800 lines
24 KiB
Groff
800 lines
24 KiB
Groff
.\" Copyright (c) 2002, 2003 Hiten M. Pandya.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions, and the following disclaimer,
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.\" without modification, immediately at the beginning of the file.
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.\" 2. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR, CONTRIBUTORS OR THE
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.\" VOICES IN HITEN PANDYA'S HEAD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
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.\" TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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.\" PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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.\" LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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.\" NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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.\" SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" Copyright (c) 1996, 1997, 1998, 2001 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
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.\" NASA Ames Research Center.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgment:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\" $NetBSD: bus_dma.9,v 1.25 2002/10/14 13:43:16 wiz Exp $
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.\"
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.Dd May 28, 2003
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.Dt BUS_DMA 9
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.Os
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.Sh NAME
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.Nm bus_dma ,
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.Nm bus_dma_tag_create ,
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.Nm bus_dma_tag_destroy ,
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.Nm bus_dmamap_create ,
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.Nm bus_dmamap_destroy ,
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.Nm bus_dmamap_load ,
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.Nm bus_dmamap_load_mbuf ,
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.Nm bus_dmamap_load_uio ,
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.Nm bus_dmamap_unload ,
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.Nm bus_dmamap_sync ,
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.Nm bus_dmamem_alloc ,
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.Nm bus_dmamem_free
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.Nd Bus and Machine Independent DMA Mapping Interface
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.Sh SYNOPSIS
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.In machine/bus.h
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.Ft int
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.Fn bus_dma_tag_create "bus_dma_tag_t parent" "bus_size_t alignment" \
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"bus_size_t boundary" "bus_addr_t lowaddr" "bus_addr_t highaddr" \
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"bus_dma_filter_t *filtfunc" "void *filtfuncarg" "bus_size_t maxsize" \
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"int nsegments" "bus_size_t maxsegsz" "int flags" "bus_dma_lock_t *lockfunc" \
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"void *lockfuncarg" "bus_dma_tag_t *dmat"
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.Ft int
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.Fn bus_dma_tag_destroy "bus_dma_tag_t dmat"
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.Ft int
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.Fn bus_dmamap_create "bus_dma_tag_t dmat" "int flags" "bus_dmamap_t *mapp"
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.Ft int
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.Fn bus_dmamap_destroy "bus_dma_tag_t dmat" "bus_dmamap_t map"
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.Ft int
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.Fn bus_dmamap_load "bus_dma_tag_t dmat" "bus_dmamap_t map" "void *buf" \
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"bus_size_t buflen" "bus_dmamap_callback_t *callback" "void *callback_arg" \
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"int flags"
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.Ft int
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.Fn bus_dmamap_load_mbuf "bus_dma_tag_t dmat" "bus_dmamap_t map" \
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"struct mbuf *mbuf" "bus_dmamap_callback2_t *callback" "void *callback_arg" \
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"int flags"
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.Ft int
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.Fn bus_dmamap_load_uio "bus_dma_tag_t dmat" "bus_dmamap_t map" \
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"struct uio *uio" "bus_dmamap_callback2_t *callback" "void *callback_arg" \
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"int flags"
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.Ft void
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.Fn bus_dmamap_unload "bus_dma_tag_t dmat" "bus_dmamap_t map"
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.Ft void
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.Fn bus_dmamap_sync "bus_dma_tag_t dmat" "bus_dmamap_t map" \
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"op"
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.Ft int
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.Fn bus_dmamem_alloc "bus_dma_tag_t dmat" "void **vaddr" \
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"int flags" "bus_dmamap_t *mapp"
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.Ft void
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.Fn bus_dmamem_free "bus_dma_tag_t dmat" "void *vaddr" \
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"bus_dmamap_t map"
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.Sh DESCRIPTION
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Direct Memory Access (DMA) is a method of transferring data
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without involving the CPU, thus providing higher performance.
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A DMA transaction can be achieved between device to memory,
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device to device, or memory to memory.
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.Pp
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The
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.Nm
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API is a bus, device, and machine-independent (MI) interface to
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DMA mechanisms.
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It provides the client with flexibility and simplicity by
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abstracting machine dependent issues like setting up
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DMA mappings, handling cache issues, bus specific features
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and limitations.
