/*      $OpenBSD: bus_dma.c,v 1.17 2019/12/20 13:34:41 visa Exp $ */

/*
 * Copyright (c) 2003-2004 Opsycon AB  (www.opsycon.se / www.opsycon.com)
 *
 * 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.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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.
 *
 */
/*-
 * Copyright (c) 1996, 1997, 1998 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
 * NASA Ames Research Center.
 *
 * 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.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>

#include <uvm/uvm_extern.h>

#include <mips64/cache.h>
#include <machine/cpu.h>
#include <machine/autoconf.h>

#include <machine/bus.h>

/*
 * Common function for DMA map creation.  May be called by bus-specific
 * DMA map creation functions.
 */
int
_dmamap_create(bus_dma_tag_t t, bus_size_t size, int nsegments,
    bus_size_t maxsegsz, bus_size_t boundary, int flags, bus_dmamap_t *dmamp)
{
        struct machine_bus_dmamap *map;
        void *mapstore;
        size_t mapsize;

        /*
         * Allocate and initialize the DMA map.  The end of the map
         * is a variable-sized array of segments, so we allocate enough
         * room for them in one shot.
         *
         * Note we don't preserve the WAITOK or NOWAIT flags.  Preservation
         * of ALLOCNOW notifies others that we've reserved these resources,
         * and they are not to be freed.
         *
         * The bus_dmamap_t includes one bus_dma_segment_t, hence
         * the (nsegments - 1).
         */
        mapsize = sizeof(struct machine_bus_dmamap) +
            (sizeof(bus_dma_segment_t) * (nsegments - 1));
        if ((mapstore = malloc(mapsize, M_DEVBUF, (flags & BUS_DMA_NOWAIT) ?
            (M_NOWAIT | M_ZERO) : (M_WAITOK | M_ZERO))) == NULL)
                return (ENOMEM);

        map = (struct machine_bus_dmamap *)mapstore;
        map->_dm_size = size;
        map->_dm_segcnt = nsegments;
        map->_dm_maxsegsz = maxsegsz;
        map->_dm_boundary = boundary;
        map->_dm_flags = flags & ~(BUS_DMA_WAITOK|BUS_DMA_NOWAIT);

        *dmamp = map;
        return (0);
}

/*
 * Common function for DMA map destruction.  May be called by bus-specific
 * DMA map destruction functions.
 */
void
_dmamap_destroy(bus_dma_tag_t t, bus_dmamap_t map)
{
        size_t mapsize;

        mapsize = sizeof(struct machine_bus_dmamap) +
            (sizeof(bus_dma_segment_t) * (map->_dm_segcnt - 1));
        free(map, M_DEVBUF, mapsize);
}

/*
 * Common function for loading a DMA map with a linear buffer.  May
 * be called by bus-specific DMA map load functions.
 */
int
_dmamap_load(bus_dma_tag_t t, bus_dmamap_t map, void *buf, bus_size_t buflen,
    struct proc *p, int flags)
{
        paddr_t lastaddr;
        int seg, error;

        /*
         * Make sure that on error condition we return "no valid mappings".
         */
        map->dm_nsegs = 0;
        map->dm_mapsize = 0;

        if (buflen > map->_dm_size)
                return (EINVAL);

        seg = 0;
        error = (*t->_dmamap_load_buffer)(t, map, buf, buflen, p, flags,
            &lastaddr, &seg, 1);
        if (error == 0) {
                map->dm_nsegs = seg + 1;
                map->dm_mapsize = buflen;
        }

        return (error);
}

/*
 * Like _bus_dmamap_load(), but for mbufs.
 */
int
_dmamap_load_mbuf(bus_dma_tag_t t, bus_dmamap_t map, struct mbuf *m0, int flags)
{
        paddr_t lastaddr;
        int seg, error, first;
        struct mbuf *m;

        /*
         * Make sure that on error condition we return "no valid mappings".
         */
        map->dm_nsegs = 0;
        map->dm_mapsize = 0;

