xref: /src/sys/arch/vax/vax/bus_dma.c

/*	$NetBSD: bus_dma.c,v 1.29 2008/02/03 08:34:57 matt Exp $	*/

/*-
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the NetBSD
 *	Foundation, Inc. and its contributors.
 * 4. Neither the name of The NetBSD Foundation nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * 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.
 */
/*
 * bus_dma routines for vax. File copied from arm32/bus_dma.c.
 * NetBSD: bus_dma.c,v 1.11 1998/09/21 22:53:35 thorpej Exp
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: bus_dma.c,v 1.29 2008/02/03 08:34:57 matt Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/reboot.h>
#include <sys/conf.h>
#include <sys/file.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/vnode.h>
#include <sys/device.h>

#include <uvm/uvm_extern.h>

#define _VAX_BUS_DMA_PRIVATE
#include <machine/bus.h>

#include <machine/ka43.h>
#include <machine/sid.h>

extern	paddr_t avail_start, avail_end;
extern  vaddr_t virtual_avail;

int	_bus_dmamap_load_buffer __P((bus_dma_tag_t, bus_dmamap_t, void *,
	    bus_size_t, struct vmspace *, int, vaddr_t *, int *, int));
int	_bus_dma_inrange __P((bus_dma_segment_t *, int, bus_addr_t));
int	_bus_dmamem_alloc_range __P((bus_dma_tag_t, bus_size_t, bus_size_t,
	    bus_size_t, bus_dma_segment_t*, int, int *, int, vaddr_t, vaddr_t));
/*
 * Common function for DMA map creation.  May be called by bus-specific
 * DMA map creation functions.
 */
int
_bus_dmamap_create(t, size, nsegments, maxsegsz, boundary, flags, dmamp)
	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 vax_bus_dmamap *map;
	void *mapstore;
	size_t mapsize;

#ifdef DEBUG_DMA
	printf("dmamap_create: t=%p size=%lx nseg=%x msegsz=%lx boundary=%lx flags=%x\n",
	    t, size, nsegments, maxsegsz, boundary, flags);
#endif	/* DEBUG_DMA */

	/*
	 * 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 vax_bus_dmamap) +
	    (sizeof(bus_dma_segment_t) * (nsegments - 1));
	if ((mapstore = malloc(mapsize, M_DMAMAP,
	    (flags & BUS_DMA_NOWAIT) ? M_NOWAIT : M_WAITOK)) == NULL)
		return (ENOMEM);

	bzero(mapstore, mapsize);
	map = (struct vax_bus_dmamap *)mapstore;
	map->_dm_size = size;
	map->_dm_segcnt = nsegments;
	map->_dm_maxmaxsegsz = maxsegsz;
	map->_dm_boundary = boundary;
	map->_dm_flags = flags & ~(BUS_DMA_WAITOK|BUS_DMA_NOWAIT);
	map->dm_maxsegsz = maxsegsz;
	map->dm_mapsize = 0;		/* no valid mappings */
	map->dm_nsegs = 0;

	*dmamp = map;
#ifdef DEBUG_DMA
	printf("dmamap_create:map=%p\n", map);
#endif	/* DEBUG_DMA */
	return (0);
}

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

#ifdef DEBUG_DMA
	printf("dmamap_destroy: t=%p map=%p\n", t, map);
#endif	/* DEBUG_DMA */
#ifdef DIAGNOSTIC
	if (map->dm_nsegs > 0)
		printf("bus_dmamap_destroy() called for map with valid mappings\n");
#endif	/* DIAGNOSTIC */
	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
_bus_dmamap_load(t, map, buf, buflen, p, flags)
	bus_dma_tag_t t;
	bus_dmamap_t map;
	void *buf;
	bus_size_t buflen;
	struct proc *p;
	int flags;
{
	vaddr_t lastaddr = 0;
	int seg, error;
	struct vmspace *vm;

#ifdef DEBUG_DMA
	printf("dmamap_load: t=%p map=%p buf=%p len=%lx p=%p f=%d\n",
	    t, map, buf, buflen, p, flags);
#endif	/* DEBUG_DMA */

	/*
	 * Make sure that on error condition we return "no valid mappings".
	 */
	map->dm_mapsize = 0;
	map->dm_nsegs = 0;
	KASSERT(map->dm_maxsegsz <= map->_dm_maxmaxsegsz);

