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     bus_dma, bus_dma_tag_create, bus_dma_tag_destroy, bus_dmamap_create, bus_dmamap_destroy,
     bus_dmamap_load, bus_dmamap_load_bio, bus_dmamap_load_ccb, bus_dmamap_load_mbuf,
     bus_dmamap_load_mbuf_sg, bus_dmamap_load_uio, bus_dmamap_unload, bus_dmamap_sync,
     bus_dmamem_alloc, bus_dmamem_free — Bus and Machine Independent DMA Mapping Interface


     #include <machine/bus.h>

     bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment, bus_addr_t boundary,
         bus_addr_t lowaddr, bus_addr_t highaddr, bus_dma_filter_t *filtfunc, void *filtfuncarg,
         bus_size_t maxsize, int nsegments, bus_size_t maxsegsz, int flags,
         bus_dma_lock_t *lockfunc, void *lockfuncarg, bus_dma_tag_t *dmat);

     bus_dma_tag_destroy(bus_dma_tag_t dmat);

     bus_dmamap_create(bus_dma_tag_t dmat, int flags, bus_dmamap_t *mapp);

     bus_dmamap_destroy(bus_dma_tag_t dmat, bus_dmamap_t map);

     bus_dmamap_load(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf, bus_size_t buflen,
         bus_dmamap_callback_t *callback, void *callback_arg, int flags);

     bus_dmamap_load_bio(bus_dma_tag_t dmat, bus_dmamap_t map, struct bio *bio,
         bus_dmamap_callback_t *callback, void *callback_arg, int flags);

     bus_dmamap_load_ccb(bus_dma_tag_t dmat, bus_dmamap_t map, union ccb *ccb,
         bus_dmamap_callback_t *callback, void *callback_arg, int flags);

     bus_dmamap_load_mbuf(bus_dma_tag_t dmat, bus_dmamap_t map, struct mbuf *mbuf,
         bus_dmamap_callback2_t *callback, void *callback_arg, int flags);

     bus_dmamap_load_mbuf_sg(bus_dma_tag_t dmat, bus_dmamap_t map, struct mbuf *mbuf,
         bus_dma_segment_t *segs, int *nsegs, int flags);

     bus_dmamap_load_uio(bus_dma_tag_t dmat, bus_dmamap_t map, struct uio *uio,
         bus_dmamap_callback2_t *callback, void *callback_arg, int flags);

     bus_dmamap_unload(bus_dma_tag_t dmat, bus_dmamap_t map);

     bus_dmamap_sync(bus_dma_tag_t dmat, bus_dmamap_t map, op);

     bus_dmamem_alloc(bus_dma_tag_t dmat, void **vaddr, int flags, bus_dmamap_t *mapp);

     bus_dmamem_free(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map);


     Direct Memory Access (DMA) is a method of transferring data without involving the CPU, thus
     providing higher performance.  A DMA transaction can be achieved between device to memory,
     device to device, or memory to memory.

     The bus_dma API is a bus, device, and machine-independent (MI) interface to DMA mechanisms.
     It provides the client with flexibility and simplicity by abstracting machine dependent
     issues like setting up DMA mappings, handling cache issues, bus specific features and


             A machine-dependent (MD) opaque type that describes the characteristics of DMA
             transactions.  DMA tags are organized into a hierarchy, with each child tag
             inheriting the restrictions of its parent.  This allows all devices along the path
             of DMA transactions to contribute to the constraints of those transactions.

             Client specified address filter having the format:

             int     client_filter(void *filtarg, bus_addr_t testaddr)

             Address filters can be specified during tag creation to allow for devices whose DMA
             address restrictions cannot be specified by a single window.  The filtarg argument
             is specified by the client during tag creation to be passed to all invocations of
             the callback.  The testaddr argument contains a potential starting address of a DMA
             mapping.  The filter function operates on the set of addresses from testaddr to
             ‘trunc_page(testaddr) + PAGE_SIZE - 1’, inclusive.  The filter function should
             return zero if any mapping in this range can be accommodated by the device and non-
             zero otherwise.

