busdma: Add bus_dmamap_load_ccb; ease driver porting from FreeBSD.

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

/*
 * Copyright (c) 1997, 1998 Justin T. Gibbs.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions, and the following disclaimer,
 *    without modification, immediately at the beginning of the file.
 * 2. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS 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/busdma_machdep.c,v 1.94 2008/08/15 20:51:31 kmacy Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/uio.h>
#include <sys/bus_dma.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/lock.h>

#include <sys/thread2.h>
#include <sys/spinlock2.h>
#include <sys/mplock2.h>

#include <vm/vm.h>
#include <vm/vm_page.h>

/* XXX needed for to access pmap to convert per-proc virtual to physical */
#include <sys/proc.h>
#include <vm/vm_map.h>

#include <machine/md_var.h>

#include <bus/cam/cam.h>
#include <bus/cam/cam_ccb.h>

#define MAX_BPAGES      1024

/*
 * 16 x N declared on stack.
 */
#define BUS_DMA_CACHE_SEGMENTS  8

struct bounce_zone;
struct bus_dmamap;

struct bus_dma_tag {
        bus_dma_tag_t   parent;
        bus_size_t      alignment;
        bus_size_t      boundary;
        bus_addr_t      lowaddr;
        bus_addr_t      highaddr;
        bus_dma_filter_t *filter;
        void            *filterarg;
        bus_size_t      maxsize;
        u_int           nsegments;
        bus_size_t      maxsegsz;
        int             flags;
        int             ref_count;
        int             map_count;
        bus_dma_segment_t *segments;
        struct bounce_zone *bounce_zone;
        struct spinlock spin;
};

/*
 * bus_dma_tag private flags
 */
#define BUS_DMA_BOUNCE_ALIGN    BUS_DMA_BUS2
#define BUS_DMA_BOUNCE_LOWADDR  BUS_DMA_BUS3
#define BUS_DMA_MIN_ALLOC_COMP  BUS_DMA_BUS4

#define BUS_DMA_COULD_BOUNCE    (BUS_DMA_BOUNCE_LOWADDR | BUS_DMA_BOUNCE_ALIGN)

#define BUS_DMAMEM_KMALLOC(dmat) \
        ((dmat)->maxsize <= PAGE_SIZE && \
         (dmat)->alignment <= PAGE_SIZE && \
         (dmat)->lowaddr >= ptoa(Maxmem))

struct bounce_page {
        vm_offset_t     vaddr;          /* kva of bounce buffer */
        bus_addr_t      busaddr;        /* Physical address */
        vm_offset_t     datavaddr;      /* kva of client data */
        bus_size_t      datacount;      /* client data count */
        STAILQ_ENTRY(bounce_page) links;
};

struct bounce_zone {
        STAILQ_ENTRY(bounce_zone) links;
        STAILQ_HEAD(bp_list, bounce_page) bounce_page_list;
        STAILQ_HEAD(, bus_dmamap) bounce_map_waitinglist;
        struct spinlock spin;
        int             total_bpages;
        int             free_bpages;
        int             reserved_bpages;
        int             active_bpages;
        int             total_bounced;
        int             total_deferred;
        int             reserve_failed;
        bus_size_t      alignment;
        bus_addr_t      lowaddr;
        char            zoneid[8];
        char            lowaddrid[20];
        struct sysctl_ctx_list sysctl_ctx;
        struct sysctl_oid *sysctl_tree;
};

#define BZ_LOCK(bz)     spin_lock(&(bz)->spin)
#define BZ_UNLOCK(bz)   spin_unlock(&(bz)->spin)

static struct lwkt_token bounce_zone_tok =
        LWKT_TOKEN_INITIALIZER(bounce_zone_token);
static int busdma_zonecount;
static STAILQ_HEAD(, bounce_zone) bounce_zone_list =
        STAILQ_HEAD_INITIALIZER(bounce_zone_list);

static int busdma_priv_zonecount = -1;

int busdma_swi_pending;
static int total_bounce_pages;
static int max_bounce_pages = MAX_BPAGES;
static int bounce_alignment = 1; /* XXX temporary */

TUNABLE_INT("hw.busdma.max_bpages", &max_bounce_pages);
TUNABLE_INT("hw.busdma.bounce_alignment", &bounce_alignment);

struct bus_dmamap {
        struct bp_list  bpages;
        int             pagesneeded;
        int             pagesreserved;
        bus_dma_tag_t   dmat;
        void            *buf;           /* unmapped buffer pointer */
        bus_size_t      buflen;         /* unmapped buffer length */
        bus_dmamap_callback_t *callback;
        void            *callback_arg;
        STAILQ_ENTRY(bus_dmamap) links;
};

static STAILQ_HEAD(, bus_dmamap) bounce_map_callbacklist =
        STAILQ_HEAD_INITIALIZER(bounce_map_callbacklist);
static struct spinlock bounce_map_list_spin =
        SPINLOCK_INITIALIZER(&bounce_map_list_spin, "bounce_map_list_spin");

static struct bus_dmamap nobounce_dmamap;

static int              alloc_bounce_zone(bus_dma_tag_t);
static int              alloc_bounce_pages(bus_dma_tag_t, u_int, int);
static void             free_bounce_pages_all(bus_dma_tag_t);
static void             free_bounce_zone(bus_dma_tag_t);
static int              reserve_bounce_pages(bus_dma_tag_t, bus_dmamap_t, int);
static void             return_bounce_pages(bus_dma_tag_t, bus_dmamap_t);
static bus_addr_t       add_bounce_page(bus_dma_tag_t, bus_dmamap_t,
                            vm_offset_t, bus_size_t *);
static void             free_bounce_page(bus_dma_tag_t, struct bounce_page *);

static bus_dmamap_t     get_map_waiting(bus_dma_tag_t);
static void             add_map_callback(bus_dmamap_t);