#ifdef DIAGNOSTIC
        if ((m0->m_flags & M_PKTHDR) == 0)
                panic("_dmamap_load_mbuf: no packet header");
#endif

        if (m0->m_pkthdr.len > map->_dm_size)
                return (EINVAL);

        first = 1;
        seg = 0;
        error = 0;
        for (m = m0; m != NULL && error == 0; m = m->m_next) {
                if (m->m_len == 0)
                        continue;
                error = (*t->_dmamap_load_buffer)(t, map, m->m_data, m->m_len,
                    NULL, flags, &lastaddr, &seg, first);
                first = 0;
        }
        if (error == 0) {
                map->dm_nsegs = seg + 1;
                map->dm_mapsize = m0->m_pkthdr.len;
        }

        return (error);
}

/*
 * Like _dmamap_load(), but for uios.
 */
int
_dmamap_load_uio(bus_dma_tag_t t, bus_dmamap_t map, struct uio *uio, int flags)
{
        paddr_t lastaddr;
        int seg, i, error, first;
        bus_size_t minlen, resid;
        struct proc *p = NULL;
        struct iovec *iov;
        void *addr;

        /*
         * Make sure that on error condition we return "no valid mappings".
         */
        map->dm_nsegs = 0;
        map->dm_mapsize = 0;

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

        if (uio->uio_segflg == UIO_USERSPACE) {
                p = uio->uio_procp;
#ifdef DIAGNOSTIC
                if (p == NULL)
                        panic("_dmamap_load_uio: USERSPACE but no proc");
#endif
        }

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

                error = (*t->_dmamap_load_buffer)(t, map, addr, minlen,
                    p, flags, &lastaddr, &seg, first);
                first = 0;

                resid -= minlen;
        }
        if (error == 0) {
                map->dm_nsegs = seg + 1;
                map->dm_mapsize = uio->uio_resid;
        }

        return (error);
}

/*
 * Like _dmamap_load(), but for raw memory allocated with
 * bus_dmamem_alloc().
 */
int
_dmamap_load_raw(bus_dma_tag_t t, bus_dmamap_t map, bus_dma_segment_t *segs,
    int nsegs, bus_size_t size, int flags)
{
        bus_addr_t paddr, baddr, bmask, lastaddr = 0;
        bus_size_t plen, sgsize, mapsize;
        int first = 1;
        int i, seg = 0;

        /*
         * Make sure that on error condition we return "no valid mappings".
         */
        map->dm_mapsize = 0;
        map->dm_nsegs = 0;

        if (nsegs > map->_dm_segcnt || size > map->_dm_size)
                return (EINVAL);

        mapsize = size;
        bmask = ~(map->_dm_boundary - 1);

        for (i = 0; i < nsegs && size > 0; i++) {
                paddr = segs[i].ds_addr;
                plen = MIN(segs[i].ds_len, size);

                while (plen > 0) {
                        /*
                         * Compute the segment size, and adjust counts.
                         */
                        sgsize = PAGE_SIZE - ((u_long)paddr & PGOFSET);
                        if (plen < sgsize)
                                sgsize = plen;

                        if (paddr > dma_constraint.ucr_high)
                                panic("Non dma-reachable buffer at "
                                    "paddr %#lx(raw)", paddr);

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

                        /*
                         * Insert chunk into a segment, coalescing with
                         * previous segment if possible.
                         */
                        if (first) {
                                map->dm_segs[seg].ds_addr = paddr;
                                map->dm_segs[seg].ds_len = sgsize;
                                first = 0;
                        } else {
                                if (paddr == lastaddr &&
                                    (map->dm_segs[seg].ds_len + sgsize) <=
                                     map->_dm_maxsegsz &&
                                    (map->_dm_boundary == 0 ||
                                     (map->dm_segs[seg].ds_addr & bmask) ==
                                     (paddr & bmask)))
                                        map->dm_segs[seg].ds_len += sgsize;
                                else {
                                        if (++seg >= map->_dm_segcnt)
                                                return (EINVAL);
                                        map->dm_segs[seg].ds_addr = paddr;
                                        map->dm_segs[seg].ds_len = sgsize;
                                }
                        }

                        paddr += sgsize;
                        plen -= sgsize;
                        size -= sgsize;

                        lastaddr = paddr;
                }
        }

        map->dm_mapsize = mapsize;
        map->dm_nsegs = seg + 1;
        return (0);
}

/*
 * Common function for unloading a DMA map.  May be called by
 * bus-specific DMA map unload functions.
 */
void
_dmamap_unload(bus_dma_tag_t t, bus_dmamap_t map)
{
        /*
         * No resources to free; just mark the mappings as
         * invalid.
         */
        map->dm_nsegs = 0;
        map->dm_mapsize = 0;
}

