BUS_DMA(9)             NetBSD Kernel Developer's Manual             BUS_DMA(9)

NAME
     bus_dma, bus_dmamap_create, bus_dmamap_destroy, bus_dmamap_load,
     bus_dmamap_load_mbuf, bus_dmamap_load_uio, bus_dmamap_load_raw,
     bus_dmamap_unload, bus_dmamap_sync, bus_dmamem_alloc, bus_dmamem_free,
     bus_dmamem_map, bus_dmamem_unmap, bus_dmamem_mmap, bus_dmatag_subregion,
     bus_dmatag_destroy -- Bus and Machine Independent DMA Mapping Interface

SYNOPSIS
     #include <machine/bus.h>

     int
     bus_dmamap_create(bus_dma_tag_t tag, bus_size_t size, int nsegments,
         bus_size_t maxsegsz, bus_size_t boundary, int flags,
         bus_dmamap_t *dmamp);

     void
     bus_dmamap_destroy(bus_dma_tag_t tag, bus_dmamap_t dmam);

     int
     bus_dmamap_load(bus_dma_tag_t tag, bus_dmamap_t dmam, void *buf,
         bus_size_t buflen, struct lwp *l, int flags);

     int
     bus_dmamap_load_mbuf(bus_dma_tag_t tag, bus_dmamap_t dmam,
         struct mbuf *chain, int flags);

     int
     bus_dmamap_load_uio(bus_dma_tag_t tag, bus_dmamap_t dmam,
         struct uio *uio, int flags);

     int
     bus_dmamap_load_raw(bus_dma_tag_t tag, bus_dmamap_t dmam,
         bus_dma_segment_t *segs, int nsegs, bus_size_t size, int flags);

     void
     bus_dmamap_unload(bus_dma_tag_t tag, bus_dmamap_t dmam);

     void
     bus_dmamap_sync(bus_dma_tag_t tag, bus_dmamap_t dmam, bus_addr_t offset,
         bus_size_t len, int ops);

     int
     bus_dmamem_alloc(bus_dma_tag_t tag, bus_size_t size,
         bus_size_t alignment, bus_size_t boundary, bus_dma_segment_t *segs,
         int nsegs, int *rsegs, int flags);

     void
     bus_dmamem_free(bus_dma_tag_t tag, bus_dma_segment_t *segs, int nsegs);

     int
     bus_dmamem_map(bus_dma_tag_t tag, bus_dma_segment_t *segs, int nsegs,
         size_t size, void **kvap, int flags);

     void
     bus_dmamem_unmap(bus_dma_tag_t tag, void *kva, size_t size);

     paddr_t
     bus_dmamem_mmap(bus_dma_tag_t tag, bus_dma_segment_t *segs, int nsegs,
         off_t off, int prot, int flags);

     int
     bus_dmatag_subregion(bus_dma_tag_t tag, bus_addr_t min_addr,
         bus_addr_t max_addr, bus_dma_tag_t *newtag, int flags);

     void
     bus_dmatag_destroy(bus_dma_tag_t tag);

DESCRIPTION
     Provide a bus- and machine-independent "DMA mapping interface."

NOTES
     All data structures, function prototypes, and macros will be defined by
     the port-specific header <machine/bus.h>.  Note that this document
     assumes the existence of types already defined by the current "bus.h"
     interface.

     Unless otherwise noted, all function calls in this interface may be
     defined as cpp(1) macros.