SYSCTL_NODE(_hw, OID_AUTO, busdma, CTLFLAG_RD, 0, "Busdma parameters");
SYSCTL_INT(_hw_busdma, OID_AUTO, total_bpages, CTLFLAG_RD, &total_bounce_pages,
           0, "Total bounce pages");
SYSCTL_INT(_hw_busdma, OID_AUTO, max_bpages, CTLFLAG_RD, &max_bounce_pages,
           0, "Max bounce pages per bounce zone");
SYSCTL_INT(_hw_busdma, OID_AUTO, bounce_alignment, CTLFLAG_RD,
           &bounce_alignment, 0, "Obey alignment constraint");

static __inline int
run_filter(bus_dma_tag_t dmat, bus_addr_t paddr)
{
        int retval;

        retval = 0;
        do {
                if (((paddr > dmat->lowaddr && paddr <= dmat->highaddr) ||
                     (bounce_alignment && (paddr & (dmat->alignment - 1)) != 0))
                 && (dmat->filter == NULL ||
                     dmat->filter(dmat->filterarg, paddr) != 0))
                        retval = 1;

                dmat = dmat->parent;
        } while (retval == 0 && dmat != NULL);
        return (retval);
}

static __inline
bus_dma_segment_t *
bus_dma_tag_lock(bus_dma_tag_t tag, bus_dma_segment_t *cache)
{
        if (tag->flags & BUS_DMA_PROTECTED)
                return(tag->segments);

        if (tag->nsegments <= BUS_DMA_CACHE_SEGMENTS)
                return(cache);
        spin_lock(&tag->spin);
        return(tag->segments);
}

static __inline
void
bus_dma_tag_unlock(bus_dma_tag_t tag)
{
        if (tag->flags & BUS_DMA_PROTECTED)
                return;

        if (tag->nsegments > BUS_DMA_CACHE_SEGMENTS)
                spin_unlock(&tag->spin);
}

/*
 * Allocate a device specific dma_tag.
 */
int
bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
                   bus_size_t boundary, bus_addr_t lowaddr,
                   bus_addr_t highaddr, bus_dma_filter_t *filter,
                   void *filterarg, bus_size_t maxsize, int nsegments,
                   bus_size_t maxsegsz, int flags, bus_dma_tag_t *dmat)
{
        bus_dma_tag_t newtag;
        int error = 0;

        /*
         * Sanity checks
         */

        if (alignment == 0)
                alignment = 1;
        if (alignment & (alignment - 1))
                panic("alignment must be power of 2");

        if (boundary != 0) {
                if (boundary & (boundary - 1))
                        panic("boundary must be power of 2");
                if (boundary < maxsegsz) {
                        kprintf("boundary < maxsegsz:\n");
                        print_backtrace(-1);
                        maxsegsz = boundary;
                }
        }

        /* Return a NULL tag on failure */
        *dmat = NULL;

        newtag = kmalloc(sizeof(*newtag), M_DEVBUF, M_INTWAIT | M_ZERO);

        spin_init(&newtag->spin, "busdmacreate");
        newtag->parent = parent;
        newtag->alignment = alignment;
        newtag->boundary = boundary;
        newtag->lowaddr = trunc_page((vm_paddr_t)lowaddr) + (PAGE_SIZE - 1);
        newtag->highaddr = trunc_page((vm_paddr_t)highaddr) + (PAGE_SIZE - 1);
        newtag->filter = filter;
        newtag->filterarg = filterarg;
        newtag->maxsize = maxsize;
        newtag->nsegments = nsegments;
        newtag->maxsegsz = maxsegsz;
        newtag->flags = flags;
        newtag->ref_count = 1; /* Count ourself */
        newtag->map_count = 0;
        newtag->segments = NULL;
        newtag->bounce_zone = NULL;

        /* Take into account any restrictions imposed by our parent tag */
        if (parent != NULL) {
                newtag->lowaddr = MIN(parent->lowaddr, newtag->lowaddr);
                newtag->highaddr = MAX(parent->highaddr, newtag->highaddr);

                if (newtag->boundary == 0) {
                        newtag->boundary = parent->boundary;
                } else if (parent->boundary != 0) {
                        newtag->boundary = MIN(parent->boundary,
                                               newtag->boundary);
                }

#ifdef notyet
                newtag->alignment = MAX(parent->alignment, newtag->alignment);
#endif

                if (newtag->filter == NULL) {
                        /*
                         * Short circuit looking at our parent directly
                         * since we have encapsulated all of its information
                         */
                        newtag->filter = parent->filter;
                        newtag->filterarg = parent->filterarg;
                        newtag->parent = parent->parent;
                }
                if (newtag->parent != NULL)
                        parent->ref_count++;
        }

        if (newtag->lowaddr < ptoa(Maxmem))
                newtag->flags |= BUS_DMA_BOUNCE_LOWADDR;
        if (bounce_alignment && newtag->alignment > 1 &&
            !(newtag->flags & BUS_DMA_ALIGNED))
                newtag->flags |= BUS_DMA_BOUNCE_ALIGN;

        if ((newtag->flags & BUS_DMA_COULD_BOUNCE) &&
            (flags & BUS_DMA_ALLOCNOW) != 0) {
                struct bounce_zone *bz;

                /* Must bounce */

                error = alloc_bounce_zone(newtag);
                if (error)
                        goto back;
                bz = newtag->bounce_zone;

                if ((newtag->flags & BUS_DMA_ALLOCALL) == 0 &&
                    ptoa(bz->total_bpages) < maxsize) {
                        int pages;

                        if (flags & BUS_DMA_ONEBPAGE) {
                                pages = 1;
                        } else {
                                pages = atop(round_page(maxsize)) -
                                        bz->total_bpages;
                                pages = MAX(pages, 1);
                        }

                        /* Add pages to our bounce pool */
                        if (alloc_bounce_pages(newtag, pages, flags) < pages)
                                error = ENOMEM;

                        /* Performed initial allocation */
                        newtag->flags |= BUS_DMA_MIN_ALLOC_COMP;
                }
        }
back:
        if (error) {
                free_bounce_zone(newtag);
                kfree(newtag, M_DEVBUF);
        } else {
                *dmat = newtag;
        }
        return error;
}

int
bus_dma_tag_destroy(bus_dma_tag_t dmat)
{
        if (dmat != NULL) {
                if (dmat->map_count != 0)
                        return (EBUSY);

                while (dmat != NULL) {
                        bus_dma_tag_t parent;