             A machine-dependent type that describes individual DMA segments.  It contains the
             following fields:

                     bus_addr_t      ds_addr;
                     bus_size_t      ds_len;

             The ds_addr field contains the device visible address of the DMA segment, and ds_len
             contains the length of the DMA segment.  Although the DMA segments returned by a
             mapping call will adhere to all restrictions necessary for a successful DMA
             operation, some conversion (e.g. a conversion from host byte order to the device's
             byte order) is almost always required when presenting segment information to the

             A machine-dependent opaque type describing an individual mapping.  One map is used
             for each memory allocation that will be loaded.  Maps can be reused once they have
             been unloaded.  Multiple maps can be associated with one DMA tag.  While the value
             of the map may evaluate to NULL on some platforms under certain conditions, it
             should never be assumed that it will be NULL in all cases.

             Client specified callback for receiving mapping information resulting from the load
             of a bus_dmamap_t via bus_dmamap_load(), bus_dmamap_load_bio() or
             bus_dmamap_load_ccb().  Callbacks are of the format:

             void    client_callback(void *callback_arg, bus_dma_segment_t *segs, int nseg, int

             The callback_arg is the callback argument passed to dmamap load functions.  The segs
             and nseg arguments describe an array of bus_dma_segment_t structures that represent
             the mapping.  This array is only valid within the scope of the callback function.
             The success or failure of the mapping is indicated by the error argument.  More
             information on the use of callbacks can be found in the description of the
             individual dmamap load functions.

             Client specified callback for receiving mapping information resulting from the load
             of a bus_dmamap_t via bus_dmamap_load_uio() or bus_dmamap_load_mbuf().

             Callback2s are of the format:

             void    client_callback2(void *callback_arg, bus_dma_segment_t *segs, int nseg,
                     bus_size_t mapsize, int error)

             Callback2's behavior is the same as bus_dmamap_callback_t with the addition that the
             length of the data mapped is provided via mapsize.

             Memory synchronization operation specifier.  Bus DMA requires explicit
             synchronization of memory with its device visible mapping in order to guarantee
             memory coherency.  The bus_dmasync_op_t allows the type of DMA operation that will
             be or has been performed to be communicated to the system so that the correct
             coherency measures are taken.  The operations are represented as bitfield flags that
             can be combined together, though it only makes sense to combine PRE flags or POST
             flags, not both.  See the bus_dmamap_sync() description below for more details on
             how to use these operations.

             All operations specified below are performed from the host memory point of view,
             where a read implies data coming from the device to the host memory, and a write
             implies data going from the host memory to the device.  Alternatively, the
             operations can be thought of in terms of driver operations, where reading a network
             packet or storage sector corresponds to a read operation in bus_dma.

             BUS_DMASYNC_PREREAD    Perform any synchronization required prior to an update of
                                    host memory by the device.

             BUS_DMASYNC_PREWRITE   Perform any synchronization required after an update of host
                                    memory by the CPU and prior to device access to host memory.

             BUS_DMASYNC_POSTREAD   Perform any synchronization required after an update of host
                                    memory by the device and prior to CPU access to host memory.

             BUS_DMASYNC_POSTWRITE  Perform any synchronization required after device access to
                                    host memory.

             Client specified lock/mutex manipulation method.  This will be called from within
             busdma whenever a client lock needs to be manipulated.  In its current form, the
             function will be called immediately before the callback for a DMA load operation
             that has been deferred with BUS_DMA_LOCK and immediately after with BUS_DMA_UNLOCK.
             If the load operation does not need to be deferred, then it will not be called since
             the function loading the map should be holding the appropriate locks.  This method
             is of the format:

             void    lockfunc(void *lockfunc_arg, bus_dma_lock_op_t op)

             The lockfuncarg argument is specified by the client during tag creation to be passed
             to all invocations of the callback.  The op argument specifies the lock operation to

             Two lockfunc implementations are provided for convenience.  busdma_lock_mutex()
             performs standard mutex operations on the sleep mutex provided via lockfuncarg.
             dflt_lock() will generate a system panic if it is called.  It is substituted into
             the tag when lockfunc is passed as NULL to bus_dma_tag_create() and is useful for
             tags that should not be used with deferred load operations.

             Operations to be performed by the client-specified lockfunc().

             BUS_DMA_LOCK    Acquires and/or locks the client locking primitive.

