_mtrr_cleanup)
                        mtrr_state_warn();
                return 0;
        }

        /*
         * The CPU has no MTRR and seems to not support SMP. They have
         * specific drivers, we use a tricky method to support
         * suspend/resume for them.
         *
         * TBD: is there any system with such CPU which supports
         * suspend/resume? If no, we should remove the code.
         */
        sysdev_driver_register(&cpu_sysdev_class, &mtrr_sysdev_driver);

        return 0;
}
subsys_initcall(mtrr_init_finialize);