                        parent = dmat->parent;
                        dmat->ref_count--;
                        if (dmat->ref_count == 0) {
                                free_bounce_zone(dmat);
                                if (dmat->segments != NULL)
                                        kfree(dmat->segments, M_DEVBUF);
                                kfree(dmat, M_DEVBUF);
                                /*
                                 * Last reference count, so
                                 * release our reference
                                 * count on our parent.
                                 */
                                dmat = parent;
                        } else
                                dmat = NULL;
                }
        }
        return (0);
}

bus_size_t
bus_dma_tag_getmaxsize(bus_dma_tag_t tag)
{
        return(tag->maxsize);
}

/*
 * Allocate a handle for mapping from kva/uva/physical
 * address space into bus device space.
 */
int
bus_dmamap_create(bus_dma_tag_t dmat, int flags, bus_dmamap_t *mapp)
{
        int error;

        error = 0;

        if (dmat->segments == NULL) {
                KKASSERT(dmat->nsegments && dmat->nsegments < 16384);
                dmat->segments = kmalloc(sizeof(bus_dma_segment_t) * 
                                        dmat->nsegments, M_DEVBUF, M_INTWAIT);
        }

        if (dmat->flags & BUS_DMA_COULD_BOUNCE) {
                struct bounce_zone *bz;
                int maxpages;

                /* Must bounce */

                if (dmat->bounce_zone == NULL) {
                        error = alloc_bounce_zone(dmat);
                        if (error)
                                return error;
                }
                bz = dmat->bounce_zone;

                *mapp = kmalloc(sizeof(**mapp), M_DEVBUF, M_INTWAIT | M_ZERO);

                /* Initialize the new map */
                STAILQ_INIT(&((*mapp)->bpages));

                /*
                 * Attempt to add pages to our pool on a per-instance
                 * basis up to a sane limit.
                 */
                if (dmat->flags & BUS_DMA_ALLOCALL) {
                        maxpages = Maxmem - atop(dmat->lowaddr);
                } else if (dmat->flags & BUS_DMA_BOUNCE_ALIGN) {
                        maxpages = max_bounce_pages;
                } else {
                        maxpages = MIN(max_bounce_pages,
                                       Maxmem - atop(dmat->lowaddr));
                }
                if ((dmat->flags & BUS_DMA_MIN_ALLOC_COMP) == 0 ||
                    (dmat->map_count > 0 && bz->total_bpages < maxpages)) {
                        int pages;

                        if (flags & BUS_DMA_ONEBPAGE) {
                                pages = 1;
                        } else {
                                pages = atop(round_page(dmat->maxsize));
                                pages = MIN(maxpages - bz->total_bpages, pages);
                                pages = MAX(pages, 1);
                        }
                        if (alloc_bounce_pages(dmat, pages, flags) < pages)
                                error = ENOMEM;

                        if ((dmat->flags & BUS_DMA_MIN_ALLOC_COMP) == 0) {
                                if (!error &&
                                    (dmat->flags & BUS_DMA_ALLOCALL) == 0)
                                        dmat->flags |= BUS_DMA_MIN_ALLOC_COMP;
                        } else {
                                error = 0;
                        }
                }
        } else {
                *mapp = NULL;
        }
        if (!error) {
                dmat->map_count++;
        } else {
                kfree(*mapp, M_DEVBUF);
                *mapp = NULL;
        }
        return error;
}

/*
 * Destroy a handle for mapping from kva/uva/physical
 * address space into bus device space.
 */
int
bus_dmamap_destroy(bus_dma_tag_t dmat, bus_dmamap_t map)
{
        if (map != NULL) {
                if (STAILQ_FIRST(&map->bpages) != NULL)
                        return (EBUSY);
                kfree(map, M_DEVBUF);
        }
        dmat->map_count--;
        return (0);
}

static __inline bus_size_t
check_kmalloc(bus_dma_tag_t dmat, const void *vaddr0, int verify)
{
        bus_size_t maxsize = 0;
        uintptr_t vaddr = (uintptr_t)vaddr0;

        if ((vaddr ^ (vaddr + dmat->maxsize - 1)) & ~PAGE_MASK) {
                if (verify)
                        panic("boundary check failed\n");
                if (bootverbose)
                        kprintf("boundary check failed\n");
                maxsize = dmat->maxsize;
        }
        if (vaddr & (dmat->alignment - 1)) {
                if (verify)
                        panic("alignment check failed\n");
                if (bootverbose)
                        kprintf("alignment check failed\n");
                if (dmat->maxsize < dmat->alignment)
                        maxsize = dmat->alignment;
                else
                        maxsize = dmat->maxsize;
        }
        return maxsize;
}

/*
 * Allocate a piece of memory that can be efficiently mapped into
 * bus device space based on the constraints lited in the dma tag.
 *
 * mapp is degenerate.  By definition this allocation should not require
 * bounce buffers so do not allocate a dma map.
 */
int
bus_dmamem_alloc(bus_dma_tag_t dmat, void **vaddr, int flags,
                 bus_dmamap_t *mapp)
{
        vm_memattr_t attr;
        int mflags;

        /* If we succeed, no mapping/bouncing will be required */
        *mapp = NULL;

        if (dmat->segments == NULL) {
                KKASSERT(dmat->nsegments < 16384);
                dmat->segments = kmalloc(sizeof(bus_dma_segment_t) * 
                                        dmat->nsegments, M_DEVBUF, M_INTWAIT);
        }

        if (flags & BUS_DMA_NOWAIT)
                mflags = M_NOWAIT;
        else
                mflags = M_WAITOK;
        if (flags & BUS_DMA_ZERO)
                mflags |= M_ZERO;
        if (flags & BUS_DMA_NOCACHE)
                attr = VM_MEMATTR_UNCACHEABLE;
        else
                attr = VM_MEMATTR_DEFAULT;

        /* XXX must alloc with correct mem attribute here */
        if (BUS_DMAMEM_KMALLOC(dmat)) {
                bus_size_t maxsize;

                *vaddr = kmalloc(dmat->maxsize, M_DEVBUF, mflags);