             BUS_DMA_UNLOCK  Releases and/or unlocks the client locking primitive.


     bus_dma_tag_create(parent, alignment, boundary, lowaddr, highaddr, *filtfunc, *filtfuncarg,
             maxsize, nsegments, maxsegsz, flags, lockfunc, lockfuncarg, *dmat)
             Allocates a device specific DMA tag, and initializes it according to the arguments

             parent       Indicates restrictions between the parent bridge, CPU memory, and the
                          device.  Each device must use a master parent tag by calling

             alignment    Alignment constraint, in bytes, of any mappings created using this tag.
                          The alignment must be a power of 2.  Hardware that can DMA starting at
                          any address would specify 1 for byte alignment.  Hardware requiring DMA
                          transfers to start on a multiple of 4K would specify 4096.

             boundary     Boundary constraint, in bytes, of the target DMA memory region.  The
                          boundary indicates the set of addresses, all multiples of the boundary
                          argument, that cannot be crossed by a single bus_dma_segment_t.  The
                          boundary must be a power of 2 and must be no smaller than the maximum
                          segment size.  ‘0’ indicates that there are no boundary restrictions.

             lowaddr, highaddr
                          Bounds of the window of bus address space that cannot be directly
                          accessed by the device.  The window contains all addresses greater than
                          lowaddr and less than or equal to highaddr.  For example, a device
                          incapable of DMA above 4GB, would specify a highaddr of
                          BUS_SPACE_MAXADDR and a lowaddr of BUS_SPACE_MAXADDR_32BIT.  Similarly
                          a device that can only perform DMA to addresses below 16MB would
                          specify a highaddr of BUS_SPACE_MAXADDR and a lowaddr of
                          BUS_SPACE_MAXADDR_24BIT.  Some implementations requires that some
                          region of device visible address space, overlapping available host
                          memory, be outside the window.  This area of ‘safe memory’ is used to
                          bounce requests that would otherwise conflict with the exclusion

             filtfunc     Optional filter function (may be NULL) to be called for any attempt to
                          map memory into the window described by lowaddr and highaddr.  A filter
                          function is only required when the single window described by lowaddr
                          and highaddr cannot adequately describe the constraints of the device.
                          The filter function will be called for every machine page that overlaps
                          the exclusion window.

             filtfuncarg  Argument passed to all calls to the filter function for this tag.  May
                          be NULL.

             maxsize      Maximum size, in bytes, of the sum of all segment lengths in a given
                          DMA mapping associated with this tag.

             nsegments    Number of discontinuities (scatter/gather segments) allowed in a DMA
                          mapped region.  If there is no restriction, BUS_SPACE_UNRESTRICTED may
                          be specified.

             maxsegsz     Maximum size, in bytes, of a segment in any DMA mapped region
                          associated with dmat.

             flags        Are as follows:

                          BUS_DMA_ALLOCNOW  Pre-allocate enough resources to handle at least one
                                            map load operation on this tag.  If sufficient
                                            resources are not available, ENOMEM is returned.
                                            This should not be used for tags that only describe
                                            buffers that will be allocated with
                                            bus_dmamem_alloc().  Also, due to resource sharing
                                            with other tags, this flag does not guarantee that
                                            resources will be allocated or reserved exclusively
                                            for this tag.  It should be treated only as a minor

             lockfunc     Optional lock manipulation function (may be NULL) to be called when
                          busdma needs to manipulate a lock on behalf of the client.  If NULL is
                          specified, dflt_lock() is used.

             lockfuncarg  Optional argument to be passed to the function specified by lockfunc.

             dmat         Pointer to a bus_dma_tag_t where the resulting DMA tag will be stored.

             Returns ENOMEM if sufficient memory is not available for tag creation or allocating
             mapping resources.

             Deallocate the DMA tag dmat that was created by bus_dma_tag_create().