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.Sh STRUCTURES AND TYPES
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.Bl -tag -width compact
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.It Vt bus_dma_tag_t
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A machine-dependent (MD) opaque type that describes the
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characteristics of DMA transactions.
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DMA tags are organized into a hierarchy, with each child
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tag inheriting the restrictions of its parent.
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This allows all devices along the path of DMA transactions
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to contribute to the constraints of those transactions.
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.It Vt bus_dma_filter_t
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Client specified address filter having the format:
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.Bl -tag -width compact
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.It Ft int
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.Fn "client_filter" "void *filtarg" "bus_addr_t testaddr"
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.El
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.sp
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Address filters can be specified during tag creation to allow
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for devices who's DMA address restrictions cannot be specified
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by a single window.
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The
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.Fa filtarg
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is client specified during tag creation to be passed to all
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invocations of the callback.
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The
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.Fa testaddr
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argument contains a potential starting address of a DMA mapping.
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The filter function operates on the set of addresses from
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.Fa testaddr
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to
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.Ql trunc_page(testaddr) + PAGE_SIZE - 1 ,
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inclusive.
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The filter function should return zero for any mapping in this range
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that can be accommodated by the device and non-zero otherwise.
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.It Vt bus_dma_segment_t
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A machine-dependent type that describes individual
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DMA segments.
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.Bd -literal
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bus_addr_t ds_addr;
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bus_size_t ds_len;
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.Ed
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.sp
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The
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.Fa ds_addr
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field contains the device visible address of the DMA segment, and
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.Fa ds_len
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contains the length of the DMA segment.
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Although the DMA segments returned by a mapping call will adhere to
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all restrictions necessary for a successful DMA operation, some conversion
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(e.g.\& a conversion from host byte order to the device's byte order) is
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almost always required when presenting segment information to the device.
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.It Vt bus_dmamap_t
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A machine-dependent opaque type describing an individual mapping.
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Multiple DMA maps can be associated with one DMA tag.
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.It Vt bus_dmamap_callback_t
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Client specified callback for receiving mapping information resulting from
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the load of a
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.Vt bus_dmamap_t
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via
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.Fn bus_dmamap_load .
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Callbacks are of the format:
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.Bl -tag -width compact
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.It Ft void
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.Fn "client_callback" "void *callback_arg" "bus_dma_segment_t *segs" \
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"int nseg" "int error"
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.El
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.sp
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The
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.Fa callback_arg
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is the callback argument passed to dmamap load functions.
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The
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.Fa segs
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and
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.Fa nseg
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parameters describe an array of
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.Vt bus_dma_segment_t
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structures that represent the mapping.
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This array is only valid within the scope of the callback function.
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The success or failure of the mapping is indicated by the
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.Fa error
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parameter.
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More information on the use of callbacks can be found in the
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description of the individual dmamap load functions.
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.It Vt bus_dmamap_callback2_t
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Client specified callback for receiving mapping information resulting from
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the load of a
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.Vt bus_dmamap_t
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via
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.Fn bus_dmamap_load_uio
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or
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.Fn bus_dmamap_load_mbuf .
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.sp
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Callback2s are of the format:
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.Bl -tag -width compact
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.It Ft void
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.Fn "client_callback2" "void *callback_arg" "bus_dma_segment_t *segs" \
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"int nseg" "bus_size_t mapsize" "int error"
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.El
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.sp
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Callback2's behavior is the same as
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.Vt bus_dmamap_callback_t
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with the addition that the length of the data mapped is provided via
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.Fa mapsize .
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.It Vt bus_dmasync_op_t
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Memory synchronization operation specifier.
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Bus DMA requires explicit synchronization of memory with it's device
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visible mapping in order to guarantee memory coherency.
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The
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.Vt bus_dmasync_op_t
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allows the type of DMA operation that will be or has been performed
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to be communicated to the system so that the correct coherency measures
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are taken.
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All operations specified below are performed from the CPU's
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point of view (for a complete description, see the
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.Fn bus_dmamap_sync
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description below):
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.Bl -tag -width BUS_DMASYNC_POSTWRITE
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.It Dv BUS_DMASYNC_PREREAD
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Perform any synchronization required after an update of memory by the CPU
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but prior to DMA read operations.