                /*
                 * XXX
                 * Check whether the allocation
                 * - crossed a page boundary
                 * - was not aligned
                 * Retry with power-of-2 alignment in the above cases.
                 */
                maxsize = check_kmalloc(dmat, *vaddr, 0);
                if (maxsize) {
                        kfree(*vaddr, M_DEVBUF);
                        *vaddr = kmalloc(maxsize, M_DEVBUF,
                            mflags | M_POWEROF2);
                        check_kmalloc(dmat, *vaddr, 1);
                }
        } else {
                /*
                 * XXX Use Contigmalloc until it is merged into this facility
                 *     and handles multi-seg allocations.  Nobody is doing
                 *     multi-seg allocations yet though.
                 */
                *vaddr = contigmalloc(dmat->maxsize, M_DEVBUF, mflags,
                    0ul, dmat->lowaddr, dmat->alignment, dmat->boundary);
        }
        if (*vaddr == NULL)
                return (ENOMEM);

        if (attr != VM_MEMATTR_DEFAULT)
                pmap_change_attr((vm_offset_t)(*vaddr), dmat->maxsize / PAGE_SIZE, attr);
        return (0);
}

/*
 * Free a piece of memory and it's allociated dmamap, that was allocated
 * via bus_dmamem_alloc.  Make the same choice for free/contigfree.
 */
void
bus_dmamem_free(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map)
{
        /*
         * dmamem does not need to be bounced, so the map should be
         * NULL
         */
        if (map != NULL)
                panic("bus_dmamem_free: Invalid map freed");
        if (BUS_DMAMEM_KMALLOC(dmat))
                kfree(vaddr, M_DEVBUF);
        else
                contigfree(vaddr, dmat->maxsize, M_DEVBUF);
}

static __inline vm_paddr_t
_bus_dma_extract(pmap_t pmap, vm_offset_t vaddr)
{
        if (pmap)
                return pmap_extract(pmap, vaddr, NULL);
        else
                return pmap_kextract(vaddr);
}

/*
 * Utility function to load a linear buffer.  lastaddrp holds state
 * between invocations (for multiple-buffer loads).  segp contains
 * the segment following the starting one on entrace, and the ending
 * segment on exit.  first indicates if this is the first invocation
 * of this function.
 */
static int
_bus_dmamap_load_buffer(bus_dma_tag_t dmat,
                        bus_dmamap_t map,
                        void *buf, bus_size_t buflen,
                        bus_dma_segment_t *segments,
                        int nsegments,
                        pmap_t pmap,
                        int flags,
                        vm_paddr_t *lastpaddrp,
                        int *segp,
                        int first)
{
        vm_offset_t vaddr;
        vm_paddr_t paddr, nextpaddr;
        bus_dma_segment_t *sg;
        bus_addr_t bmask;
        int seg, error = 0;

        if (map == NULL)
                map = &nobounce_dmamap;

#ifdef INVARIANTS
        if (dmat->flags & BUS_DMA_ALIGNED)
                KKASSERT(((uintptr_t)buf & (dmat->alignment - 1)) == 0);
#endif

        /*
         * If we are being called during a callback, pagesneeded will
         * be non-zero, so we can avoid doing the work twice.
         */
        if ((dmat->flags & BUS_DMA_COULD_BOUNCE) &&
            map != &nobounce_dmamap && map->pagesneeded == 0) {
                vm_offset_t vendaddr;

                /*
                 * Count the number of bounce pages
                 * needed in order to complete this transfer
                 */
                vaddr = (vm_offset_t)buf;
                vendaddr = (vm_offset_t)buf + buflen;

                while (vaddr < vendaddr) {
                        paddr = _bus_dma_extract(pmap, vaddr);
                        if (run_filter(dmat, paddr) != 0)
                                map->pagesneeded++;
                        vaddr += (PAGE_SIZE - (vaddr & PAGE_MASK));
                }
        }

        /* Reserve Necessary Bounce Pages */
        if (map->pagesneeded != 0) {
                struct bounce_zone *bz;

                bz = dmat->bounce_zone;
                BZ_LOCK(bz);
                if (flags & BUS_DMA_NOWAIT) {
                        if (reserve_bounce_pages(dmat, map, 0) != 0) {
                                BZ_UNLOCK(bz);
                                error = ENOMEM;
                                goto free_bounce;
                        }
                } else {
                        if (reserve_bounce_pages(dmat, map, 1) != 0) {
                                /* Queue us for resources */
                                map->dmat = dmat;
                                map->buf = buf;
                                map->buflen = buflen;

                                STAILQ_INSERT_TAIL(
                                    &dmat->bounce_zone->bounce_map_waitinglist,
                                    map, links);
                                BZ_UNLOCK(bz);

                                return (EINPROGRESS);
                        }
                }
                BZ_UNLOCK(bz);
        }

        KKASSERT(*segp >= 1 && *segp <= nsegments);
        seg = *segp;
        sg = &segments[seg - 1];

        vaddr = (vm_offset_t)buf;
        nextpaddr = *lastpaddrp;
        bmask = ~(dmat->boundary - 1);  /* note: will be 0 if boundary is 0 */

        /* force at least one segment */
        do {
                bus_size_t size;

                /*
                 * Per-page main loop
                 */
                paddr = _bus_dma_extract(pmap, vaddr);
                size = PAGE_SIZE - (paddr & PAGE_MASK);
                if (size > buflen)
                        size = buflen;
                if (map->pagesneeded != 0 && run_filter(dmat, paddr)) {
                        /*
                         * NOTE: paddr may have different in-page offset,
                         *       unless BUS_DMA_KEEP_PG_OFFSET is set.
                         */
                        paddr = add_bounce_page(dmat, map, vaddr, &size);
                }

                /*
                 * Fill in the bus_dma_segment
                 */
                if (first) {
                        sg->ds_addr = paddr;
                        sg->ds_len = size;
                        first = 0;
                } else if (paddr == nextpaddr) {
                        sg->ds_len += size;
                } else {
                        sg++;
                        seg++;
                        if (seg > nsegments)
                                break;
                        sg->ds_addr = paddr;
                        sg->ds_len = size;
                }
                nextpaddr = paddr + size;

                /*
                 * Handle maxsegsz and boundary issues with a nested loop
                 */
                for (;;) {
                        bus_size_t tmpsize;