             Returns EBUSY if any DMA maps remain associated with dmat or ‘0’ on success.

     bus_dmamap_create(dmat, flags, *mapp)
             Allocates and initializes a DMA map.  Arguments are as follows:

             dmat       DMA tag.

             flags      Are as follows:

                        BUS_DMA_COHERENT  Attempt to map the memory loaded with this map such
                                          that cache sync operations are as cheap as possible.
                                          This flag is typically set on maps when the memory
                                          loaded with these will be accessed by both a CPU and a
                                          DMA engine, frequently such as control data and as
                                          opposed to streamable data such as receive and transmit
                                          buffers.  Use of this flag does not remove the
                                          requirement of using bus_dmamap_sync(), but it may
                                          reduce the cost of performing these operations.  For
                                          bus_dmamap_create(), the BUS_DMA_COHERENT flag is
                                          currently implemented on sparc64.

             mapp       Pointer to a bus_dmamap_t where the resulting DMA map will be stored.

             Returns ENOMEM if sufficient memory is not available for creating the map or
             allocating mapping resources.

     bus_dmamap_destroy(dmat, map)
             Frees all resources associated with a given DMA map.  Arguments are as follows:

             dmat  DMA tag used to allocate map.

             map   The DMA map to destroy.

             Returns EBUSY if a mapping is still active for map.

     bus_dmamap_load(dmat, map, buf, buflen, *callback, callback_arg, flags)
             Creates a mapping in device visible address space of buflen bytes of buf, associated
             with the DMA map map.  This call will always return immediately and will not block
             for any reason.  Arguments are as follows:

             dmat    DMA tag used to allocate map.

             map     A DMA map without a currently active mapping.

             buf     A kernel virtual address pointer to a contiguous (in KVA) buffer, to be
                     mapped into device visible address space.

             buflen  The size of the buffer.

             callback callback_arg
                     The callback function, and its argument.  This function is called once
                     sufficient mapping resources are available for the DMA operation.  If
                     resources are temporarily unavailable, this function will be deferred until
                     later, but the load operation will still return immediately to the caller.
                     Thus, callers should not assume that the callback will be called before the
                     load returns, and code should be structured appropriately to handle this.
                     See below for specific flags and error codes that control this behavior.

             flags   Are as follows:

                     BUS_DMA_NOWAIT  The load should not be deferred in case of insufficient
                                     mapping resources, and instead should return immediately
                                     with an appropriate error.

                                     The generated transactions to and from the virtual page are
                                     non-cacheable.  For bus_dmamap_load(), the BUS_DMA_NOCACHE
                                     flag is currently implemented on sparc64.

             Return values to the caller are as follows:

             0            The callback has been called and completed.  The status of the mapping
                          has been delivered to the callback.

             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.

                          Note that subsequent load operations for the same tag that do not
                          require extra resources will still succeed.  This may result in out-of-
                          order processing of requests.  If the caller requires the order of
                          requests to be preserved, then the caller is required to stall
                          subsequent requests until a pending request's callback is invoked.

             ENOMEM       The load request has failed due to insufficient resources, and the
                          caller specifically used the BUS_DMA_NOWAIT flag.

             EINVAL       The load request was invalid.  The callback has been called and has
                          been provided the same error.  This error value may indicate that dmat,
                          map, buf, or callback were invalid, or buflen was larger than the
                          maxsize argument used to create the dma tag dmat.

             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:

             0            The mapping was successful and the dm_segs callback argument contains
                          an array of bus_dma_segment_t elements describing the mapping.  This
                          array is only valid during the scope of the callback function.

             EFBIG        A mapping could not be achieved within the segment constraints provided
                          in the tag even though the requested allocation size was less than

     bus_dmamap_load_bio(dmat, map, bio, callback, callback_arg, flags)
             This is a variation of bus_dmamap_load() which maps buffers pointed to by bio for
             DMA transfers.  bio may point to either a mapped or unmapped buffer.

     bus_dmamap_load_ccb(dmat, map, ccb, callback, callback_arg, flags)
             This is a variation of bus_dmamap_load() which maps data pointed to by ccb for DMA
             transfers.  The data for ccb may be any of the following types:

             CAM_DATA_VADDR     The data is a single KVA buffer.

             CAM_DATA_PADDR     The data is a single bus address range.

             CAM_DATA_SG        The data is a scatter/gather list of KVA buffers.

             CAM_DATA_SG_PADDR  The data is a scatter/gather list of bus address ranges.