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.It Dv BUS_DMASYNC_PREWRITE
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Perform any synchronization required after an update of memory by the CPU
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but prior to DMA write operations.
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.It Dv BUS_DMASYNC_PREREAD|BUS_DMASYNC_PREWRITE
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Perform any synchronization required prior to a combination of DMA read
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and write operations.
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.It Dv BUS_DMASYNC_POSTREAD
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Perform any synchronization required after DMA read operations, but prior
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to CPU access of the memory.
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.It Dv BUS_DMASYNC_POSTWRITE
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Perform any synchronization required after DMA write operations, but prior
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to CPU access of the memory.
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.It Dv BUS_DMASYNC_POSTREAD|BUS_DMASYNC_POSTWRITE
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Perform any synchronization required after a combination of DMA read
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and write operations.
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.El
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.It Vt bus_dma_lock_t
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Client specified lock/mutex manipulation method.
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This will be called from
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within busdma whenever a client lock needs to be manipulated.
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In its current form, the function will be called immediately before
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the callback for a dma load operation that has been deferred with
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.Dv BUS_DMA_LOCK
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and immediately after with
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.Dv BUS_DMA_UNLOCK .
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If the load operation does not need to be deferred, then it
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will not be called since the function loading the map should
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be holding the appropriate locks.
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This method is of the format:
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.Bl -tag -width compact
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.It Ft void
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.Fn "lockfunc" "void *lockfunc_arg" "bus_dma_lock_op_t op"
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.El
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.sp
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Two
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.Vt lockfunc
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implementations are provided for convenience.
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.Fn busdma_lock_mutex
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performs standard mutex operations on the sleep mutex provided via the
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.Fa lockfuncarg .
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passed into
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.Fn bus_dma_tag_create .
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.Fn dflt_lock
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will generate a system panic if it is called.
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It is substituted into the tag when
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.Fa lockfunc
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is passed as NULL to
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.Fn bus_dma_tag_create .
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.It Vt bus_dma_lock_op_t
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Operations to be performed by the client-specified
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.Fn lockfunc .
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.Bl -tag -width BUS_DMA_UNLOCK
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.It Dv BUS_DMA_LOCK
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Acquires and/or locks the client locking primitive.
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.It Dv BUS_DMA_UNLOCK
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Releases and/or unlocks the client locking primitive.
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.El
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.El
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.sp
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.Sh FUNCTIONS
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.Bl -tag -width compact
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.It Fn bus_dma_tag_create "parent" "alignment" "boundary" "lowaddr" \
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"highaddr" "*filtfunc" "*filtfuncarg" "maxsize" "nsegments" "maxsegsz" \
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"flags" "lockfunc" "lockfuncarg" "*dmat"
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Allocates a device specific DMA tag, and initializes it according to
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the arguments provided:
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.Bl -tag -width *filtfuncarg -compact
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.It Fa parent
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Indicates restrictions between the parent bridge, CPU memory, and the
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device.
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May be NULL, if no DMA restrictions are to be inherited.
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.It Fa alignment
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Alignment constraint, in bytes, of any mappings created using this tag.
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The alignment must be a power of 2.
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Hardware that can DMA starting at any address would specify
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.Em 1
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for byte alignment.
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Hardware requiring DMA transfers to start on a multiple of 4K
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would specify
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.Em 4096.
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.It Fa boundary
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Boundary constraint, in bytes, of the target DMA memory region.
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The boundary indicates the set of addresses, all multiples of the
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boundary argument, that cannot be crossed by a single
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.Vt bus_dma_segment_t .
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The boundary must be a power of 2 and must be no smaller that the
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maximum segment size.
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.Ql 0
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indicates that there are no boundary restrictions.
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.It Fa lowaddr
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.It Fa highaddr
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Bounds of the window of bus address space that
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.Em cannot
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be directly accessed by the device.
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The window contains all address greater than lowaddr and
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less than or equal to highaddr.
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For example, a device incapable of DMA above 4GB, would specify
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a highaddr of
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.Dv BUS_SPACE_MAXADDR
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and a lowaddr of
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.Dv BUS_SPACE_MAXADDR_32BIT .