                        /*
                         * Limit to the boundary and maximum segment size
                         */
                        if (((nextpaddr - 1) ^ sg->ds_addr) & bmask) {
                                tmpsize = dmat->boundary -
                                          (sg->ds_addr & ~bmask);
                                if (tmpsize > dmat->maxsegsz)
                                        tmpsize = dmat->maxsegsz;
                                KKASSERT(tmpsize < sg->ds_len);
                        } else if (sg->ds_len > dmat->maxsegsz) {
                                tmpsize = dmat->maxsegsz;
                        } else {
                                break;
                        }

                        /*
                         * Futz, split the data into a new segment.
                         */
                        if (seg >= nsegments)
                                goto fail;
                        sg[1].ds_len = sg[0].ds_len - tmpsize;
                        sg[1].ds_addr = sg[0].ds_addr + tmpsize;
                        sg[0].ds_len = tmpsize;
                        sg++;
                        seg++;
                }

                /*
                 * Adjust for loop
                 */
                buflen -= size;
                vaddr += size;
        } while (buflen > 0);
fail:
        if (buflen != 0)
                error = EFBIG;

        *segp = seg;
        *lastpaddrp = nextpaddr;

free_bounce:
        if (error && (dmat->flags & BUS_DMA_COULD_BOUNCE) &&
            map != &nobounce_dmamap) {
                _bus_dmamap_unload(dmat, map);
                return_bounce_pages(dmat, map);
        }
        return error;
}

/*
 * Map the buffer buf into bus space using the dmamap map.
 */
int
bus_dmamap_load(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
                bus_size_t buflen, bus_dmamap_callback_t *callback,
                void *callback_arg, int flags)
{
        bus_dma_segment_t cache_segments[BUS_DMA_CACHE_SEGMENTS];
        bus_dma_segment_t *segments;
        vm_paddr_t lastaddr = 0;
        int error, nsegs = 1;

        if (map != NULL) {
                /*
                 * XXX
                 * Follow old semantics.  Once all of the callers are fixed,
                 * we should get rid of these internal flag "adjustment".
                 */
                flags &= ~BUS_DMA_NOWAIT;
                flags |= BUS_DMA_WAITOK;

                map->callback = callback;
                map->callback_arg = callback_arg;
        }

        segments = bus_dma_tag_lock(dmat, cache_segments);
        error = _bus_dmamap_load_buffer(dmat, map, buf, buflen,
                        segments, dmat->nsegments,
                        NULL, flags, &lastaddr, &nsegs, 1);
        if (error == EINPROGRESS) {
                KKASSERT((dmat->flags &
                          (BUS_DMA_PRIVBZONE | BUS_DMA_ALLOCALL)) !=
                         (BUS_DMA_PRIVBZONE | BUS_DMA_ALLOCALL));

                if (dmat->flags & BUS_DMA_PROTECTED)
                        panic("protected dmamap callback will be defered");

                bus_dma_tag_unlock(dmat);
                return error;
        }
        callback(callback_arg, segments, nsegs, error);
        bus_dma_tag_unlock(dmat);
        return 0;
}

int
bus_dmamap_load_ccb(bus_dma_tag_t dmat, bus_dmamap_t map, union ccb *ccb,
    bus_dmamap_callback_t *callback, void *callback_arg, int flags)
{
        const struct ccb_scsiio *csio;

        KASSERT(ccb->ccb_h.func_code == XPT_SCSI_IO ||
            ccb->ccb_h.func_code == XPT_CONT_TARGET_IO,
            ("invalid ccb func_code %u", ccb->ccb_h.func_code));
        csio = &ccb->csio;

        return (bus_dmamap_load(dmat, map, csio->data_ptr, csio->dxfer_len,
            callback, callback_arg, flags));
}

/*
 * Like _bus_dmamap_load(), but for mbufs.
 */
int
bus_dmamap_load_mbuf(bus_dma_tag_t dmat, bus_dmamap_t map,
                     struct mbuf *m0,
                     bus_dmamap_callback2_t *callback, void *callback_arg,
                     int flags)
{
        bus_dma_segment_t cache_segments[BUS_DMA_CACHE_SEGMENTS];
        bus_dma_segment_t *segments;
        int nsegs, error;

        /*
         * XXX
         * Follow old semantics.  Once all of the callers are fixed,
         * we should get rid of these internal flag "adjustment".
         */
        flags &= ~BUS_DMA_WAITOK;
        flags |= BUS_DMA_NOWAIT;

        segments = bus_dma_tag_lock(dmat, cache_segments);
        error = bus_dmamap_load_mbuf_segment(dmat, map, m0,
                        segments, dmat->nsegments, &nsegs, flags);
        if (error) {
                /* force "no valid mappings" in callback */
                callback(callback_arg, segments, 0,
                         0, error);
        } else {
                callback(callback_arg, segments, nsegs,
                         m0->m_pkthdr.len, error);
        }
        bus_dma_tag_unlock(dmat);
        return error;
}

int
bus_dmamap_load_mbuf_segment(bus_dma_tag_t dmat, bus_dmamap_t map,
                             struct mbuf *m0,
                             bus_dma_segment_t *segs, int maxsegs,
                             int *nsegs, int flags)
{
        int error;

        M_ASSERTPKTHDR(m0);

        KASSERT(maxsegs >= 1, ("invalid maxsegs %d", maxsegs));
        KASSERT(maxsegs <= dmat->nsegments,
                ("%d too many segments, dmat only supports %d segments",
                 maxsegs, dmat->nsegments));
        KASSERT(flags & BUS_DMA_NOWAIT,
                ("only BUS_DMA_NOWAIT is supported"));

        if (m0->m_pkthdr.len <= dmat->maxsize) {
                int first = 1;
                vm_paddr_t lastaddr = 0;
                struct mbuf *m;

                *nsegs = 1;
                error = 0;
                for (m = m0; m != NULL && error == 0; m = m->m_next) {
                        if (m->m_len == 0)
                                continue;