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

	if (p != NULL) {
		vm = p->p_vmspace;
	} else {
		vm = vmspace_kernel();
	}

	seg = 0;
	error = _bus_dmamap_load_buffer(t, map, buf, buflen, vm, flags,
	    &lastaddr, &seg, 1);
	if (error == 0) {
		map->dm_mapsize = buflen;
		map->dm_nsegs = seg + 1;
	}
#ifdef DEBUG_DMA
	printf("dmamap_load: error=%d\n", error);
#endif	/* DEBUG_DMA */
	return (error);
}

/*
 * Like _bus_dmamap_load(), but for mbufs.
 */
int
_bus_dmamap_load_mbuf(t, map, m0, flags)
	bus_dma_tag_t t;
	bus_dmamap_t map;
	struct mbuf *m0;
	int flags;
{
	vaddr_t lastaddr = 0;
	int seg, error;
	bool first;
	struct mbuf *m;

#ifdef DEBUG_DMA
	printf("dmamap_load_mbuf: t=%p map=%p m0=%p f=%d\n",
	    t, map, m0, flags);
#endif	/* DEBUG_DMA */

	/*
	 * Make sure that on error condition we return "no valid mappings."
	 */
	map->dm_mapsize = 0;
	map->dm_nsegs = 0;
	KASSERT(map->dm_maxsegsz <= map->_dm_maxmaxsegsz);

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

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

	first = true;
	seg = 0;
	error = 0;
	for (m = m0; m != NULL && error == 0; m = m->m_next, first = false) {
		if (m->m_len == 0)
			continue;
#if 0
		switch (m->m_flags & (M_EXT|M_CLUSTER)) {
#if 0
		case M_EXT|M_CLUSTER:
			KASSERT(m->m_ext.ext_paddr != M_PADDR_INVALID);
			lastaddr = m->m_ext.ext_paddr
			    + (m->m_data - m->m_ext.ext_buf);
#endif
#if 1
    have_addr:
#endif
			if (!first && ++seg >= map->_dm_segcnt) {
				error = EFBIG;
				continue;
			}
			map->dm_segs[seg].ds_addr = lastaddr;
			map->dm_segs[seg].ds_len = m->m_len;
			lastaddr += m->m_len;
			continue;
#if 1
		case 0:
			KASSERT(m->m_paddr != M_PADDR_INVALID);
			lastaddr = m->m_paddr + M_BUFOFFSET(m)
			    + (m->m_data - M_BUFADDR(m));
			goto have_addr;
#endif
		default:
			break;
		}
#endif
		error = _bus_dmamap_load_buffer(t, map, m->m_data, m->m_len,
		    vmspace_kernel(), flags, &lastaddr, &seg, first);
	}
	if (error == 0) {
		map->dm_mapsize = m0->m_pkthdr.len;
		map->dm_nsegs = seg + 1;
	}
#ifdef DEBUG_DMA
	printf("dmamap_load_mbuf: error=%d\n", error);
#endif	/* DEBUG_DMA */
	return (error);
}

/*
 * Like _bus_dmamap_load(), but for uios.
 */
int
_bus_dmamap_load_uio(t, map, uio, flags)
	bus_dma_tag_t t;
	bus_dmamap_t map;
	struct uio *uio;
	int flags;
{
	vaddr_t lastaddr = 0;
	int seg, i, error;
	bool first;
	bus_size_t minlen, resid;
	struct iovec *iov;
	void *addr;

	/*
	 * Make sure that on error condition we return "no valid mappings."
	 */
	map->dm_mapsize = 0;
	map->dm_nsegs = 0;
	KASSERT(map->dm_maxsegsz <= map->_dm_maxmaxsegsz);

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

	first = true;
	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 = _bus_dmamap_load_buffer(t, map, addr, minlen,
		    uio->uio_vmspace, flags, &lastaddr, &seg, first);
		first = false;

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

/*
 * Like _bus_dmamap_load(), but for raw memory allocated with
 * bus_dmamem_alloc().
 */
int
_bus_dmamap_load_raw(t, map, segs, nsegs, size, flags)
	bus_dma_tag_t t;
	bus_dmamap_t map;
	bus_dma_segment_t *segs;
	int nsegs;
	bus_size_t size;
	int flags;
{

	panic("_bus_dmamap_load_raw: not implemented");
}

/*
 * Common function for unloading a DMA map.  May be called by
 * bus-specific DMA map unload functions.
 */
void
_bus_dmamap_unload(t, map)
	bus_dma_tag_t t;
	bus_dmamap_t map;
{