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Similarly a device that can only dma to addresses bellow 16MB would
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specify a highaddr of
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.Dv BUS_SPACE_MAXADDR
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and a lowaddr of
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.Dv BUS_SPACE_MAXADDR_24BIT .
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Some implementations requires that some region of device visible
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address space, overlapping available host memory, be outside the
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window.
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This area of
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.Ql safe memory
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is used to bounce requests that would otherwise conflict with
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the exclusion window.
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.It Fa filtfunc
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Optional filter function (may be NULL) to be called for any attempt to
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map memory into the window described by
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.Fa lowaddr
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and
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.Fa highaddr.
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A filter function is only required when the single window described
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by
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.Fa lowaddr
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and
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.Fa highaddr
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cannot adequately describe the constraints of the device.
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The filter function will be called for every machine page
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that overlaps the exclusion window.
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.It Fa filtfuncarg
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Argument passed to all calls to the filter function for this tag.
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May be NULL.
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.It Fa maxsize
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Maximum size, in bytes, of the sum of all segment lengths in a given
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DMA mapping associated with this tag.
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.It Fa nsegments
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Number of discontinuities (scatter/gather segments) allowed
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in a DMA mapped region.
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If there is no restriction,
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.Dv BUS_SPACE_UNRESTRICTED
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may be specified.
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.It Fa maxsegsz
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Maximum size, in bytes, of a segment in any DMA mapped region associated
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with
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.Fa dmat .
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.It Fa flags
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Are as follows:
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.Bl -tag -width "BUS_DMA_ALLOCNOW" -compact
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.It Dv BUS_DMA_ALLOCNOW
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Pre-allocate enough resources to handle at least one map load operation on
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this tag without blocking.
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If sufficient resources are not available,
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.Er ENOMEM
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is returned.
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This should not be used for tags that will not be directly associated with
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a map.
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.El
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.It Fa lockfunc
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Optional lock manipulation function (may be NULL) to be called when busdma
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needs to manipulate a lock on behalf of the client.
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If NULL is specified,
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.Fn dflt_lock
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is used.
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.It Fa lockfuncarg
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Optional argument to be passed to the function specified by
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.Fa lockfunc .
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.It Fa dmat
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Pointer to a bus_dma_tag_t where the resulting DMA tag will
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be stored.
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.El
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.Pp
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Returns
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.Er ENOMEM
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if sufficient memory is not available for tag creation
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or allocating mapping resources.
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.It Fn bus_dma_tag_destroy "dmat"
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Deallocate the DMA tag
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.Fa dmat
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that was created by
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.Fn bus_dma_tag_create .
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.Pp
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Returns
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.Er EBUSY
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if any DMA maps remain associated with
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.Fa dmat
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or
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.Ql 0
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on success.
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.It Fn bus_dmamap_create "dmat" "flags" "*mapp"
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Allocates and initializes a DMA map.
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Arguments are as follows:
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.Bl -tag -width nsegments -compact
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.It Fa dmat
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DMA tag.
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.It Fa flags
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The value of this argument is currently undefined and should be
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specified as
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.Ql 0 .
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.It Fa mapp
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Pointer to a
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.Vt bus_dmamap_t
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where the resulting DMA map will be stored.
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.El
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.Pp
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Returns
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.Er ENOMEM
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if sufficient memory is not available for creating the
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map or allocating mapping resources.
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.It Fn bus_dmamap_destroy "dmat" "map"
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Frees all resources associated with a given DMA map.
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Arguments are as follows:
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.Bl -tag -width dmat -compact
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.It Fa dmat
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DMA tag used to allocate
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.Fa map .
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.It Fa map
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The DMA map to destroy.
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.El
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.Pp
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Returns
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.Er EBUSY
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if a mapping is still active for
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.Fa map .