             CAM_DATA_BIO       The data is contained in a struct bio attached to the CCB.

             bus_dmamap_load_ccb() supports the following CCB XPT function codes:


     bus_dmamap_load_mbuf(dmat, map, mbuf, callback2, callback_arg, flags)
             This is a variation of bus_dmamap_load() which maps mbuf chains for DMA transfers.
             A bus_size_t argument is also passed to the callback routine, which contains the
             mbuf chain's packet header length.  The BUS_DMA_NOWAIT flag is implied, thus no
             callback deferral will happen.

             Mbuf chains are assumed to be in kernel virtual address space.

             Beside the error values listed for bus_dmamap_load(), EINVAL will be returned if the
             size of the mbuf chain exceeds the maximum limit of the DMA tag.

     bus_dmamap_load_mbuf_sg(dmat, map, mbuf, segs, nsegs, flags)
             This is just like bus_dmamap_load_mbuf() except that it returns immediately without
             calling a callback function.  It is provided for efficiency.  The scatter/gather
             segment array segs is provided by the caller and filled in directly by the function.
             The nsegs argument is returned with the number of segments filled in.  Returns the
             same errors as bus_dmamap_load_mbuf().

     bus_dmamap_load_uio(dmat, map, uio, callback2, callback_arg, flags)
             This is a variation of bus_dmamap_load() which maps buffers pointed to by uio for
             DMA transfers.  A bus_size_t argument is also passed to the callback routine, which
             contains the size of uio, i.e.  uio->uio_resid.  The BUS_DMA_NOWAIT flag is implied,
             thus no callback deferral will happen.  Returns the same errors as

             If uio->uio_segflg is UIO_USERSPACE, then it is assumed that the buffer, uio is in
             uio->uio_td->td_proc's address space.  User space memory must be in-core and wired
             prior to attempting a map load operation.  Pages may be locked using vslock(9).

     bus_dmamap_unload(dmat, map)
             Unloads a DMA map.  Arguments are as follows:

             dmat  DMA tag used to allocate map.

             map   The DMA map that is to be unloaded.

             bus_dmamap_unload() will not perform any implicit synchronization of DMA buffers.
             This must be done explicitly by a call to bus_dmamap_sync() prior to unloading the

     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:

             dmat  DMA tag used to allocate map.

             map   The DMA mapping to be synchronized.

             op    Type of synchronization operation to perform.  See the definition of
                   bus_dmasync_op_t for a description of the acceptable values for op.

             The bus_dmamap_sync() function is the method used to ensure that CPU's and device's
             direct memory access (DMA) to shared memory is coherent.  For example, the CPU might
             be used to set up the contents of a buffer that is to be made available to 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 BUS_DMASYNC_PREWRITE must be
             performed after the CPU has updated the buffer and before the device access is
             initiated.  If the CPU modifies this buffer again later, another
             BUS_DMASYNC_PREWRITE sync operation must be performed before an additional device
             access.  Conversely, suppose a device updates memory that is to be read by a CPU.
             In this case, the buffer must be loaded, and a DMA sync operation of
             BUS_DMASYNC_PREREAD must be performed before the device access is initiated.  The
             CPU will only be able to see the results of this memory update once the DMA
             operation has completed and a BUS_DMASYNC_POSTREAD sync operation has been

             If read and write operations are not preceded and followed by the appropriate
             synchronization operations, behavior is undefined.

     bus_dmamem_alloc(dmat, **vaddr, flags, *mapp)
             Allocates memory that is mapped into KVA at the address returned in vaddr and that
             is permanently loaded into the newly created bus_dmamap_t returned via mapp.
             Arguments are as follows:

             dmat       DMA tag describing the constraints of the DMA mapping.

             vaddr      Pointer to a pointer that will hold the returned KVA mapping of the
                        allocated region.

             flags      Flags are defined as follows:

                        BUS_DMA_WAITOK  The routine can safely wait (sleep) for resources.

                        BUS_DMA_NOWAIT  The routine is not allowed to wait for resources.  If
                                        resources are not available, ENOMEM is returned.

                                        Attempt to map this memory in a coherent fashion.  See
                                        bus_dmamap_create() above for a description of this flag.
                                        For bus_dmamem_alloc(), the BUS_DMA_COHERENT flag is
                                        currently implemented on arm and sparc64.

                        BUS_DMA_ZERO    Causes the allocated memory to be set to all zeros.

