kernel - Fix lockup due to recentn pmap change

[dragonfly.git] / sys / platform / pc64 / x86_64 / nexus.c

/*
 * Copyright 1998 Massachusetts Institute of Technology
 * Copyright (c) 2008 The DragonFly Project.
 *
 * Permission to use, copy, modify, and distribute this software and
 * its documentation for any purpose and without fee is hereby
 * granted, provided that both the above copyright notice and this
 * permission notice appear in all copies, that both the above
 * copyright notice and this permission notice appear in all
 * supporting documentation, and that the name of M.I.T. not be used
 * in advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.  M.I.T. makes
 * no representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied
 * warranty.
 * 
 * THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''.  M.I.T. DISCLAIMS
 * ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
 * SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD: src/sys/i386/i386/nexus.c,v 1.26.2.10 2003/02/22 13:16:45 imp Exp $
 */

/*
 * This code implements a `root nexus' for Intel Architecture
 * machines.  The function of the root nexus is to serve as an
 * attachment point for both processors and buses, and to manage
 * resources which are common to all of them.  In particular,
 * this code implements the core resource managers for interrupt
 * requests, DMA requests (which rightfully should be a part of the
 * ISA code but it's easier to do it here for now), I/O port addresses,
 * and I/O memory address space.
 */

#include "use_pci.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/bus.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/rman.h>
#include <sys/interrupt.h>
#include <sys/machintr.h>
#include <sys/linker.h>

#include <machine/vmparam.h>
#include <vm/vm.h>
#include <vm/pmap.h>
#include <machine/pmap.h>

#include <machine/nexusvar.h>
#include <machine/smp.h>
#include <machine/intr_machdep.h>
#include <machine_base/apic/lapic.h>
#include <machine_base/apic/ioapic.h>
#include <machine/pc/bios.h>
#include <machine/metadata.h>

#if NPCI > 0
#include "pcib_if.h"
#endif

#define I386_BUS_SPACE_IO       0       /* space is i/o space */
#define I386_BUS_SPACE_MEM      1       /* space is mem space */

#define ELF_KERN_STR    ("elf"__XSTRING(__ELF_WORD_SIZE)" kernel")

static MALLOC_DEFINE(M_NEXUSDEV, "nexusdev", "Nexus device");
struct nexus_device {
        struct resource_list    nx_resources;
        int                     nx_pcibus;
};

#define DEVTONX(dev)    ((struct nexus_device *)device_get_ivars(dev))

static struct rman irq_rman[MAXCPU], drq_rman, port_rman, mem_rman;

static  int nexus_probe(device_t);
static  int nexus_attach(device_t);
static  int nexus_print_all_resources(device_t dev);
static  int nexus_print_child(device_t, device_t);
static device_t nexus_add_child(device_t bus, device_t parent, int order,
                                const char *name, int unit);
static  struct resource *nexus_alloc_resource(device_t, device_t, int, int *,
    u_long, u_long, u_long, u_int, int);
static  int nexus_read_ivar(device_t, device_t, int, uintptr_t *);
static  int nexus_write_ivar(device_t, device_t, int, uintptr_t);
static  int nexus_activate_resource(device_t, device_t, int, int,
                                    struct resource *);
static  int nexus_deactivate_resource(device_t, device_t, int, int,
                                      struct resource *);
static  int nexus_release_resource(device_t, device_t, int, int,
                                   struct resource *);
static  int nexus_config_intr(device_t, device_t, int, enum intr_trigger,
                              enum intr_polarity);
static  int nexus_setup_intr(device_t, device_t, struct resource *, int flags,
                void (*)(void *), void *, void **, lwkt_serialize_t,
                const char *);
static  int nexus_teardown_intr(device_t, device_t, struct resource *,
                                void *);
static  int nexus_set_resource(device_t, device_t, int, int, u_long, u_long,
                               int);
static  int nexus_get_resource(device_t, device_t, int, int, u_long *, u_long *);
static void nexus_delete_resource(device_t, device_t, int, int);