                        error = _bus_dmamap_load_buffer(dmat, map,
                                        m->m_data, m->m_len,
                                        segs, maxsegs,
                                        NULL, flags, &lastaddr,
                                        nsegs, first);
                        if (error == ENOMEM && !first) {
                                /*
                                 * Out of bounce pages due to too many
                                 * fragments in the mbuf chain; return
                                 * EFBIG instead.
                                 */
                                error = EFBIG;
                                break;
                        }
                        first = 0;
                }
#ifdef INVARIANTS
                if (!error)
                        KKASSERT(*nsegs <= maxsegs && *nsegs >= 1);
#endif
        } else {
                *nsegs = 0;
                error = EINVAL;
        }
        KKASSERT(error != EINPROGRESS);
        return error;
}

/*
 * Like _bus_dmamap_load(), but for uios.
 */
int
bus_dmamap_load_uio(bus_dma_tag_t dmat, bus_dmamap_t map,
                    struct uio *uio,
                    bus_dmamap_callback2_t *callback, void *callback_arg,
                    int flags)
{
        vm_paddr_t lastaddr;
        int nsegs, error, first, i;
        bus_size_t resid;
        struct iovec *iov;
        pmap_t pmap;
        bus_dma_segment_t cache_segments[BUS_DMA_CACHE_SEGMENTS];
        bus_dma_segment_t *segments;
        bus_dma_segment_t *segs;
        int nsegs_left;

        if (dmat->nsegments <= BUS_DMA_CACHE_SEGMENTS)
                segments = cache_segments;
        else
                segments = kmalloc(sizeof(bus_dma_segment_t) * dmat->nsegments,
                                   M_DEVBUF, M_WAITOK | M_ZERO);

        /*
         * XXX
         * Follow old semantics.  Once all of the callers are fixed,
         * we should get rid of these internal flag "adjustment".
         */
        flags &= ~BUS_DMA_WAITOK;
        flags |= BUS_DMA_NOWAIT;

        resid = (bus_size_t)uio->uio_resid;
        iov = uio->uio_iov;

        segs = segments;
        nsegs_left = dmat->nsegments;

        if (uio->uio_segflg == UIO_USERSPACE) {
                struct thread *td;

                td = uio->uio_td;
                KASSERT(td != NULL && td->td_proc != NULL,
                        ("bus_dmamap_load_uio: USERSPACE but no proc"));
                pmap = vmspace_pmap(td->td_proc->p_vmspace);
        } else {
                pmap = NULL;
        }

        error = 0;
        nsegs = 1;
        first = 1;
        lastaddr = 0;
        for (i = 0; i < uio->uio_iovcnt && resid != 0 && !error; i++) {
                /*
                 * Now at the first iovec to load.  Load each iovec
                 * until we have exhausted the residual count.
                 */
                bus_size_t minlen =
                        resid < iov[i].iov_len ? resid : iov[i].iov_len;
                caddr_t addr = (caddr_t) iov[i].iov_base;

                error = _bus_dmamap_load_buffer(dmat, map, addr, minlen,
                                segs, nsegs_left,
                                pmap, flags, &lastaddr, &nsegs, first);
                first = 0;

                resid -= minlen;
                if (error == 0) {
                        nsegs_left -= nsegs;
                        segs += nsegs;
                }
        }

        /*
         * Minimum one DMA segment, even if 0-length buffer.
         */
        if (nsegs_left == dmat->nsegments)
                --nsegs_left;

        if (error) {
                /* force "no valid mappings" in callback */
                callback(callback_arg, segments, 0,
                         0, error);
        } else {
                callback(callback_arg, segments, dmat->nsegments - nsegs_left,
                         (bus_size_t)uio->uio_resid, error);
        }
        if (dmat->nsegments > BUS_DMA_CACHE_SEGMENTS)
                kfree(segments, M_DEVBUF);
        return error;
}

/*
 * Release the mapping held by map.
 */
void
_bus_dmamap_unload(bus_dma_tag_t dmat, bus_dmamap_t map)
{
        struct bounce_page *bpage;

        while ((bpage = STAILQ_FIRST(&map->bpages)) != NULL) {
                STAILQ_REMOVE_HEAD(&map->bpages, links);
                free_bounce_page(dmat, bpage);
        }
}

void
_bus_dmamap_sync(bus_dma_tag_t dmat, bus_dmamap_t map, bus_dmasync_op_t op)
{
        struct bounce_page *bpage;

        if ((bpage = STAILQ_FIRST(&map->bpages)) != NULL) {
                /*
                 * Handle data bouncing.  We might also
                 * want to add support for invalidating
                 * the caches on broken hardware
                 */
                if (op & BUS_DMASYNC_PREWRITE) {
                        while (bpage != NULL) {
                                bcopy((void *)bpage->datavaddr,
                                      (void *)bpage->vaddr,
                                      bpage->datacount);
                                bpage = STAILQ_NEXT(bpage, links);
                        }
                        cpu_sfence();
                        dmat->bounce_zone->total_bounced++;
                }
                if (op & BUS_DMASYNC_POSTREAD) {
                        cpu_lfence();
                        while (bpage != NULL) {
                                bcopy((void *)bpage->vaddr,
                                      (void *)bpage->datavaddr,
                                      bpage->datacount);
                                bpage = STAILQ_NEXT(bpage, links);
                        }
                        dmat->bounce_zone->total_bounced++;
                }
                /* BUS_DMASYNC_PREREAD          - no operation on intel */
                /* BUS_DMASYNC_POSTWRITE        - no operation on intel */
        }
}

static int
alloc_bounce_zone(bus_dma_tag_t dmat)
{
        struct bounce_zone *bz, *new_bz;

        KASSERT(dmat->bounce_zone == NULL,
                ("bounce zone was already assigned"));

        new_bz = kmalloc(sizeof(*new_bz), M_DEVBUF, M_INTWAIT | M_ZERO);

        lwkt_gettoken(&bounce_zone_tok);

        if ((dmat->flags & BUS_DMA_PRIVBZONE) == 0) {
                /*
                 * For shared bounce zone, check to see
                 * if we already have a suitable zone
                 */
                STAILQ_FOREACH(bz, &bounce_zone_list, links) {
                        if (dmat->alignment <= bz->alignment &&
                            dmat->lowaddr >= bz->lowaddr) {
                                lwkt_reltoken(&bounce_zone_tok);