                                        The allocated memory will not be cached in the processor
                                        caches.  All memory accesses appear on the bus and are
                                        executed without reordering.  For bus_dmamem_alloc(), the
                                        BUS_DMA_NOCACHE flag is currently implemented on amd64
                                        and i386 where it results in the Strong Uncacheable PAT
                                        to be set for the allocated virtual address range.

             mapp       Pointer to a bus_dmamap_t where the resulting DMA map will be stored.

             The size of memory to be allocated is maxsize as specified in the call to
             bus_dma_tag_create() for dmat.

             The current implementation of bus_dmamem_alloc() will allocate all requests as a
             single segment.

             An initial load operation is required to obtain the bus address of the allocated
             memory, and an unload operation is required before freeing the memory, as described
             below in bus_dmamem_free().  Maps are automatically handled by this function and
             should not be explicitly allocated or destroyed.

             Although an explicit load is not required for each access to the memory referenced
             by the returned map, the synchronization requirements as described in the
             bus_dmamap_sync() section still apply and should be used to achieve portability on
             architectures without coherent buses.

             Returns ENOMEM if sufficient memory is not available for completing the operation.

     bus_dmamem_free(dmat, *vaddr, map)
             Frees memory previously allocated by bus_dmamem_alloc().  Any mappings will be
             invalidated.  Arguments are as follows:

             dmat   DMA tag.

             vaddr  Kernel virtual address of the memory.

             map    DMA map to be invalidated.


     Behavior is undefined if invalid arguments are passed to any of the above functions.  If
     sufficient resources cannot be allocated for a given transaction, ENOMEM is returned.  All
     routines that are not of type void will return 0 on success or an error code on failure as
     discussed above.

     All void routines will succeed if provided with valid arguments.


     Two locking protocols are used by bus_dma.  The first is a private global lock that is used
     to synchronize access to the bounce buffer pool on the architectures that make use of them.
     This lock is strictly a leaf lock that is only used internally to bus_dma and is not exposed
     to clients of the API.

     The second protocol involves protecting various resources stored in the tag.  Since almost
     all bus_dma operations are done through requests from the driver that created the tag, the
     most efficient way to protect the tag resources is through the lock that the driver uses.
     In cases where bus_dma acts on its own without being called by the driver, the lock
     primitive specified in the tag is acquired and released automatically.  An example of this
     is when the bus_dmamap_load() callback function is called from a deferred context instead of
     the driver context.  This means that certain bus_dma functions must always be called with
     the same lock held that is specified in the tag.  These functions include:


     There is one exception to this rule.  It is common practice to call some of these functions
     during driver start-up without any locks held.  So long as there is a guarantee of no
     possible concurrent use of the tag by different threads during this operation, it is safe to
     not hold a lock for these functions.

     Certain bus_dma operations should not be called with the driver lock held, either because
     they are already protected by an internal lock, or because they might sleep due to memory or
     resource allocation.  The following functions must not be called with any non-sleepable
     locks held:


     All other functions do not have a locking protocol and can thus be called with or without
     any system or driver locks held.


     devclass(9), device(9), driver(9), rman(9), vslock(9)

     Jason R. Thorpe, "A Machine-Independent DMA Framework for NetBSD", Proceedings of the Summer
     1998 USENIX Technical Conference, USENIX Association, June 1998.


     The bus_dma interface first appeared in NetBSD 1.3.

     The bus_dma API was adopted from NetBSD for use in the CAM SCSI subsystem.  The alterations
     to the original API were aimed to remove the need for a bus_dma_segment_t array stored in
     each bus_dmamap_t while allowing callers to queue up on scarce resources.


     The bus_dma interface was designed and implemented by Jason R. Thorpe of the Numerical
     Aerospace Simulation Facility, NASA Ames Research Center.  Additional input on the bus_dma
     design was provided by Chris Demetriou, Charles Hannum, Ross Harvey, Matthew Jacob, Jonathan
     Stone, and Matt Thomas.

     The bus_dma interface in FreeBSD benefits from the contributions of Justin T. Gibbs, Peter
     Wemm, Doug Rabson, Matthew N. Dodd, Sam Leffler, Maxime Henrion, Jake Burkholder, Takahashi
     Yoshihiro, Scott Long and many others.

     This manual page was written by Hiten M. Pandya and Justin T. Gibbs.