DATA TYPES
     Individual implementations may name these structures whatever they wish,
     providing that the external representations are:

     bus_dma_tag_t
              A machine-dependent opaque type describing the implementation of
              DMA for a given bus.

     bus_dma_segment_t
              A structure with at least the following members:

                      bus_addr_t      ds_addr;
                      bus_size_t      ds_len;

              The structure may have machine-dependent members and arbitrary
              layout.  The values in ds_addr and ds_len are suitable for pro-
              gramming into DMA controller address and length registers.

     bus_dmamap_t
              A pointer to a structure with at least the following members:

                      bus_size_t      dm_maxsegsz;
                      bus_size_t      dm_mapsize;
                      int             dm_nsegs;
                      bus_dma_segment_t *dm_segs;

              The structure may have machine-dependent members and arbitrary
              layout.  The dm_maxsegsz member indicates the maximum number of
              bytes that may be transferred by any given DMA segment.  The
              dm_mapsize member indicates the size of the mapping.  A value of
              0 indicates the mapping is invalid.  The dm_segs member may be
              an array of segments or a pointer to an array of segments.  The
              dm_nsegs member indicates the number of segments in dm_segs.

FUNCTIONS
     bus_dmamap_create(tag, size, nsegments, maxsegsz, boundary, flags, dmamp)
              Allocates a DMA handle and initializes it according to the
              parameters provided.  Arguments are as follows:
              tag        This is the bus_dma_tag_t passed down from the parent
                         driver via <bus>_attach_args.
              size       This is the maximum DMA transfer that can be mapped
                         by the handle.
              nsegments  Number of segments the device can support in a single
                         DMA transaction.  This may be the number of scatter-
                         gather descriptors supported by the device.
              maxsegsz   The maximum number of bytes that may be transferred
                         by any given DMA segment and will be assigned to the
                         dm_maxsegsz member.
              boundary   Some DMA controllers are not able to transfer data
                         that crosses a particular boundary.  This argument
                         allows this boundary to be specified.  The boundary
                         lines begin at 0, and occur every boundary bytes.
                         Mappings may begin on a boundary line but may not end
                         on or cross a boundary line.  If no boundary condi-
                         tion needs to be observed, a boundary argument of 0
                         should be used.
              flags      Flags are defined as follows:
                         BUS_DMA_WAITOK    It is safe to wait (sleep) for
                                           resources during this call.
                         BUS_DMA_NOWAIT    It is not safe to wait (sleep) for
                                           resources during this call.
                         BUS_DMA_ALLOCNOW  Perform any resource allocation
                                           this handle may need now.  If this
                                           is not specified, the allocation
                                           may be deferred to
                                           bus_dmamap_load().  If this flag is
                                           specified, bus_dmamap_load() will
                                           not block on resource allocation.
                         BUS_DMA_BUS[1-4]  These flags are placeholders, and
                                           may be used by busses to provide
                                           bus-dependent functionality.
              dmamp      This is a pointer to a bus_dmamap_t.  A DMA map will
                         be allocated and pointed to by dmamp upon successful
                         completion of this routine.  dmamp is undefined if
                         this routine fails.

              Behavior is not defined if invalid arguments are passed to
              bus_dmamap_create().

              Returns 0 on success, or an error code to indicate mode of fail-
              ure.

     bus_dmamap_destroy(tag, dmam)
              Frees all resources associated with a given DMA handle.  Argu-
              ments are as follows:
              tag   This is the bus_dma_tag_t passed down from the parent
                    driver via <bus>_attach_args.
              dmam  The DMA handle to destroy.

              In the event that the DMA handle contains a valid mapping, the
              mapping will be unloaded via the same mechanism used by
              bus_dmamap_unload().

              Behavior is not defined if invalid arguments are passed to
              bus_dmamap_destroy().

              If given valid arguments, bus_dmamap_destroy() always succeeds.