#if NPCI > 0
static  int nexus_alloc_msi(device_t, device_t, int, int, int *, int);
static  int nexus_release_msi(device_t, device_t, int, int *, int);
static  int nexus_map_msi(device_t, device_t, int, uint64_t *, uint32_t *, int);
static  int nexus_alloc_msix(device_t, device_t, int *, int);
static  int nexus_release_msix(device_t, device_t, int, int);
#endif

/*
 * The device_identify method will cause nexus to automatically associate
 * and attach to the root bus.
 */
static device_method_t nexus_methods[] = {
        /* Device interface */
        DEVMETHOD(device_identify,      bus_generic_identify),
        DEVMETHOD(device_probe,         nexus_probe),
        DEVMETHOD(device_attach,        nexus_attach),
        DEVMETHOD(device_detach,        bus_generic_detach),
        DEVMETHOD(device_shutdown,      bus_generic_shutdown),
        DEVMETHOD(device_suspend,       bus_generic_suspend),
        DEVMETHOD(device_resume,        bus_generic_resume),

        /* Bus interface */
        DEVMETHOD(bus_print_child,      nexus_print_child),
        DEVMETHOD(bus_add_child,        nexus_add_child),
        DEVMETHOD(bus_read_ivar,        nexus_read_ivar),
        DEVMETHOD(bus_write_ivar,       nexus_write_ivar),
        DEVMETHOD(bus_alloc_resource,   nexus_alloc_resource),
        DEVMETHOD(bus_release_resource, nexus_release_resource),
        DEVMETHOD(bus_activate_resource, nexus_activate_resource),
        DEVMETHOD(bus_deactivate_resource, nexus_deactivate_resource),
        DEVMETHOD(bus_config_intr,      nexus_config_intr),
        DEVMETHOD(bus_setup_intr,       nexus_setup_intr),
        DEVMETHOD(bus_teardown_intr,    nexus_teardown_intr),
        DEVMETHOD(bus_set_resource,     nexus_set_resource),
        DEVMETHOD(bus_get_resource,     nexus_get_resource),
        DEVMETHOD(bus_delete_resource,  nexus_delete_resource),

#if NPCI > 0
        DEVMETHOD(pcib_alloc_msi,       nexus_alloc_msi),
        DEVMETHOD(pcib_release_msi,     nexus_release_msi),
        DEVMETHOD(pcib_map_msi,         nexus_map_msi),
        DEVMETHOD(pcib_alloc_msix,      nexus_alloc_msix),
        DEVMETHOD(pcib_release_msix,    nexus_release_msix),
#endif

        DEVMETHOD_END
};

static driver_t nexus_driver = {
        "nexus",
        nexus_methods,
        1,                      /* no softc */
};
static devclass_t nexus_devclass;

DRIVER_MODULE(nexus, root, nexus_driver, nexus_devclass, NULL, NULL);

static int
nexus_probe(device_t dev)
{
        int cpuid;

        device_quiet(dev);      /* suppress attach message for neatness */

        for (cpuid = 0; cpuid < ncpus; ++cpuid) {
                struct rman *rm = &irq_rman[cpuid];

                rm->rm_start = 0;
                rm->rm_end = IDT_HWI_VECTORS - 1;
                rm->rm_type = RMAN_ARRAY;
                rm->rm_descr = "Interrupt request lines";

                if (rman_init(rm, cpuid))
                        panic("%s rman_init", __func__);
                MachIntrABI.rman_setup(rm);
        }

        /*
         * ISA DMA on PCI systems is implemented in the ISA part of each
         * PCI->ISA bridge and the channels can be duplicated if there are
         * multiple bridges.  (eg: laptops with docking stations)
         */
        drq_rman.rm_start = 0;
        drq_rman.rm_end = 7;
        drq_rman.rm_type = RMAN_ARRAY;
        drq_rman.rm_descr = "DMA request lines";
        /* XXX drq 0 not available on some machines */
        if (rman_init(&drq_rman, -1)
            || rman_manage_region(&drq_rman,
                                  drq_rman.rm_start, drq_rman.rm_end))
                panic("%s drq_rman", __func__);

