Implement boundary and maximum segment size handling in bus_dmamap_load().

[dragonfly/vkernel-mp.git] / sys / platform / pc32 / i386 / 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 1.16.2.2 2003/01/23 00:55:27 scottl Exp $
 * $DragonFly: src/sys/platform/pc32/i386/busdma_machdep.c,v 1.19 2007/06/03 11:47:10 dillon Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/uio.h>
#include <sys/thread2.h>
#include <sys/bus_dma.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 <sys/lock.h>
#include <vm/vm_map.h>

#include <machine/md_var.h>

#define MAX_BPAGES 128

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_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;
};

int busdma_swi_pending;

static STAILQ_HEAD(bp_list, bounce_page) bounce_page_list;
static int free_bpages;
static int reserved_bpages;
static int active_bpages;
static int total_bpages;
static bus_addr_t bounce_lowaddr = BUS_SPACE_MAXADDR;

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_waitinglist;
static STAILQ_HEAD(, bus_dmamap) bounce_map_callbacklist;
static struct bus_dmamap nobounce_dmamap;

static int alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages);
static int reserve_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map);
static bus_addr_t add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map,
                                   vm_offset_t vaddr, bus_size_t size);
static void free_bounce_page(bus_dma_tag_t dmat, struct bounce_page *bpage);
static __inline int run_filter(bus_dma_tag_t dmat, bus_addr_t paddr);

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
                 && (dmat->filter == NULL
                  || (*dmat->filter)(dmat->filterarg, paddr) != 0))
                        retval = 1;

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

#define BUS_DMA_MIN_ALLOC_COMP BUS_DMA_BUS4
/*
 * 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;

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

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

        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;
        
        /* 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);
                /*
                 * XXX Not really correct??? Probably need to honor boundary
                 *     all the way up the inheritence chain.
                 */
                newtag->boundary = MAX(parent->boundary, newtag->boundary);
                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) &&
            (flags & BUS_DMA_ALLOCNOW) != 0) {
                /* Must bounce */

                if (lowaddr > bounce_lowaddr) {
                        /*
                         * Go through the pool and kill any pages
                         * that don't reside below lowaddr.
                         */
                        panic("bus_dma_tag_create: page reallocation "
                              "not implemented");
                }
                if (ptoa(total_bpages) < maxsize) {
                        int pages;

                        pages = atop(maxsize) - total_bpages;

                        /* Add pages to our bounce pool */
                        if (alloc_bounce_pages(newtag, pages) < pages)
                                error = ENOMEM;
                }
                /* Performed initial allocation */
                newtag->flags |= BUS_DMA_MIN_ALLOC_COMP;
        }
        
        if (error != 0) {
                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) {
                                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);
}

/*
 * 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->lowaddr < ptoa(Maxmem)) {
                /* Must bounce */
                int maxpages;

                *mapp = kmalloc(sizeof(**mapp), M_DEVBUF, M_INTWAIT);
                if (*mapp == NULL) {
                        return (ENOMEM);
                } else {
                        /* Initialize the new map */
                        bzero(*mapp, sizeof(**mapp));
                        STAILQ_INIT(&((*mapp)->bpages));
                }
                /*
                 * Attempt to add pages to our pool on a per-instance
                 * basis up to a sane limit.
                 */
                maxpages = MIN(MAX_BPAGES, Maxmem - atop(dmat->lowaddr));
                if ((dmat->flags & BUS_DMA_MIN_ALLOC_COMP) == 0
                 || (dmat->map_count > 0
                  && total_bpages < maxpages)) {
                        int pages;

                        if (dmat->lowaddr > bounce_lowaddr) {
                                /*
                                 * Go through the pool and kill any pages
                                 * that don't reside below lowaddr.
                                 */
                                panic("bus_dmamap_create: page reallocation "
                                      "not implemented");
                        }
                        pages = atop(dmat->maxsize);
                        pages = MIN(maxpages - total_bpages, pages);
                        error = alloc_bounce_pages(dmat, pages);