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.It Fn bus_dmamap_load "dmat" "map" "buf" "buflen" "*callback" \
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"callback_arg" "flags"
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Creates a mapping in device visible address space of
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.Fa buflen
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|
bytes of
|
|
.Fa buf ,
|
|
associated with the DMA map
|
|
.Fa map.
|
|
Arguments are as follows:
|
|
.Bl -tag -width buflen -compact
|
|
.It Fa dmat
|
|
DMA tag used to allocate
|
|
.Fa map.
|
|
.It Fa map
|
|
A DMA map without a currently active mapping.
|
|
.It Fa buf
|
|
A kernel virtual address pointer to a contiguous (in KVA) buffer, to be
|
|
mapped into device visible address space.
|
|
.It Fa buflen
|
|
The size of the buffer.
|
|
.It Fa callback Fa callback_arg
|
|
The callback function, and its argument.
|
|
.It Fa flags
|
|
The value of this argument is currently undefined, and should be
|
|
specified as
|
|
.Ql 0 .
|
|
.El
|
|
.Pp
|
|
Return values to the caller are as follows:
|
|
.Bl -tag -width EINPROGRESS -compact
|
|
.It 0
|
|
The callback has been called and completed.
|
|
The status of the mapping has been delivered to the callback.
|
|
.It Er EINPROGRESS
|
|
The mapping has been deferred for lack of resources.
|
|
The callback will be called as soon as resources are available.
|
|
Callbacks are serviced in FIFO order.
|
|
To ensure that ordering is guaranteed, all subsequent load requests will also
|
|
be deferred until all callbacks have been processed.
|
|
.It Er EINVAL
|
|
The load request was invalid.
|
|
The callback has not, and will not be called.
|
|
This error value may indicate that
|
|
.Fa dmat ,
|
|
.Fa map ,
|
|
.Fa buf ,
|
|
or
|
|
.Fa callback
|
|
were invalid, or
|
|
.Fa buslen
|
|
was larger than the
|
|
.Fa maxsize
|
|
argument used to create the dma tag
|
|
.Fa dmat .
|
|
.El
|
|
.Pp
|
|
When the callback is called, it is presented with an error value
|
|
indicating the disposition of the mapping.
|
|
Error may be one of the following:
|
|
.Bl -tag -width EINPROGRESS -compact
|
|
.It 0
|
|
The mapping was successful and the
|
|
.Fa dm_segs
|
|
callback argument contains an array of
|
|
.Vt bus_dma_segment_t
|
|
elements describing the mapping.
|
|
This array is only valid during the scope of the callback function.
|
|
.It Er EFBIG
|
|
A mapping could not be achieved within the segment constraints provided
|
|
in the tag even though the requested allocation size was less than maxsize.
|
|
.El
|
|
.It Fn bus_dmamap_load_mbuf "dmat" "map" "mbuf" "callback2" "callback_arg" \
|
|
"flags"
|
|
This is a variation of
|
|
.Fn bus_dmamap_load
|
|
which maps mbuf chains
|
|
for DMA transfers.
|
|
A
|
|
.Vt bus_size_t
|
|
argument is also passed to the callback routine, which
|
|
contains the mbuf chain's packet header length.
|
|
.Pp
|
|
Mbuf chains are assumed to be in kernel virtual address space.
|
|
.Pp
|
|
Returns
|
|
.Er EINVAL
|
|
if the size of the mbuf chain exceeds the maximum limit of the
|
|
DMA tag.
|
|
.It Fn bus_dmamap_load_uio "dmat" "map" "uio" "callback2" "callback_arg" "flags"
|
|
This is a variation of
|
|
.Fn bus_dmamap_load
|
|
which maps buffers pointed to by
|
|
.Fa uio
|
|
for DMA transfers.
|
|
A
|
|
.Vt bus_size_t
|
|
argument is also passed to the callback routine, which contains the size of
|
|
.Fa uio ,
|
|
i.e.
|
|
.Fa uio->uio_resid .
|
|
.Pp
|
|
If
|
|
.Fa uio->uio_segflg
|
|
is
|
|
.Dv UIO_USERSPACE ,
|
|
then it is assumed that the buffer,
|
|
.Fa uio
|
|
is in
|
|
.Fa "uio->uio_td->td_proc" Ns 's
|
|
address space.
|
|
User space memory must be in-core and wired prior to attempting a map
|
|
load operation.
|
|
Pages may be locked using
|
|
.Xr vslock 9 .
|
|
.It Fn bus_dmamap_unload "dmat" "map"
|
|
Unloads a DMA map.