        /*
         * However, IO ports and Memory truely are global at this level,
         * as are APIC interrupts (however many IO APICS there turn out
         * to be on large systems..)
         */
        port_rman.rm_start = 0;
        port_rman.rm_end = 0xffff;
        port_rman.rm_type = RMAN_ARRAY;
        port_rman.rm_descr = "I/O ports";
        if (rman_init(&port_rman, -1)
            || rman_manage_region(&port_rman, 0, 0xffff))
                panic("%s port_rman", __func__);

        mem_rman.rm_start = 0;
        mem_rman.rm_end = ~0u;
        mem_rman.rm_type = RMAN_ARRAY;
        mem_rman.rm_descr = "I/O memory addresses";
        if (rman_init(&mem_rman, -1)
            || rman_manage_region(&mem_rman, 0, ~0))
                panic("%s mem_rman", __func__);

        return bus_generic_probe(dev);
}

static int
nexus_attach(device_t dev)
{
        device_t        child;

        /*
         * First, let our child driver's identify any child devices that
         * they can find.  Once that is done attach any devices that we
         * found.
         */
#if 0 /* FUTURE */
        bus_generic_probe(dev);
#endif
        bus_generic_attach(dev);

        /*
         * And if we didn't see ISA on a pci bridge, create a
         * connection point now so it shows up "on motherboard".
         */
        if (!devclass_get_device(devclass_find("isa"), 0)) {
                child = BUS_ADD_CHILD(dev, dev, 0, "isa", 0);
                if (child == NULL)
                        panic("%s isa", __func__);
                device_probe_and_attach(child);
        }

        return 0;
}

static int
nexus_print_all_resources(device_t dev)
{
        struct  nexus_device *ndev = DEVTONX(dev);
        struct resource_list *rl = &ndev->nx_resources;
        int retval = 0;

        if (SLIST_FIRST(rl) || ndev->nx_pcibus != -1)
                retval += kprintf(" at");

        retval += resource_list_print_type(rl, "port", SYS_RES_IOPORT, "%#lx");
        retval += resource_list_print_type(rl, "iomem", SYS_RES_MEMORY, "%#lx");
        retval += resource_list_print_type(rl, "irq", SYS_RES_IRQ, "%ld");

        return retval;
}

static int
nexus_print_child(device_t bus, device_t child)
{
        struct  nexus_device *ndev = DEVTONX(child);
        int retval = 0;

        retval += bus_print_child_header(bus, child);
        retval += nexus_print_all_resources(child);
        if (ndev->nx_pcibus != -1)
                retval += kprintf(" pcibus %d", ndev->nx_pcibus);
        retval += kprintf(" on motherboard\n");

        return (retval);
}

static device_t
nexus_add_child(device_t bus, device_t parent, int order,
                const char *name, int unit)
{
        device_t                child;
        struct nexus_device     *ndev;

        ndev = kmalloc(sizeof(struct nexus_device), M_NEXUSDEV, M_INTWAIT|M_ZERO);
        resource_list_init(&ndev->nx_resources);
        ndev->nx_pcibus = -1;

        child = device_add_child_ordered(parent, order, name, unit); 

        /* should we free this in nexus_child_detached? */
        device_set_ivars(child, ndev);

        return(child);
}

static int
nexus_read_ivar(device_t dev, device_t child, int which, uintptr_t *result)
{
        struct nexus_device *ndev = DEVTONX(child);

        switch (which) {
        case NEXUS_IVAR_PCIBUS:
                *result = ndev->nx_pcibus;
                break;
        default:
                return ENOENT;
        }
        return 0;
}

static int
nexus_write_ivar(device_t dev, device_t child, int which, uintptr_t value)
{
        struct nexus_device *ndev = DEVTONX(child);

        switch (which) {
        case NEXUS_IVAR_PCIBUS:
                ndev->nx_pcibus = value;
                break;
        default:
                return ENOENT;
        }
        return 0;
}

