By popular demand and peer pressure, check-in work in progress work to support

the Yeelong Lemote mips-based netbook. Kernel bits only for now, needs
polishing; most of this work done during h2k9 last month, although the
porting effort started earlier this year.

1 files changed, 695 insertions, 0 deletions

diff --git a/sys/arch/loongson/loongson/bus_dma.c b/sys/arch/loongson/loongson/bus_dma.c
new file mode 100644
index 00000000000..b47df55f4f1
--- /dev/null
+++ b/sys/arch/loongson/loongson/bus_dma.c
@@ -0,0 +1,695 @@
+/*	$OpenBSD: bus_dma.c,v 1.1 2009/12/11 17:23:29 miod 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 <sys/user.h>
+
+#include <uvm/uvm_extern.h>
+
+#include <mips64/archtype.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)
+{
+	free(map, M_DEVBUF);
+}
+
+/*
+ * 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)
+{
+	if (nsegs > map->_dm_segcnt || size > map->_dm_size)
+		return (EINVAL);
+
+	/*
+	 * Make sure we don't cross any boundaries.
+	 */
+	if (map->_dm_boundary) {
+		bus_addr_t bmask = ~(map->_dm_boundary - 1);
+		int i;
+
+		if (t->_dma_mask != 0)
+			bmask &= t->_dma_mask;
+		for (i = 0; i < nsegs; i++) {
+			if (segs[i].ds_len > map->_dm_maxsegsz)
+				return (EINVAL);
+			if ((segs[i].ds_addr & bmask) !=
+			    ((segs[i].ds_addr + segs[i].ds_len - 1) & bmask))
+				return (EINVAL);
+		}
+	}
+
+	bcopy(segs, map->dm_segs, nsegs * sizeof(*segs));
+	map->dm_nsegs = nsegs;
+	map->dm_mapsize = size;
+	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)
+{
+#define SYNC_R 0	/* WB invalidate, WT invalidate */
+#define SYNC_W 1	/* WB writeback, WT unaffected */
+#define SYNC_X 2	/* WB writeback + invalidate, WT invalidate */
+	int nsegs;
+	int curseg;
+	int cacheop;
+
+	nsegs = map->dm_nsegs;
+	curseg = 0;
+
+	while (size && nsegs) {
+		vaddr_t vaddr;
+		paddr_t paddr;
+		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)
+					cacheop = SYNC_X;
+				else
+					cacheop = SYNC_W;
+			} else
+#if 0
+			if (op & (BUS_DMASYNC_PREREAD | BUS_DMASYNC_POSTREAD))
+				cacheop = SYNC_R;
+#else
+			if (op & BUS_DMASYNC_PREREAD)
+				cacheop = SYNC_X;
+			else if (op & BUS_DMASYNC_POSTREAD)
+				cacheop = SYNC_R;
+#endif
+			else
+				cacheop = -1;
+			if (cacheop >= 0) {
+				Mips_IOSyncDCache(vaddr, paddr, ssize, cacheop);
+			}
+			size -= ssize;
+		}
+		curseg++;
+		nsegs--;
+	}
+
+#ifdef DIAGNOSTIC
+	if (size != 0) {
+		panic("_dmamap_sync: ran off map!");
+	}
+#endif
+}
+
+/*
+ * 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, (vaddr_t)0, (vaddr_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;
+	paddr_t pa;
+	bus_addr_t addr;
+	int curseg;
+
+	if (nsegs == 1) {
+		pa = (*t->_device_to_pa)(segs[0].ds_addr);
+		if (flags & BUS_DMA_COHERENT)
+			*kvap = (caddr_t)PHYS_TO_UNCACHED(pa);
+		else
+			*kvap = (caddr_t)PHYS_TO_XKPHYS(pa, CCA_CACHED);
+		return (0);
+	}
+
+	size = round_page(size);
+	va = uvm_km_valloc(kernel_map, size);
+	if (va == 0)
+		return (ENOMEM);
+
+	*kvap = (caddr_t)va;
+
+	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);
+			pmap_enter(pmap_kernel(), va, pa,
+			    VM_PROT_READ | VM_PROT_WRITE,
+			    VM_PROT_READ | VM_PROT_WRITE | PMAP_WIRED);
+
+			if (flags & BUS_DMA_COHERENT)
+				pmap_page_cache(PHYS_TO_VM_PAGE(pa),
+				    PV_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;
+
+	size = round_page(size);
+	pmap_remove(pmap_kernel(), (vaddr_t)kva, (vaddr_t)kva + size);
+	pmap_update(pmap_kernel());
+	uvm_km_free(kernel_map, (vaddr_t)kva, size);
+}
+
+/*
+ * 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 (atop((*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) == FALSE)
+			panic("_dmapmap_load_buffer: pmap_extract(%x, %x) 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, vaddr_t low, vaddr_t high)
+{
+	vaddr_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 != TAILQ_END(&mlist); 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);
+}