|
|
Arguments are as follows:
|
|
.Bl -tag -width dmam -compact
|
|
.It Fa dmat
|
|
DMA tag used to allocate
|
|
.Fa map .
|
|
.It Fa map
|
|
The DMA map that is to be unloaded.
|
|
.El
|
|
.Pp
|
|
.Fn bus_dmamap_unload
|
|
will not perform any implicit synchronization of DMA buffers.
|
|
This must be done explicitly by a call to
|
|
.Fn bus_dmamap_sync
|
|
prior to unloading the map.
|
|
.It Fn bus_dmamap_sync "dmat" "map" "op"
|
|
Performs synchronization of a device visible mapping with the CPU visible
|
|
memory referenced by that mapping.
|
|
Arguments are as follows:
|
|
.Bl -tag -width dmat -compact
|
|
.It Fa dmat
|
|
DMA tag used to allocate
|
|
.Fa map .
|
|
.It Fa map
|
|
The DMA mapping to be synchronized.
|
|
.It Fa op
|
|
Type of synchronization operation to perform.
|
|
See the definition of
|
|
.Vt bus_dmasync_op_t
|
|
for a description of the acceptable values for
|
|
.Fa op .
|
|
.El
|
|
.Pp
|
|
.Fn bus_dmamap_sync
|
|
is the method used to ensure that CPU and device DMA access to shared
|
|
memory is coherent.
|
|
For example, the CPU might be used to setup the contents of a buffer
|
|
that is to be DMA'ed into a device.
|
|
To ensure that the data are visible via the device's mapping of that
|
|
memory, the buffer must be loaded and a dma sync operation of
|
|
.Dv BUS_DMASYNC_PREREAD
|
|
must be performed.
|
|
Additional sync operations must be performed after every CPU write
|
|
to this memory if additional DMA reads are to be performed.
|
|
Conversely, for the DMA write case, the buffer must be loaded,
|
|
and a dma sync operation of
|
|
.Dv BUS_DMASYNC_PREWRITE
|
|
must be performed.
|
|
The CPU will only be able to see the results of this DMA write
|
|
once the DMA has completed and a
|
|
.Dv BUS_DMASYNC_POSTWRITE
|
|
operation has been performed.
|
|
.Pp
|
|
If DMA read and write operations are not preceded and followed by the
|
|
appropriate synchronization operations, behavior is undefined.
|
|
.It Fn bus_dmamem_alloc "dmat" "**vaddr" "flags" "mapp"
|
|
Allocates memory that is mapped into KVA at the address returned
|
|
in
|
|
.Fa vaddr
|
|
that is permanently loaded into the newly created
|
|
.Vt bus_dmamap_t
|
|
returned via
|
|
.Fa mapp .
|
|
Arguments are as follows:
|
|
.Bl -tag -width alignment -compact
|
|
.It Fa dmat
|
|
DMA tag describing the constraints of the DMA mapping.
|
|
.It Fa vaddr
|
|
Pointer to a pointer that will hold the returned KVA mapping of
|
|
the allocated region.
|
|
.It Fa flags
|
|
Flags are defined as follows:
|
|
.Bl -tag -width BUS_DMA_NOWAIT -compact
|
|
.It Dv BUS_DMA_WAITOK
|
|
The routine can safely wait (sleep) for resources.
|
|
.It Dv BUS_DMA_NOWAIT
|
|
The routine is not allowed to wait for resources.
|
|
If resources are not available,
|
|
.Dv ENOMEM
|
|
is returned.
|
|
.It Dv BUS_DMA_COHERENT
|
|
Attempt to map this memory such that cache sync operations are
|
|
as cheap as possible.
|
|
This flag is typically set on memory that will be accessed by both
|
|
a CPU and a DMA engine, frequently.
|
|
Use of this flag does not remove the requirement of using
|
|
bus_dmamap_sync, but it may reduce the cost of performing
|
|
these operations.
|
|
.It Dv BUS_DMA_ZERO
|
|
Causes the allocated memory to be set to all zeros.
|
|
.El
|
|
.It Fa mapp
|
|
Pointer to storage for the returned DMA map.