                        if ((dmat->flags & BUS_DMA_MIN_ALLOC_COMP) == 0) {
                                if (error == 0)
                                        dmat->flags |= BUS_DMA_MIN_ALLOC_COMP;
                        } else {
                                error = 0;
                        }
                }
        } else {
                *mapp = NULL;
        }
        if (error == 0)
                dmat->map_count++;
        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);
}


/*
 * 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)
{
        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 ((dmat->maxsize <= PAGE_SIZE) &&
            dmat->lowaddr >= ptoa(Maxmem)) {
                *vaddr = kmalloc(dmat->maxsize, M_DEVBUF, mflags);
                /*
                 * XXX Check whether the allocation crossed a page boundary
                 * and retry with power-of-2 alignment in that case.
                 */
                if ((((intptr_t)*vaddr) & PAGE_MASK) !=
                    (((intptr_t)*vaddr + dmat->maxsize) & PAGE_MASK)) {
                        size_t size;
                        kfree(*vaddr, M_DEVBUF);
                        /* XXX check for overflow? */
                        for (size = 1; size <= dmat->maxsize; size <<= 1)
                                ;
                        *vaddr = kmalloc(size, M_DEVBUF, mflags);
                }
        } 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->alignment : 1ul,
                    dmat->boundary);
        }
        if (*vaddr == NULL)
                return (ENOMEM);
        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\n");
        if ((dmat->maxsize <= PAGE_SIZE) &&
            dmat->lowaddr >= ptoa(Maxmem))
                kfree(vaddr, M_DEVBUF);
        else
                contigfree(vaddr, dmat->maxsize, M_DEVBUF);
}

#define BUS_DMAMAP_NSEGS ((BUS_SPACE_MAXSIZE / PAGE_SIZE) + 1)

/*
 * 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)
{
        vm_offset_t             vaddr;
        vm_paddr_t              paddr;
        bus_dma_segment_t      *sg;
        int                     seg;
        int                     error;
        vm_paddr_t              nextpaddr;
        bus_addr_t              bmask;

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

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

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

                while (vaddr < vendaddr) {
                        paddr = pmap_kextract(vaddr);
                        if (run_filter(dmat, paddr) != 0) {

                                map->pagesneeded++;
                        }
                        vaddr += PAGE_SIZE;
                }
        }

        /* Reserve Necessary Bounce Pages */
        if (map->pagesneeded != 0) {
                crit_enter();
                if (reserve_bounce_pages(dmat, map) != 0) {

                        /* Queue us for resources */
                        map->dmat = dmat;
                        map->buf = buf;
                        map->buflen = buflen;
                        map->callback = callback;
                        map->callback_arg = callback_arg;

                        STAILQ_INSERT_TAIL(&bounce_map_waitinglist, map, links);
                        crit_exit();

                        return (EINPROGRESS);
                }
                crit_exit();
        }

        vaddr = (vm_offset_t)buf;
        sg = dmat->segments;
        seg = 1;
        sg->ds_len = 0;
        nextpaddr = 0;
        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 = pmap_kextract(vaddr);
                size = PAGE_SIZE - (paddr & PAGE_MASK);
                if (size > buflen)
                        size = buflen;
                if (map->pagesneeded != 0 && run_filter(dmat, paddr)) {
                        /* 
                         * note: this paddr has the same in-page offset
                         * as vaddr and thus the paddr above, so the
                         * size does not have to be recalculated
                         */
                        paddr = add_bounce_page(dmat, map, vaddr, size);
                }

                /*
                 * Fill in the bus_dma_segment
                 */
                if (sg->ds_len == 0) {
                        sg->ds_addr = paddr;
                        sg->ds_len = size;
                } else if (paddr == nextpaddr) {
                        sg->ds_len += size;
                } else {
                        sg++;
                        seg++;
                        if (seg > dmat->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 ^ 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 >= dmat->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) {
                kprintf("bus_dmamap_load: Too many segs! buf_len = 0x%lx\n",
                       (u_long)buflen);
                error = EFBIG;
        }