/*
 * Common function for DMA map synchronization.  May be called
 * by bus-specific DMA map synchronization functions.
 */
void
_dmamap_sync(bus_dma_tag_t t, bus_dmamap_t map, bus_addr_t addr,
    bus_size_t size, int op)
{
        int nsegs;
        int curseg;
        struct cpu_info *ci = curcpu();

        nsegs = map->dm_nsegs;
        curseg = 0;

        while (size && nsegs) {
                paddr_t paddr;
                vaddr_t vaddr;
                bus_size_t ssize;

                ssize = map->dm_segs[curseg].ds_len;
                paddr = map->dm_segs[curseg]._ds_paddr;
                vaddr = map->dm_segs[curseg]._ds_vaddr;

                if (addr != 0) {
                        if (addr >= ssize) {
                                addr -= ssize;
                                ssize = 0;
                        } else {
                                vaddr += addr;
                                paddr += addr;
                                ssize -= addr;
                                addr = 0;
                        }
                }
                if (ssize > size)
                        ssize = size;

                if (IS_XKPHYS(vaddr) && XKPHYS_TO_CCA(vaddr) == CCA_NC) {
                        size -= ssize;
                        ssize = 0;
                }

                if (ssize != 0) {
                        /*
                         * If only PREWRITE is requested, writeback.
                         * PREWRITE with PREREAD writebacks
                         * and invalidates (if noncoherent) *all* cache levels.
                         * Otherwise, just invalidate (if noncoherent).
                         */
                        if (op & BUS_DMASYNC_PREWRITE) {
                                if (op & BUS_DMASYNC_PREREAD)
                                        Mips_IOSyncDCache(ci, vaddr,
                                            ssize, CACHE_SYNC_X);
                                else
                                        Mips_IOSyncDCache(ci, vaddr,
                                            ssize, CACHE_SYNC_W);
                        } else
                        if (op & (BUS_DMASYNC_PREREAD | BUS_DMASYNC_POSTREAD)) {
                                Mips_IOSyncDCache(ci, vaddr,
                                    ssize, CACHE_SYNC_R);
                        }
                        size -= ssize;
                }
                curseg++;
                nsegs--;
        }

        if (size != 0) {
                panic("_dmamap_sync: ran off map!");
        }
}

/*
 * Common function for DMA-safe memory allocation.  May be called
 * by bus-specific DMA memory allocation functions.
 */
int
_dmamem_alloc(bus_dma_tag_t t, bus_size_t size, bus_size_t alignment,
    bus_size_t boundary, bus_dma_segment_t *segs, int nsegs, int *rsegs,
    int flags)
{
        return _dmamem_alloc_range(t, size, alignment, boundary,
            segs, nsegs, rsegs, flags, (paddr_t)0, (paddr_t)-1);
}

/*
 * Common function for freeing DMA-safe memory.  May be called by
 * bus-specific DMA memory free functions.
 */
void
_dmamem_free(bus_dma_tag_t t, bus_dma_segment_t *segs, int nsegs)
{
        vm_page_t m;
        bus_addr_t addr;
        struct pglist mlist;
        int curseg;

        /*
         * Build a list of pages to free back to the VM system.
         */
        TAILQ_INIT(&mlist);
        for (curseg = 0; curseg < nsegs; curseg++) {
                for (addr = segs[curseg].ds_addr;
                    addr < (segs[curseg].ds_addr + segs[curseg].ds_len);
                    addr += PAGE_SIZE) {
                        m = PHYS_TO_VM_PAGE((*t->_device_to_pa)(addr));
                        TAILQ_INSERT_TAIL(&mlist, m, pageq);
                }
        }

        uvm_pglistfree(&mlist);
}

/*
 * Common function for mapping DMA-safe memory.  May be called by
 * bus-specific DMA memory map functions.
 */
int
_dmamem_map(bus_dma_tag_t t, bus_dma_segment_t *segs, int nsegs, size_t size,
    caddr_t *kvap, int flags)
{
        vaddr_t va, sva;
        size_t ssize;
        paddr_t pa;
        bus_addr_t addr;
        int curseg, error, pmap_flags;
        const struct kmem_dyn_mode *kd;

        if (nsegs == 1) {
                pa = (*t->_device_to_pa)(segs[0].ds_addr);
                if (flags & (BUS_DMA_COHERENT | BUS_DMA_NOCACHE))
                        *kvap = (caddr_t)PHYS_TO_XKPHYS(pa, CCA_NC);
                else
                        *kvap = (caddr_t)PHYS_TO_XKPHYS(pa, CCA_CACHED);
                return (0);
        }

        size = round_page(size);
        kd = flags & BUS_DMA_NOWAIT ? &kd_trylock : &kd_waitok;
        va = (vaddr_t)km_alloc(size, &kv_any, &kp_none, kd);
        if (va == 0)
                return (ENOMEM);