|
|
.El
|
|
.Pp
|
|
The size of memory to be allocated is
|
|
.Fa maxsize
|
|
as specified in
|
|
.Fa dmat .
|
|
.Pp
|
|
The current implementation of
|
|
.Fn bus_dmamem_alloc
|
|
will allocate all requests as a single segment.
|
|
.Pp
|
|
Although no explicit loading is required to access the memory
|
|
referenced by the returned map, the synchronization requirements
|
|
as described in the
|
|
.Fn bus_dmamap_sync
|
|
section still apply.
|
|
.Pp
|
|
Returns
|
|
.Er ENOMEM
|
|
if sufficient memory is not available for completing
|
|
the operation.
|
|
.It Fn bus_dmamem_free "dmat" "*vaddr" "map"
|
|
Frees memory previously allocated by
|
|
.Fn bus_dmamem_alloc .
|
|
Any mappings
|
|
will be invalidated.
|
|
Arguments are as follows:
|
|
.Bl -tag -width vaddr -compact
|
|
.It Fa dmat
|
|
DMA tag.
|
|
.It Fa vaddr
|
|
Kernel virtual address of the memory.
|
|
.It Fa map
|
|
DMA map to be invalidated.
|
|
.El
|
|
.El
|
|
.Sh RETURN VALUES
|
|
Behavior is undefined if invalid arguments are passed to
|
|
any of the above functions.
|
|
If sufficient resources cannot be allocated for a given
|
|
transaction,
|
|
.Er ENOMEM
|
|
is returned.
|
|
All
|
|
routines that are not of type,
|
|
.Vt void ,
|
|
will return 0 on success or an error
|
|
code, as discussed above.
|
|
.Pp
|
|
All
|
|
.Vt void
|
|
routines will succeed if provided with valid arguments.
|
|
.Sh SEE ALSO
|
|
.Xr devclass 9 ,
|
|
.Xr device 9 ,
|
|
.Xr driver 9 ,
|
|
.Xr rman 9 ,
|
|
.Xr vslock 9
|
|
.Pp
|
|
.Rs
|
|
.%A "Jason R. Thorpe"
|
|
.%T "A Machine-Independent DMA Framework for NetBSD"
|
|
.%J "Proceedings of the Summer 1998 USENIX Technical Conference"
|
|
.%Q "USENIX Association"
|
|
.%D "June 1998"
|
|
.Re
|
|
.Sh HISTORY
|
|
The
|
|
.Nm
|
|
interface first appeared in
|
|
.Nx 1.3 .
|
|
.Pp
|
|
The
|
|
.Nm
|
|
API was adopted from
|
|
.Nx
|
|
for use in the CAM SCSI subsystem.
|
|
The alterations to the original API were aimed to remove the need for
|
|
a
|
|
.Vt bus_dma_segment_t
|
|
array stored in each
|
|
.Vt bus_dmamap_t
|
|
while allowing callers to queue up on scarce resources.
|
|
.Sh AUTHORS
|
|
The
|
|
.Nm
|
|
interface was designed and implemented by
|
|
.An Jason R. Thorpe
|
|
of the Numerical Aerospace Simulation Facility, NASA Ames Research Center.
|
|
Additional input on the
|
|
.Nm
|
|
design was provided by
|
|
.An -nosplit
|
|
.An Chris Demetriou ,
|
|
.An Charles Hannum ,
|
|
.An Ross Harvey ,
|
|
.An Matthew Jacob ,
|
|
.An Jonathan Stone ,
|
|
and
|
|
.An Matt Thomas .
|
|
.Pp
|
|
The
|
|
.Nm
|
|
interface in
|
|
.Fx
|
|
benefits from the contributions of
|
|
.An Justin T. Gibbs ,
|
|
.An Peter Wemm ,
|
|
.An Doug Rabson ,
|
|
.An Matthew N. Dodd ,
|
|
.An Sam Leffler ,
|
|
.An Maxime Henrion ,
|
|
.An Jake Burkholder ,
|
|
.An Takahashi Yoshihiro ,
|
|
.An Scott Long
|
|
and many others.
|
|
.Pp
|
|
This manual page was written by
|
|
.An Hiten M. Pandya
|
|
and
|
|
.An Justin T. Gibbs .
|