                                dmat->bounce_zone = bz;
                                kfree(new_bz, M_DEVBUF);
                                return 0;
                        }
                }
        }
        bz = new_bz;

        spin_init(&bz->spin, "allocbouncezone");
        STAILQ_INIT(&bz->bounce_page_list);
        STAILQ_INIT(&bz->bounce_map_waitinglist);
        bz->free_bpages = 0;
        bz->reserved_bpages = 0;
        bz->active_bpages = 0;
        bz->lowaddr = dmat->lowaddr;
        bz->alignment = round_page(dmat->alignment);
        ksnprintf(bz->lowaddrid, 18, "%#jx", (uintmax_t)bz->lowaddr);

        if ((dmat->flags & BUS_DMA_PRIVBZONE) == 0) {
                ksnprintf(bz->zoneid, 8, "zone%d", busdma_zonecount);
                busdma_zonecount++;
                STAILQ_INSERT_TAIL(&bounce_zone_list, bz, links);
        } else {
                ksnprintf(bz->zoneid, 8, "zone%d", busdma_priv_zonecount);
                busdma_priv_zonecount--;
        }

        lwkt_reltoken(&bounce_zone_tok);

        dmat->bounce_zone = bz;

        sysctl_ctx_init(&bz->sysctl_ctx);
        bz->sysctl_tree = SYSCTL_ADD_NODE(&bz->sysctl_ctx,
            SYSCTL_STATIC_CHILDREN(_hw_busdma), OID_AUTO, bz->zoneid,
            CTLFLAG_RD, 0, "");
        if (bz->sysctl_tree == NULL) {
                sysctl_ctx_free(&bz->sysctl_ctx);
                return 0;       /* XXX error code? */
        }

        SYSCTL_ADD_INT(&bz->sysctl_ctx,
            SYSCTL_CHILDREN(bz->sysctl_tree), OID_AUTO,
            "total_bpages", CTLFLAG_RD, &bz->total_bpages, 0,
            "Total bounce pages");
        SYSCTL_ADD_INT(&bz->sysctl_ctx,
            SYSCTL_CHILDREN(bz->sysctl_tree), OID_AUTO,
            "free_bpages", CTLFLAG_RD, &bz->free_bpages, 0,
            "Free bounce pages");
        SYSCTL_ADD_INT(&bz->sysctl_ctx,
            SYSCTL_CHILDREN(bz->sysctl_tree), OID_AUTO,
            "reserved_bpages", CTLFLAG_RD, &bz->reserved_bpages, 0,
            "Reserved bounce pages");
        SYSCTL_ADD_INT(&bz->sysctl_ctx,
            SYSCTL_CHILDREN(bz->sysctl_tree), OID_AUTO,
            "active_bpages", CTLFLAG_RD, &bz->active_bpages, 0,
            "Active bounce pages");
        SYSCTL_ADD_INT(&bz->sysctl_ctx,
            SYSCTL_CHILDREN(bz->sysctl_tree), OID_AUTO,
            "total_bounced", CTLFLAG_RD, &bz->total_bounced, 0,
            "Total bounce requests");
        SYSCTL_ADD_INT(&bz->sysctl_ctx,
            SYSCTL_CHILDREN(bz->sysctl_tree), OID_AUTO,
            "total_deferred", CTLFLAG_RD, &bz->total_deferred, 0,
            "Total bounce requests that were deferred");
        SYSCTL_ADD_INT(&bz->sysctl_ctx,
            SYSCTL_CHILDREN(bz->sysctl_tree), OID_AUTO,
            "reserve_failed", CTLFLAG_RD, &bz->reserve_failed, 0,
            "Total bounce page reservations that were failed");
        SYSCTL_ADD_STRING(&bz->sysctl_ctx,
            SYSCTL_CHILDREN(bz->sysctl_tree), OID_AUTO,
            "lowaddr", CTLFLAG_RD, bz->lowaddrid, 0, "");
        SYSCTL_ADD_INT(&bz->sysctl_ctx,
            SYSCTL_CHILDREN(bz->sysctl_tree), OID_AUTO,
            "alignment", CTLFLAG_RD, &bz->alignment, 0, "");

        return 0;
}

static int
alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages, int flags)
{
        struct bounce_zone *bz = dmat->bounce_zone;
        int count = 0, mflags;

        if (flags & BUS_DMA_NOWAIT)
                mflags = M_NOWAIT;
        else
                mflags = M_WAITOK;

        while (numpages > 0) {
                struct bounce_page *bpage;

                bpage = kmalloc(sizeof(*bpage), M_DEVBUF, M_INTWAIT | M_ZERO);

                bpage->vaddr = (vm_offset_t)contigmalloc(PAGE_SIZE, M_DEVBUF,
                                                         mflags, 0ul,
                                                         bz->lowaddr,
                                                         bz->alignment, 0);
                if (bpage->vaddr == 0) {
                        kfree(bpage, M_DEVBUF);
                        break;
                }
                bpage->busaddr = pmap_kextract(bpage->vaddr);

                BZ_LOCK(bz);
                STAILQ_INSERT_TAIL(&bz->bounce_page_list, bpage, links);
                total_bounce_pages++;
                bz->total_bpages++;
                bz->free_bpages++;
                BZ_UNLOCK(bz);

                count++;
                numpages--;
        }
        return count;
}

static void
free_bounce_pages_all(bus_dma_tag_t dmat)
{
        struct bounce_zone *bz = dmat->bounce_zone;
        struct bounce_page *bpage;

        BZ_LOCK(bz);

        while ((bpage = STAILQ_FIRST(&bz->bounce_page_list)) != NULL) {
                STAILQ_REMOVE_HEAD(&bz->bounce_page_list, links);

                KKASSERT(total_bounce_pages > 0);
                total_bounce_pages--;

                KKASSERT(bz->total_bpages > 0);
                bz->total_bpages--;

                KKASSERT(bz->free_bpages > 0);
                bz->free_bpages--;

                BZ_UNLOCK(bz);
                contigfree((void *)bpage->vaddr, PAGE_SIZE, M_DEVBUF);
                kfree(bpage, M_DEVBUF);
                BZ_LOCK(bz);
        }
        if (bz->total_bpages) {
                kprintf("#%d bounce pages are still in use\n",
                        bz->total_bpages);
                print_backtrace(-1);
        }