#ifdef DEBUG_DMA
	printf("dmamap_unload: t=%p map=%p\n", t, map);
#endif	/* DEBUG_DMA */

	/*
	 * No resources to free; just mark the mappings as
	 * invalid.
	 */
	map->dm_maxsegsz = map->_dm_maxmaxsegsz;
	map->dm_mapsize = 0;
	map->dm_nsegs = 0;
}

/*
 * Common function for DMA map synchronization.  May be called
 * by bus-specific DMA map synchronization functions.
 */
void
_bus_dmamap_sync(t, map, offset, len, ops)
	bus_dma_tag_t t;
	bus_dmamap_t map;
	bus_addr_t offset;
	bus_size_t len;
	int ops;
{
#ifdef DEBUG_DMA
	printf("dmamap_sync: t=%p map=%p offset=%lx len=%lx ops=%x\n",
	    t, map, offset, len, ops);
#endif	/* DEBUG_DMA */
	/*
	 * A vax only has snoop-cache, so this routine is a no-op.
	 */
	return;
}

/*
 * Common function for DMA-safe memory allocation.  May be called
 * by bus-specific DMA memory allocation functions.
 */

int
_bus_dmamem_alloc(t, size, alignment, boundary, segs, nsegs, rsegs, flags)
	bus_dma_tag_t t;
	bus_size_t size, alignment, boundary;
	bus_dma_segment_t *segs;
	int nsegs;
	int *rsegs;
	int flags;
{
	int error;

	error =  (_bus_dmamem_alloc_range(t, size, alignment, boundary,
	    segs, nsegs, rsegs, flags, round_page(avail_start),
	    trunc_page(avail_end)));
	return(error);
}

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

#ifdef DEBUG_DMA
	printf("dmamem_free: t=%p segs=%p nsegs=%x\n", t, segs, nsegs);
#endif	/* DEBUG_DMA */

	/*
	 * 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(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
_bus_dmamem_map(t, segs, nsegs, size, kvap, flags)
	bus_dma_tag_t t;
	bus_dma_segment_t *segs;
	int nsegs;
	size_t size;
	void **kvap;
	int flags;
{
	vaddr_t va;
	bus_addr_t addr;
	int curseg;
	const uvm_flag_t kmflags =
	    (flags & BUS_DMA_NOWAIT) != 0 ? UVM_KMF_NOWAIT : 0;

	/*
	 * Special case (but common):
	 * If there is only one physical segment then the already-mapped
	 * virtual address is returned, since all physical memory is already
	 * in the beginning of kernel virtual memory.
	 */
	if (nsegs == 1) {
		*kvap = (void *)(segs[0].ds_addr | KERNBASE);
		/*
		 * KA43 (3100/m76) must have its DMA-safe memory accessed
		 * through DIAGMEM. Remap it here.
		 */
		if (vax_boardtype == VAX_BTYP_43) {
			pmap_map((vaddr_t)*kvap, segs[0].ds_addr|KA43_DIAGMEM,
			    (segs[0].ds_addr|KA43_DIAGMEM) + size,
			    VM_PROT_READ|VM_PROT_WRITE);
		}
		return 0;
	}
	size = round_page(size);
	va = uvm_km_alloc(kernel_map, size, 0, UVM_KMF_VAONLY | kmflags);

	if (va == 0)
		return (ENOMEM);

	*kvap = (void *)va;

	for (curseg = 0; curseg < nsegs; curseg++) {
		for (addr = segs[curseg].ds_addr;
		    addr < (segs[curseg].ds_addr + segs[curseg].ds_len);
		    addr += PAGE_SIZE, va += PAGE_SIZE, size -= PAGE_SIZE) {
			if (size == 0)
				panic("_bus_dmamem_map: size botch");
			if (vax_boardtype == VAX_BTYP_43)
				addr |= KA43_DIAGMEM;
			pmap_enter(pmap_kernel(), va, addr,
			    VM_PROT_READ | VM_PROT_WRITE,
			    VM_PROT_READ | VM_PROT_WRITE | PMAP_WIRED);
		}
	}
	pmap_update(pmap_kernel());
	return (0);
}

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

#ifdef DEBUG_DMA
	printf("dmamem_unmap: t=%p kva=%p size=%x\n", t, kva, size);
#endif	/* DEBUG_DMA */
#ifdef DIAGNOSTIC
	if ((u_long)kva & PGOFSET)
		panic("_bus_dmamem_unmap");
#endif	/* DIAGNOSTIC */

