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when it won't be called. The old wording was correct, but not sufficiently specific to understand when and how it would be called. The new wording describes the current implementation's usage (which should be updated if other appropriate times are decided upon), specifically that it is called only when the load operation is deferred to keep the locking state consistent. When the operation isn't deferred, the calling routine is assumed to have a coherent locking world. Reviewed by: scottl
797 lines
24 KiB
Groff
797 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
|
|
Argument passed to all calls to the filter function for this tag.
|
|
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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|
Allocate the resources necessary to guarantee that all map load
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operations associated with this tag will not block.
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If sufficient resources are not available,
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|
.Er ENOMEM
|
|
is returned.
|
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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.
|
|
If NULL is specified,
|
|
.Fn dflt_lock
|
|
is used.
|
|
.It Fa lockfuncarg
|
|
Optional argument to be passed to the function specified by
|
|
.Fa lockfunc .
|
|
.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.
|
|
.El
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.Pp
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|
Returns
|
|
.Er ENOMEM
|
|
if sufficient memory is not available for tag creation
|
|
or allocating mapping resources.
|
|
.It Fn bus_dma_tag_destroy "dmat"
|
|
Deallocate the DMA tag
|
|
.Fa dmat
|
|
that was created by
|
|
.Fn bus_dma_tag_create .
|
|
.Pp
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|
Returns
|
|
.Er EBUSY
|
|
if any DMA maps remain associated with
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|
.Fa dmat
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|
or
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|
.Ql 0
|
|
on success.
|
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.It Fn bus_dmamap_create "dmat" "flags" "*mapp"
|
|
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
|
|
specified as
|
|
.Ql 0 .
|
|
.It Fa mapp
|
|
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
|
|
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"
|
|
Frees all resources associated with a given DMA map.
|
|
Arguments are as follows:
|
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.Bl -tag -width dmat -compact
|
|
.It Fa dmat
|
|
DMA tag used to allocate
|
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.Fa map .
|
|
.It Fa map
|
|
The DMA map to destroy.
|
|
.El
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|
.Pp
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|
Returns
|
|
.Er EBUSY
|
|
if a mapping is still active for
|
|
.Fa map .
|
|
.It Fn bus_dmamap_load "dmat" "map" "buf" "buflen" "*callback" \
|
|
"callback_arg" "flags"
|
|
Creates a mapping in device visible address space of
|
|
.Fa buflen
|
|
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.
|
|
DMA maps created from DMA tags that are allocated with
|
|
the
|
|
.Dv BUS_DMA_ALLOCNOW
|
|
flag will never return this status for a load operation.
|
|
.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.
|
|
.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
|
|
.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 .
|