        (*callback)(callback_arg, dmat->segments, seg, error);

        return (0);
}

/*
 * Utility function to load a linear buffer.  lastaddrp holds state
 * between invocations (for multiple-buffer loads).  segp contains
 * the starting segment 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,
                        void *buf, bus_size_t buflen,
                        struct thread *td,
                        int flags,
                        vm_offset_t *lastaddrp,
                        int *segp,
                        int first)
{
        bus_dma_segment_t *segs;
        bus_size_t sgsize;
        bus_addr_t curaddr, lastaddr, baddr, bmask;
        vm_offset_t vaddr = (vm_offset_t)buf;
        int seg;
        pmap_t pmap;

        if (td->td_proc != NULL)
                pmap = vmspace_pmap(td->td_proc->p_vmspace);
        else
                pmap = NULL;

        segs = dmat->segments;
        lastaddr = *lastaddrp;
        bmask  = ~(dmat->boundary - 1);

        for (seg = *segp; buflen > 0 ; ) {
                /*
                 * Get the physical address for this segment.
                 */
                if (pmap)
                        curaddr = pmap_extract(pmap, vaddr);
                else
                        curaddr = pmap_kextract(vaddr);

                /*
                 * Compute the segment size, and adjust counts.
                 */
                sgsize = PAGE_SIZE - ((u_long)curaddr & PAGE_MASK);
                if (buflen < sgsize)
                        sgsize = buflen;

                /*
                 * Make sure we don't cross any boundaries.
                 */
                if (dmat->boundary > 0) {
                        baddr = (curaddr + dmat->boundary) & bmask;
                        if (sgsize > (baddr - curaddr))
                                sgsize = (baddr - curaddr);
                }

                /*
                 * Insert chunk into a segment, coalescing with
                 * previous segment if possible.
                 */
                if (first) {
                        segs[seg].ds_addr = curaddr;
                        segs[seg].ds_len = sgsize;
                        first = 0;
                } else {
                        if (curaddr == lastaddr &&
                            (segs[seg].ds_len + sgsize) <= dmat->maxsegsz &&
                            (dmat->boundary == 0 ||
                             (segs[seg].ds_addr & bmask) == (curaddr & bmask)))
                                segs[seg].ds_len += sgsize;
                        else {
                                if (++seg >= dmat->nsegments)
                                        break;
                                segs[seg].ds_addr = curaddr;
                                segs[seg].ds_len = sgsize;
                        }
                }

                lastaddr = curaddr + sgsize;
                vaddr += sgsize;
                buflen -= sgsize;
        }

        *segp = seg;
        *lastaddrp = lastaddr;

        /*
         * Did we fit?
         */
        return (buflen != 0 ? EFBIG : 0); /* XXX better return value here? */
}

/*
 * 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)
{
        int nsegs, error;

        KASSERT(dmat->lowaddr >= ptoa(Maxmem) || map != NULL,
                ("bus_dmamap_load_mbuf: No support for bounce pages!"));
        KASSERT(m0->m_flags & M_PKTHDR,
                ("bus_dmamap_load_mbuf: no packet header"));

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

                for (m = m0; m != NULL && error == 0; m = m->m_next) {
                        if ( m->m_len == 0 )
                                continue;
                        error = _bus_dmamap_load_buffer(dmat,
                                        m->m_data, m->m_len,
                                        curthread, flags, &lastaddr,
                                        &nsegs, first);
                        first = 0;
                }
        } else {
                error = EINVAL;
        }

        if (error) {
                /* force "no valid mappings" in callback */
                (*callback)(callback_arg, dmat->segments, 0, 0, error);
        } else {
                (*callback)(callback_arg, dmat->segments,
                            nsegs+1, m0->m_pkthdr.len, error);
        }
        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_offset_t lastaddr;
        int nsegs, error, first, i;
        bus_size_t resid;
        struct iovec *iov;
        struct thread *td = NULL;