        *kvap = (caddr_t)va;

        sva = va;
        ssize = size;
        pmap_flags = PMAP_WIRED | PMAP_CANFAIL;
        if (flags & (BUS_DMA_COHERENT | BUS_DMA_NOCACHE))
                pmap_flags |= PMAP_NOCACHE;
        for (curseg = 0; curseg < nsegs; curseg++) {
                for (addr = segs[curseg].ds_addr;
                    addr < (segs[curseg].ds_addr + segs[curseg].ds_len);
                    addr += NBPG, va += NBPG, size -= NBPG) {
                        if (size == 0)
                                panic("_dmamem_map: size botch");
                        pa = (*t->_device_to_pa)(addr);
                        error = pmap_enter(pmap_kernel(), va, pa,
                            PROT_READ | PROT_WRITE,
                            PROT_READ | PROT_WRITE | pmap_flags);
                        if (error) {
                                pmap_update(pmap_kernel());
                                km_free((void *)sva, ssize, &kv_any, &kp_none);
                                return (error);
                        }

                        /*
                         * This is redundant with what pmap_enter() did
                         * above, but will take care of forcing other
                         * mappings of the same page (if any) to be
                         * uncached.
                         * If there are no multiple mappings of that
                         * page, this amounts to a noop.
                         */
                        if (flags & (BUS_DMA_COHERENT | BUS_DMA_NOCACHE))
                                pmap_page_cache(PHYS_TO_VM_PAGE(pa),
                                    PGF_UNCACHED);
                }
                pmap_update(pmap_kernel());
        }

        return (0);
}

/*
 * Common function for unmapping DMA-safe memory.  May be called by
 * bus-specific DMA memory unmapping functions.
 */
void
_dmamem_unmap(bus_dma_tag_t t, caddr_t kva, size_t size)
{
        if (IS_XKPHYS((vaddr_t)kva))
                return;

        km_free(kva, round_page(size), &kv_any, &kp_none);
}

/*
 * Common function for mmap(2)'ing DMA-safe memory.  May be called by
 * bus-specific DMA mmap(2)'ing functions.
 */
paddr_t
_dmamem_mmap(bus_dma_tag_t t, bus_dma_segment_t *segs, int nsegs, off_t off,
    int prot, int flags)
{
        int i;

        for (i = 0; i < nsegs; i++) {
#ifdef DIAGNOSTIC
                if (off & PGOFSET)
                        panic("_dmamem_mmap: offset unaligned");
                if (segs[i].ds_addr & PGOFSET)
                        panic("_dmamem_mmap: segment unaligned");
                if (segs[i].ds_len & PGOFSET)
                        panic("_dmamem_mmap: segment size not multiple"
                            " of page size");
#endif
                if (off >= segs[i].ds_len) {
                        off -= segs[i].ds_len;
                        continue;
                }

                return ((*t->_device_to_pa)(segs[i].ds_addr) + off);
        }

        /* Page not found. */
        return (-1);
}

/**********************************************************************
 * DMA utility functions
 **********************************************************************/

/*
 * Utility function to load a linear buffer.  lastaddrp holds state
 * between invocations (for multiple-buffer loads).  segp contains
 * the starting segment on entrance, and the ending segment on exit.
 * first indicates if this is the first invocation of this function.
 */
int
_dmamap_load_buffer(bus_dma_tag_t t, bus_dmamap_t map, void *buf,
    bus_size_t buflen, struct proc *p, int flags, paddr_t *lastaddrp,
    int *segp, int first)
{
        bus_size_t sgsize;
        bus_addr_t lastaddr, baddr, bmask;
        paddr_t curaddr;
        vaddr_t vaddr = (vaddr_t)buf;
        int seg;
        pmap_t pmap;

        if (p != NULL)
                pmap = p->p_vmspace->vm_map.pmap;
        else
                pmap = pmap_kernel();

        lastaddr = *lastaddrp;
        bmask  = ~(map->_dm_boundary - 1);
        if (t->_dma_mask != 0)
                bmask &= t->_dma_mask;

        for (seg = *segp; buflen > 0; ) {
                /*
                 * Get the physical address for this segment.
                 */
                if (pmap_extract(pmap, vaddr, &curaddr) == 0)
                        panic("_dmapmap_load_buffer: pmap_extract(%p, %lx) failed!",
                            pmap, vaddr);