     bus_dmamap_load(tag, dmam, buf, buflen, l, flags)
              Loads a DMA handle with mappings for a DMA transfer.  It assumes
              that all pages involved in a DMA transfer are wired.  Arguments
              are as follows:
              tag     This is the bus_dma_tag_t passed down from the parent
                      driver via <bus>_attach_args.
              dmam    The DMA handle with which to map the transfer.
              buf     The buffer to be used for the DMA transfer.
              buflen  The size of the buffer.
              l       Used to indicate the address space in which the buffer
                      is located.  If NULL, the buffer is assumed to be in
                      kernel space.  Otherwise, the buffer is assumed to be in
                      lwp l's address space.
              flags   are defined as follows:
                      BUS_DMA_WAITOK     It is safe to wait (sleep) for
                                         resources during this call.
                      BUS_DMA_NOWAIT     It is not safe to wait (sleep) for
                                         resources during this call.
                      BUS_DMA_STREAMING  By default, the bus_dma API assumes
                                         that there is coherency between mem-
                                         ory and the device performing the DMA
                                         transaction.  Some platforms, how-
                                         ever, have special hardware, such as
                                         an ``I/O cache'', which may improve
                                         performance of some types of DMA
                                         transactions, but which break the
                                         assumption that there is coherency
                                         between memory and the device per-
                                         forming the DMA transaction.  This
                                         flag allows the use of this special
                                         hardware, provided that the device is
                                         doing sequential, unidirectional
                                         transfers which conform to certain
                                         alignment and size constraints
                                         defined by the platform.  If the
                                         platform does not support the fea-
                                         ture, or if the buffer being loaded
                                         into the DMA map does not conform to
                                         the constraints required for use of
                                         the feature, then this flag will be
                                         silently ignored.  Also refer to the
                                         use of this flag with the
                                         bus_dmamem_alloc() function.
                      BUS_DMA_READ       This is a hint to the machine-depen-
                                         dent back-end that indicates the map-
                                         ping will be used only for a device
                                         -> memory transaction.  The back-end
                                         may perform optimizations based on
                                         this information.
                      BUS_DMA_WRITE      This is a hint to the machine-depen-
                                         dent back-end that indicates the map-
                                         ping will be used only for a memory
                                         -> device transaction.  The back-end
                                         may perform optimizations based on
                                         this information.
                      BUS_DMA_BUS[1-4]   These flags are placeholders, and may
                                         be used by busses to provide bus-
                                         dependent functionality.

              As noted above, if a DMA handle is created with
              BUS_DMA_ALLOCNOW, bus_dmamap_load() will never block.

              If a call to bus_dmamap_load() fails, the mapping in the DMA
              handle will be invalid.  It is the responsibility of the caller
              to clean up any inconsistent device state resulting from incom-
              plete iteration through the uio.

              Behavior is not defined if invalid arguments are passed to
              bus_dmamap_load().

              Returns 0 on success, or an error code to indicate mode of fail-
              ure.

     bus_dmamap_load_mbuf(tag, dmam, chain, flags)
              This is a variation of bus_dmamap_load() which maps mbuf chains
              for DMA transfers.  Mbuf chains are assumed to be in kernel vir-
              tual address space.

     bus_dmamap_load_uio(tag, dmam, uio, flags)
              This is a variation of bus_dmamap_load() which maps buffers
              pointed to by uio for DMA transfers.  Determination if the
              buffers are in user or kernel virtual address space is done
              internally, according to uio->uio_vmspace.  See uiomove(9) for
              details of the uio structure.

     bus_dmamap_load_raw(tag, dmam, segs, nsegs, size, flags)
              This is a variation of bus_dmamap_load() which maps buffers
              allocated by bus_dmamem_alloc() (see below).  The segs argument
              is an array of bus_dma_segment_t's filled in by
              bus_dmamem_alloc().  The nsegs argument is the number of seg-
              ments in the array.  The size argument is the size of the DMA
              transfer.

     bus_dmamap_unload(tag, dmam)
              Deletes the mappings for a given DMA handle.  Arguments are as
              follows:
              tag   This is the bus_dma_tag_t passed down from the parent
                    driver via <bus>_attach_args.
              dmam  The DMA handle containing the mappings which are to be
                    deleted.