	/* Avoid free'ing if not mapped */
	if (kva < (void *)virtual_avail)
		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, UVM_KMF_VAONLY);
}

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

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

		return (btop((u_long)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 entrace, and the ending segment on exit.
 * first indicates if this is the first invocation of this function.
 */
int
_bus_dmamap_load_buffer(t, map, buf, buflen, vm, flags, lastaddrp, segp, first)
	bus_dma_tag_t t;
	bus_dmamap_t map;
	void *buf;
	bus_size_t buflen;
	struct vmspace *vm;
	int flags;
	vaddr_t *lastaddrp;
	int *segp;
	bool first;
{
	bus_size_t sgsize;
	bus_addr_t curaddr, lastaddr, baddr, bmask;
	vaddr_t vaddr = (vaddr_t)buf;
	int seg;
	pmap_t pmap;

#ifdef DEBUG_DMA
	printf("_bus_dmamem_load_buffer(buf=%p, len=%lx, flags=%d, 1st=%d)\n",
	    buf, buflen, flags, first);
#endif	/* DEBUG_DMA */

	pmap = vm_map_pmap(&vm->vm_map);

	lastaddr = *lastaddrp;
	bmask  = ~(map->_dm_boundary - 1);

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

#if 0
		/*
		 * Make sure we're in an allowed DMA range.
		 */
		if (t->_ranges != NULL &&
		    _bus_dma_inrange(t->_ranges, t->_nranges, curaddr) == 0)
			return (EINVAL);
#endif

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

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

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

		lastaddr = 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);
}

/*
 * Check to see if the specified page is in an allowed DMA range.
 */
int
_bus_dma_inrange(ranges, nranges, curaddr)
	bus_dma_segment_t *ranges;
	int nranges;
	bus_addr_t curaddr;
{
	bus_dma_segment_t *ds;
	int i;

	for (i = 0, ds = ranges; i < nranges; i++, ds++) {
		if (curaddr >= ds->ds_addr &&
		    round_page(curaddr) <= (ds->ds_addr + ds->ds_len))
			return (1);
	}

	return (0);
}

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

#ifdef DEBUG_DMA
	printf("alloc_range: t=%p size=%lx align=%lx boundary=%lx segs=%p nsegs=%x rsegs=%p flags=%x lo=%lx hi=%lx\n",
	    t, size, alignment, boundary, segs, nsegs, rsegs, flags, low, high);
#endif	/* DEBUG_DMA */

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

	/*
	 * Allocate pages from the VM system.
	 */
	error = uvm_pglistalloc(size, low, high, alignment, boundary,
	    &mlist, nsegs, (flags & BUS_DMA_NOWAIT) == 0);
	if (error)
		return (error);

	/*
	 * Compute the location, size, and number of segments actually
	 * returned by the VM code.
	 */
	m = mlist.tqh_first;
	curseg = 0;
	lastaddr = segs[curseg].ds_addr = VM_PAGE_TO_PHYS(m);
	segs[curseg].ds_len = PAGE_SIZE;
#ifdef DEBUG_DMA
		printf("alloc: page %lx\n", lastaddr);
#endif	/* DEBUG_DMA */
	m = m->pageq.tqe_next;

	for (; m != NULL; m = m->pageq.tqe_next) {
		curaddr = VM_PAGE_TO_PHYS(m);
#ifdef DIAGNOSTIC
		if (curaddr < low || curaddr >= high) {
			printf("uvm_pglistalloc returned non-sensical"
			    " address 0x%lx\n", curaddr);
			panic("_bus_dmamem_alloc_range");
		}
#endif	/* DIAGNOSTIC */
#ifdef DEBUG_DMA
		printf("alloc: page %lx\n", curaddr);
#endif	/* DEBUG_DMA */
		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);
}

/*
 * "generic" DMA struct, nothing special.
 */
struct vax_bus_dma_tag vax_bus_dma_tag = {
	NULL,
	0,
	0,
	0,
	0,
	0,
	_bus_dmamap_create,
	_bus_dmamap_destroy,
	_bus_dmamap_load,
	_bus_dmamap_load_mbuf,
	_bus_dmamap_load_uio,
	_bus_dmamap_load_raw,
	_bus_dmamap_unload,
	_bus_dmamap_sync,
	_bus_dmamem_alloc,
	_bus_dmamem_free,
	_bus_dmamem_map,
	_bus_dmamem_unmap,
	_bus_dmamem_mmap,
};