        KASSERT(dmat->lowaddr >= ptoa(Maxmem) || map != NULL,
                ("bus_dmamap_load_uio: No support for bounce pages!"));

        resid = uio->uio_resid;
        iov = uio->uio_iov;

        if (uio->uio_segflg == UIO_USERSPACE) {
                td = uio->uio_td;
                KASSERT(td != NULL && td->td_proc != NULL,
                        ("bus_dmamap_load_uio: USERSPACE but no proc"));
        }

        nsegs = 0;
        error = 0;
        first = 1;
        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,
                                addr, minlen,
                                td, flags, &lastaddr, &nsegs, first);
                first = 0;

                resid -= minlen;
        }

        if (error) {
                /* force "no valid mappings" in callback */
                (*callback)(callback_arg, dmat->segments, 0, 0, error);
        } else {
                (*callback)(callback_arg, dmat->segments,
                            nsegs+1, uio->uio_resid, error);
        }
        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
                 */
                switch (op) {
                case BUS_DMASYNC_PREWRITE:
                        while (bpage != NULL) {
                                bcopy((void *)bpage->datavaddr,
                                      (void *)bpage->vaddr,
                                      bpage->datacount);
                                bpage = STAILQ_NEXT(bpage, links);
                        }
                        break;

                case BUS_DMASYNC_POSTREAD:
                        while (bpage != NULL) {
                                bcopy((void *)bpage->vaddr,
                                      (void *)bpage->datavaddr,
                                      bpage->datacount);
                                bpage = STAILQ_NEXT(bpage, links);
                        }
                        break;
                case BUS_DMASYNC_PREREAD:
                case BUS_DMASYNC_POSTWRITE:
                        /* No-ops */
                        break;
                }
        }
}

static int
alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages)
{
        int count;

        count = 0;
        if (total_bpages == 0) {
                STAILQ_INIT(&bounce_page_list);
                STAILQ_INIT(&bounce_map_waitinglist);
                STAILQ_INIT(&bounce_map_callbacklist);
        }
        
        while (numpages > 0) {
                struct bounce_page *bpage;

                bpage = (struct bounce_page *)kmalloc(sizeof(*bpage), M_DEVBUF,
                                                     M_INTWAIT);

                if (bpage == NULL)
                        break;
                bzero(bpage, sizeof(*bpage));
                bpage->vaddr = (vm_offset_t)contigmalloc(PAGE_SIZE, M_DEVBUF,
                                                         M_NOWAIT, 0ul,
                                                         dmat->lowaddr,
                                                         PAGE_SIZE,
                                                         0);
                if (bpage->vaddr == NULL) {
                        kfree(bpage, M_DEVBUF);
                        break;
                }
                bpage->busaddr = pmap_kextract(bpage->vaddr);
                crit_enter();
                STAILQ_INSERT_TAIL(&bounce_page_list, bpage, links);
                total_bpages++;
                free_bpages++;
                crit_exit();
                count++;
                numpages--;
        }
        return (count);
}

static int
reserve_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map)
{
        int pages;

        pages = MIN(free_bpages, map->pagesneeded - map->pagesreserved);
        free_bpages -= pages;
        reserved_bpages += pages;
        map->pagesreserved += pages;
        pages = map->pagesneeded - map->pagesreserved;

        return (pages);
}

static bus_addr_t
add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map, vm_offset_t vaddr,
                bus_size_t size)
{
        struct bounce_page *bpage;

        if (map->pagesneeded == 0)
                panic("add_bounce_page: map doesn't need any pages");
        map->pagesneeded--;

        if (map->pagesreserved == 0)
                panic("add_bounce_page: map doesn't need any pages");
        map->pagesreserved--;

        crit_enter();
        bpage = STAILQ_FIRST(&bounce_page_list);
        if (bpage == NULL)
                panic("add_bounce_page: free page list is empty");

        STAILQ_REMOVE_HEAD(&bounce_page_list, links);
        reserved_bpages--;
        active_bpages++;
        crit_exit();

        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 bus_dmamap *map;

        bpage->datavaddr = 0;
        bpage->datacount = 0;

        crit_enter();
        STAILQ_INSERT_HEAD(&bounce_page_list, bpage, links);
        free_bpages++;
        active_bpages--;
        if ((map = STAILQ_FIRST(&bounce_map_waitinglist)) != NULL) {
                if (reserve_bounce_pages(map->dmat, map) == 0) {
                        STAILQ_REMOVE_HEAD(&bounce_map_waitinglist, links);
                        STAILQ_INSERT_TAIL(&bounce_map_callbacklist,
                                           map, links);
                        busdma_swi_pending = 1;
                        setsoftvm();
                }
        }
        crit_exit();
}

void
busdma_swi(void)
{
        struct bus_dmamap *map;

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