/*
 * Allocate a resource on behalf of child.  NB: child is usually going to be a
 * child of one of our descendants, not a direct child of nexus0.
 * (Exceptions include npx.)
 */
static struct resource *
nexus_alloc_resource(device_t bus, device_t child, int type, int *rid,
    u_long start, u_long end, u_long count, u_int flags, int cpuid)
{
        struct nexus_device *ndev = DEVTONX(child);
        struct  resource *rv;
        struct resource_list_entry *rle;
        struct  rman *rm;
        int needactivate = flags & RF_ACTIVE;

        /*
         * If this is an allocation of the "default" range for a given RID, and
         * we know what the resources for this device are (ie. they aren't maintained
         * by a child bus), then work out the start/end values.
         */
        if ((start == 0UL) && (end == ~0UL) && (count == 1)) {
                if (ndev == NULL)
                        return(NULL);
                rle = resource_list_find(&ndev->nx_resources, type, *rid);
                if (rle == NULL)
                        return(NULL);
                start = rle->start;
                end = rle->end;
                count = rle->count;
                cpuid = rle->cpuid;
        }

        flags &= ~RF_ACTIVE;

        switch (type) {
        case SYS_RES_IRQ:
                KASSERT(cpuid >= 0 && cpuid < ncpus,
                    ("nexus invalid cpuid: %d", cpuid));
                rm = &irq_rman[cpuid];
                break;

        case SYS_RES_DRQ:
                rm = &drq_rman;
                break;

        case SYS_RES_IOPORT:
                rm = &port_rman;
                break;

        case SYS_RES_MEMORY:
                rm = &mem_rman;
                break;

        default:
                return 0;
        }

        rv = rman_reserve_resource(rm, start, end, count, flags, child);
        if (rv == NULL)
                return 0;
        rman_set_rid(rv, *rid);

        if (type == SYS_RES_MEMORY) {
                rman_set_bustag(rv, I386_BUS_SPACE_MEM);
        } else if (type == SYS_RES_IOPORT) {
                rman_set_bustag(rv, I386_BUS_SPACE_IO);
                rman_set_bushandle(rv, rv->r_start);
        }

        if (needactivate) {
                if (bus_activate_resource(child, type, *rid, rv)) {
                        rman_release_resource(rv);
                        return 0;
                }
        }

        return rv;
}

static int
nexus_activate_resource(device_t bus, device_t child, int type, int rid,
                        struct resource *r)
{
        /*
         * If this is a memory resource, map it into the kernel.
         */
        if (rman_get_bustag(r) == I386_BUS_SPACE_MEM) {
                caddr_t vaddr = 0;

                if (rman_get_end(r) < 1024 * 1024) {
                        /*
                         * The first 1Mb is mapped at KERNBASE.
                         */
                        vaddr = (caddr_t)(uintptr_t)(KERNBASE + rman_get_start(r));
                } else {
                        u_int64_t paddr;
                        u_int64_t psize;
                        u_int32_t poffs;

                        paddr = rman_get_start(r);
                        psize = rman_get_size(r);

                        poffs = paddr - trunc_page(paddr);
                        vaddr = (caddr_t) pmap_mapdev(paddr-poffs, psize+poffs) + poffs;
                }
                rman_set_virtual(r, vaddr);
                /* IBM-PC: the type of bus_space_handle_t is u_int */
                rman_set_bushandle(r, (bus_space_handle_t) vaddr);
        }
        return (rman_activate_resource(r));
}

static int
nexus_deactivate_resource(device_t bus, device_t child, int type, int rid,
                          struct resource *r)
{
        /*
         * If this is a memory resource, unmap it.
         */
        if ((rman_get_bustag(r) == I386_BUS_SPACE_MEM) &&
            (rman_get_end(r) >= 1024 * 1024)) {
                u_int32_t psize;

                psize = rman_get_size(r);
                pmap_unmapdev((vm_offset_t)rman_get_virtual(r), psize);
        }

        return (rman_deactivate_resource(r));
}

static int
nexus_release_resource(device_t bus, device_t child, int type, int rid,
                       struct resource *r)
{
        if (rman_get_flags(r) & RF_ACTIVE) {
                int error = bus_deactivate_resource(child, type, rid, r);
                if (error)
                        return error;
        }
        return (rman_release_resource(r));
}

static int
nexus_config_intr(device_t bus, device_t chile, int irq,
    enum intr_trigger trig, enum intr_polarity pola)
{
        machintr_legacy_intr_config(irq, trig, pola);
        return 0;
}