                /*
                 * Compute the segment size, and adjust counts.
                 */
                sgsize = NBPG - ((u_long)vaddr & PGOFSET);
                if (buflen < sgsize)
                        sgsize = buflen;

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

                /*
                 * Insert chunk into a segment, coalescing with
                 * previous segment if possible.
                 */
                if (first) {
                        map->dm_segs[seg].ds_addr =
                            (*t->_pa_to_device)(curaddr);
                        map->dm_segs[seg].ds_len = sgsize;
                        map->dm_segs[seg]._ds_paddr = curaddr;
                        map->dm_segs[seg]._ds_vaddr = vaddr;
                        first = 0;
                } else {
                        if ((bus_addr_t)curaddr == lastaddr &&
                            (map->dm_segs[seg].ds_len + sgsize) <=
                             map->_dm_maxsegsz &&
                             (map->_dm_boundary == 0 ||
                             (map->dm_segs[seg].ds_addr & bmask) ==
                             ((bus_addr_t)curaddr & bmask)))
                                map->dm_segs[seg].ds_len += sgsize;
                        else {
                                if (++seg >= map->_dm_segcnt)
                                        break;
                                map->dm_segs[seg].ds_addr =
                                    (*t->_pa_to_device)(curaddr);
                                map->dm_segs[seg].ds_len = sgsize;
                                map->dm_segs[seg]._ds_paddr = curaddr;
                                map->dm_segs[seg]._ds_vaddr = vaddr;
                        }
                }

                lastaddr = (bus_addr_t)curaddr + sgsize;
                vaddr += sgsize;
                buflen -= sgsize;
        }

        *segp = seg;
        *lastaddrp = lastaddr;

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

        return (0);
}

/*
 * Allocate physical memory from the given physical address range.
 * Called by DMA-safe memory allocation methods.
 */
int
_dmamem_alloc_range(bus_dma_tag_t t, bus_size_t size, bus_size_t alignment,
    bus_size_t boundary, bus_dma_segment_t *segs, int nsegs, int *rsegs,
    int flags, paddr_t low, paddr_t high)
{
        paddr_t curaddr, lastaddr;
        vm_page_t m;
        struct pglist mlist;
        int curseg, error, plaflag;

        /* Always round the size. */
        size = round_page(size);

        /*
         * Allocate pages from the VM system.
         */
        plaflag = flags & BUS_DMA_NOWAIT ? UVM_PLA_NOWAIT : UVM_PLA_WAITOK;
        if (flags & BUS_DMA_ZERO)
                plaflag |= UVM_PLA_ZERO;

        TAILQ_INIT(&mlist);
        error = uvm_pglistalloc(size, low, high, alignment, boundary,
            &mlist, nsegs, plaflag);
        if (error)
                return (error);

        /*
         * Compute the location, size, and number of segments actually
         * returned by the VM code.
         */
        m = TAILQ_FIRST(&mlist);
        curseg = 0;
        lastaddr = segs[curseg].ds_addr =
            (*t->_pa_to_device)(VM_PAGE_TO_PHYS(m));
        segs[curseg].ds_len = PAGE_SIZE;
        m = TAILQ_NEXT(m, pageq);

        for (; m != NULL; m = TAILQ_NEXT(m, pageq)) {
                curaddr = VM_PAGE_TO_PHYS(m);
#ifdef DIAGNOSTIC
                if (curaddr < low || curaddr >= high) {
                        printf("vm_page_alloc_memory returned non-sensical"
                            " address 0x%lx\n", curaddr);
                        panic("_dmamem_alloc_range");
                }
#endif
                curaddr = (*t->_pa_to_device)(curaddr);
                if (curaddr == (lastaddr + PAGE_SIZE))
                        segs[curseg].ds_len += PAGE_SIZE;
                else {
                        curseg++;
                        segs[curseg].ds_addr = curaddr;
                        segs[curseg].ds_len = PAGE_SIZE;
                }
                lastaddr = curaddr;
        }

        *rsegs = curseg + 1;

        return (0);
}