        BZ_UNLOCK(bz);
}

static void
free_bounce_zone(bus_dma_tag_t dmat)
{
        struct bounce_zone *bz = dmat->bounce_zone;

        if (bz == NULL)
                return;

        if ((dmat->flags & BUS_DMA_PRIVBZONE) == 0)
                return;

        free_bounce_pages_all(dmat);
        dmat->bounce_zone = NULL;

        if (bz->sysctl_tree != NULL)
                sysctl_ctx_free(&bz->sysctl_ctx);
        kfree(bz, M_DEVBUF);
}

/* Assume caller holds bounce zone spinlock */
static int
reserve_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map, int commit)
{
        struct bounce_zone *bz = dmat->bounce_zone;
        int pages;

        pages = MIN(bz->free_bpages, map->pagesneeded - map->pagesreserved);
        if (!commit && map->pagesneeded > (map->pagesreserved + pages)) {
                bz->reserve_failed++;
                return (map->pagesneeded - (map->pagesreserved + pages));
        }

        bz->free_bpages -= pages;

        bz->reserved_bpages += pages;
        KKASSERT(bz->reserved_bpages <= bz->total_bpages);

        map->pagesreserved += pages;
        pages = map->pagesneeded - map->pagesreserved;

        return pages;
}

static void
return_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map)
{
        struct bounce_zone *bz = dmat->bounce_zone;
        int reserved = map->pagesreserved;
        bus_dmamap_t wait_map;

        map->pagesreserved = 0;
        map->pagesneeded = 0;

        if (reserved == 0)
                return;

        BZ_LOCK(bz);

        bz->free_bpages += reserved;
        KKASSERT(bz->free_bpages <= bz->total_bpages);

        KKASSERT(bz->reserved_bpages >= reserved);
        bz->reserved_bpages -= reserved;

        wait_map = get_map_waiting(dmat);

        BZ_UNLOCK(bz);

        if (wait_map != NULL)
                add_map_callback(map);
}

static bus_addr_t
add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map, vm_offset_t vaddr,
                bus_size_t *sizep)
{
        struct bounce_zone *bz = dmat->bounce_zone;
        struct bounce_page *bpage;
        bus_size_t size;

        KASSERT(map->pagesneeded > 0, ("map doesn't need any pages"));
        map->pagesneeded--;

        KASSERT(map->pagesreserved > 0, ("map doesn't reserve any pages"));
        map->pagesreserved--;

        BZ_LOCK(bz);

        bpage = STAILQ_FIRST(&bz->bounce_page_list);
        KASSERT(bpage != NULL, ("free page list is empty"));
        STAILQ_REMOVE_HEAD(&bz->bounce_page_list, links);

        KKASSERT(bz->reserved_bpages > 0);
        bz->reserved_bpages--;

        bz->active_bpages++;
        KKASSERT(bz->active_bpages <= bz->total_bpages);

        BZ_UNLOCK(bz);

        if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
                /*
                 * Page offset needs to be preserved.  No size adjustments
                 * needed.
                 */
                bpage->vaddr |= vaddr & PAGE_MASK;
                bpage->busaddr |= vaddr & PAGE_MASK;
                size = *sizep;
        } else {
                /*
                 * Realign to bounce page base address, reduce size if
                 * necessary.  Bounce pages are typically already
                 * page-aligned.
                 */
                size = PAGE_SIZE - (bpage->busaddr & PAGE_MASK);
                if (size < *sizep) {
                        *sizep = size;
                } else {
                        size = *sizep;
                }
        }

        bpage->datavaddr = vaddr;
        bpage->datacount = size;
        STAILQ_INSERT_TAIL(&map->bpages, bpage, links);
        return bpage->busaddr;
}

static void
free_bounce_page(bus_dma_tag_t dmat, struct bounce_page *bpage)
{
        struct bounce_zone *bz = dmat->bounce_zone;
        bus_dmamap_t map;

        bpage->datavaddr = 0;
        bpage->datacount = 0;
 
        if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
                /*
                 * Reset the bounce page to start at offset 0.  Other uses
                 * of this bounce page may need to store a full page of
                 * data and/or assume it starts on a page boundary.
                 */
                bpage->vaddr &= ~PAGE_MASK;
                bpage->busaddr &= ~PAGE_MASK;
        }

        BZ_LOCK(bz);

        STAILQ_INSERT_HEAD(&bz->bounce_page_list, bpage, links);

        bz->free_bpages++;
        KKASSERT(bz->free_bpages <= bz->total_bpages);

        KKASSERT(bz->active_bpages > 0);
        bz->active_bpages--;

        map = get_map_waiting(dmat);

        BZ_UNLOCK(bz);

        if (map != NULL)
                add_map_callback(map);
}

/* Assume caller holds bounce zone spinlock */
static bus_dmamap_t
get_map_waiting(bus_dma_tag_t dmat)
{
        struct bounce_zone *bz = dmat->bounce_zone;
        bus_dmamap_t map;

        map = STAILQ_FIRST(&bz->bounce_map_waitinglist);
        if (map != NULL) {
                if (reserve_bounce_pages(map->dmat, map, 1) == 0) {
                        STAILQ_REMOVE_HEAD(&bz->bounce_map_waitinglist, links);
                        bz->total_deferred++;
                } else {
                        map = NULL;
                }
        }
        return map;
}

static void
add_map_callback(bus_dmamap_t map)
{
        spin_lock(&bounce_map_list_spin);
        STAILQ_INSERT_TAIL(&bounce_map_callbacklist, map, links);
        busdma_swi_pending = 1;
        setsoftvm();
        spin_unlock(&bounce_map_list_spin);
}

void
busdma_swi(void)
{
        bus_dmamap_t map;

        spin_lock(&bounce_map_list_spin);
        while ((map = STAILQ_FIRST(&bounce_map_callbacklist)) != NULL) {
                STAILQ_REMOVE_HEAD(&bounce_map_callbacklist, links);
                spin_unlock(&bounce_map_list_spin);
                bus_dmamap_load(map->dmat, map, map->buf, map->buflen,
                                map->callback, map->callback_arg, /*flags*/0);
                spin_lock(&bounce_map_list_spin);
        }
        spin_unlock(&bounce_map_list_spin);
}