/*
 * Currently this uses the really grody interface from kern/kern_intr.c
 * (which really doesn't belong in kern/anything.c).  Eventually, all of
 * the code in kern_intr.c and machdep_intr.c should get moved here, since
 * this is going to be the official interface.
 */
static int
nexus_setup_intr(device_t bus, device_t child, struct resource *irq,
    int flags, void (*ihand)(void *), void *arg, void **cookiep,
    lwkt_serialize_t serializer, const char *desc)
{
        int     error, icflags;

        /* somebody tried to setup an irq that failed to allocate! */
        if (irq == NULL)
                panic("%s: NULL irq resource!", __func__);

        *cookiep = NULL;
        icflags = flags;
        if ((irq->r_flags & RF_SHAREABLE) == 0)
                icflags |= INTR_EXCL;

        /*
         * We depend here on rman_activate_resource() being idempotent.
         */
        error = rman_activate_resource(irq);
        if (error)
                return (error);

        /* Use device name, if description is not specified */
        if (desc == NULL)
                desc = device_get_nameunit(child);

        /*
         * XXX cast the interrupt handler function to an inthand2_t.  The
         * difference is that an additional frame argument is passed which
         * we do not currently want to expose the BUS subsystem to.
         */
        *cookiep = register_int(irq->r_start, (inthand2_t *)ihand, arg,
                                desc, serializer, icflags, rman_get_cpuid(irq));
        if (*cookiep == NULL)
                error = EINVAL;
        return (error);
}

static int
nexus_teardown_intr(device_t dev, device_t child, struct resource *r, void *ih)
{
        if (ih) {
                unregister_int(ih, rman_get_cpuid(r));
                return (0);
        }
        return(-1);
}

static int
nexus_set_resource(device_t dev, device_t child, int type, int rid,
    u_long start, u_long count, int cpuid)
{
        struct nexus_device     *ndev = DEVTONX(child);
        struct resource_list    *rl = &ndev->nx_resources;

        /* XXX this should return a success/failure indicator */
        resource_list_add(rl, type, rid, start, start + count - 1, count,
            cpuid);
        return(0);
}

static int
nexus_get_resource(device_t dev, device_t child, int type, int rid, u_long *startp, u_long *countp)
{
        struct nexus_device     *ndev = DEVTONX(child);
        struct resource_list    *rl = &ndev->nx_resources;
        struct resource_list_entry *rle;

        rle = resource_list_find(rl, type, rid);
        device_printf(child, "type %d  rid %d  startp %p  countp %p - got %p\n",
                      type, rid, startp, countp, rle);
        if (!rle)
                return(ENOENT);
        if (startp)
                *startp = rle->start;
        if (countp)
                *countp = rle->count;
        return(0);
}

static void
nexus_delete_resource(device_t dev, device_t child, int type, int rid)
{
        struct nexus_device     *ndev = DEVTONX(child);
        struct resource_list    *rl = &ndev->nx_resources;

        resource_list_delete(rl, type, rid);
}

#if NPCI > 0
static int
nexus_alloc_msi(device_t dev, device_t child, int count, int maxcount,
    int *irqs, int cpuid)
{
        if (!lapic_enable)
                return ENODEV;

        return MachIntrABI.msi_alloc(irqs, count, cpuid);
}

static int
nexus_release_msi(device_t dev, device_t child, int count, int *irqs, int cpuid)
{
        KKASSERT(lapic_enable);
        MachIntrABI.msi_release(irqs, count, cpuid);
        return 0;
}

static int
nexus_map_msi(device_t dev, device_t child, int irq, uint64_t *addr,
    uint32_t *data, int cpuid)
{
        KKASSERT(lapic_enable);
        MachIntrABI.msi_map(irq, addr, data, cpuid);
        return 0;
}

static int
nexus_alloc_msix(device_t dev, device_t child, int *irq, int cpuid)
{
        if (!lapic_enable)
                return ENODEV;

        return MachIntrABI.msix_alloc(irq, cpuid);
}

static int
nexus_release_msix(device_t dev, device_t child, int irq, int cpuid)
{
        KKASSERT(lapic_enable);
        MachIntrABI.msix_release(irq, cpuid);
        return 0;
}
#endif

/* Placeholder for system RAM. */
static void
ram_identify(driver_t *driver, device_t parent)
{
        if (resource_disabled("ram", 0))
                return;
        if (BUS_ADD_CHILD(parent, parent, 0, "ram", 0) == NULL)
                panic("%s", __func__);
}

static int
ram_probe(device_t dev)
{
        device_quiet(dev);
        device_set_desc(dev, "System RAM");
        return (0);
}

static int
ram_attach(device_t dev)
{
        struct bios_smap *smapbase, *smap, *smapend;
        struct resource *res;
        vm_phystable_t *p;
        caddr_t kmdp;
        uint32_t smapsize;
        int error, rid;

        device_quiet(dev);
        device_set_desc(dev, "System RAM");

        /* Retrieve the system memory map from the loader. */
        kmdp = preload_search_by_type("elf kernel");
        if (kmdp == NULL)
                kmdp = preload_search_by_type(ELF_KERN_STR);
        if (kmdp != NULL)
                smapbase = (struct bios_smap *)preload_search_info(kmdp,
                    MODINFO_METADATA | MODINFOMD_SMAP);
        else
                smapbase = NULL;
        if (smapbase != NULL) {
                smapsize = *((u_int32_t *)smapbase - 1);
                smapend = (struct bios_smap *)((uintptr_t)smapbase + smapsize);

                rid = 0;
                for (smap = smapbase; smap < smapend; smap++) {
                        if (smap->type != SMAP_TYPE_MEMORY ||
                            smap->length == 0)
                                continue;
                        error = bus_set_resource(dev, SYS_RES_MEMORY, rid,
                            smap->base, smap->length, -1);
                        if (error)
                                panic("%s: resource %d failed set with %d",
                                    __func__, rid, error);
                        res = bus_alloc_resource_any(dev, SYS_RES_MEMORY, &rid,
                            0);
                        if (res == NULL) {
                                panic("%s: resource %d failed to "
                                      "attach 0x%016jx/%jd",
                                    __func__, rid,
                                    (intmax_t)smap->base,
                                    (intmax_t)smap->length);
                        }
                        rid++;
                }
                return (0);
        }

        /*
         * If the system map is not available, fall back to using
         * dump_avail[].  We use the dump_avail[] array rather than
         * phys_avail[] for the memory map as phys_avail[] contains
         * holes for kernel memory, page 0, the message buffer, and
         * the dcons buffer.  We test the end address in the loop
         * instead of the start since the start address for the first
         * segment is 0.
         */
        for (rid = 0, p = &dump_avail[0]; p->phys_end; ++rid, ++p) {
                error = bus_set_resource(dev, SYS_RES_MEMORY, rid,
                                         p->phys_beg,
                                         p->phys_end - p->phys_beg,
                                         -1);
                if (error)
                        panic("%s: resource %d failed set with %d", __func__,
                              rid, error);
                res = bus_alloc_resource_any(dev, SYS_RES_MEMORY, &rid, 0);
                if (res == NULL)
                        panic("%s: resource %d failed to attach", __func__,
                              rid);
        }
        return (0);
}
static device_method_t ram_methods[] = {
        /* Device interface */
        DEVMETHOD(device_identify,      ram_identify),
        DEVMETHOD(device_probe,         ram_probe),
        DEVMETHOD(device_attach,        ram_attach),
        { 0, 0 }
};

static driver_t ram_driver = {
        "ram",
        ram_methods,
        1,              /* no softc */
};

static devclass_t ram_devclass;
DRIVER_MODULE(ram, nexus, ram_driver, ram_devclass, NULL, NULL);