              If the DMA handle was created with BUS_DMA_ALLOCNOW,
              bus_dmamap_unload() will not free the corresponding resources
              which were allocated by bus_dmamap_create().  This is to ensure
              that bus_dmamap_load() will never block on resources if the han-
              dle was created with BUS_DMA_ALLOCNOW.

              bus_dmamap_unload() will not perform any implicit synchroniza-
              tion of DMA buffers.  This must be done explicitly by
              bus_dmamap_sync().

              bus_dmamap_unload() will restore the dm_maxsegsz member to its
              initial value assigned by bus_dmamap_create().

              Behavior is not defined if invalid arguments are passed to
              bus_dmamap_unload().

              If given valid arguments, bus_dmamap_unload() always succeeds.

     bus_dmamap_sync(tag, dmam, offset, len, ops)
              Performs pre- and post-DMA operation cache and/or buffer syn-
              chronization.  Arguments are as follows:
              tag     This is the bus_dma_tag_t passed down from the parent
                      driver via <bus>_attach_args.
              dmam    The DMA mapping to be synchronized.
              offset  The offset into the DMA mapping to synchronize.
              len     The length of the mapping from offset to synchronize.
              ops     One or more synchronization operation to perform.  The
                      following DMA synchronization operations are defined:
                      BUS_DMASYNC_PREREAD    Perform any pre-read DMA cache
                                             and/or bounce operations.
                      BUS_DMASYNC_POSTREAD   Perform any post-read DMA cache
                                             and/or bounce operations.
                      BUS_DMASYNC_PREWRITE   Perform any pre-write DMA cache
                                             and/or bounce operations.
                      BUS_DMASYNC_POSTWRITE  Perform any post-write DMA cache
                                             and/or bounce operations.

                      More than one operation may performed in a given syn-
                      chronization call.  Mixing of PRE and POST operations is
                      not allowed, and behavior is undefined if this is
                      attempted.

              Synchronization operations are expressed from the perspective of
              the host RAM, e.g., a device -> memory operation is a READ and a
              memory -> device operation is a WRITE.

              bus_dmamap_sync() may consult state kept within the DMA map to
              determine if the memory is mapped in a DMA coherent fashion.  If
              so, bus_dmamap_sync() may elect to skip certain expensive opera-
              tions, such as flushing of the data cache.  See bus_dmamem_map()
              for more information on this subject.

              On platforms which implement a weak memory access ordering
              model, bus_dmamap_sync() will always cause the appropriate mem-
              ory barriers to be issued.

              This function exists to ensure that the host and the device have
              a consistent view of a range of DMA memory, before and after a
              DMA operation.

              An example of using bus_dmamap_sync(), involving multiple read-
              write use of a single mapping might look like this:

              bus_dmamap_load(...);

              while (not done) {
                      /* invalidate soon-to-be-stale cache blocks */
                      bus_dmamap_sync(..., BUS_DMASYNC_PREREAD);

                      [ do read DMA ]

                      /* copy from bounce */
                      bus_dmamap_sync(..., BUS_DMASYNC_POSTREAD);

                      /* read data now in driver-provided buffer */

                      [ computation ]

                      /* data to be written now in driver-provided buffer */

                      /* flush write buffers and writeback, copy to bounce */
                      bus_dmamap_sync(..., BUS_DMASYNC_PREWRITE);

                      [ do write DMA ]

                      /* probably a no-op, but provided for consistency */
                      bus_dmamap_sync(..., BUS_DMASYNC_POSTWRITE);
              }

              bus_dmamap_unload(...);

              This function must be called to synchronize DMA buffers before
              and after a DMA operation.  Other bus_dma functions can not be
              relied on to do this synchronization implicitly.  If DMA read
              and write operations are not preceded and followed by the appro-
              priate synchronization operations, behavior is undefined.

              Behavior is not defined if invalid arguments are passed to
              bus_dmamap_sync().

              If given valid arguments, bus_dmamap_sync() always succeeds.

     bus_dmamem_alloc(tag, size, alignment, boundary, segs, ...)
              Allocates memory that is "DMA safe" for the bus corresponding to
              the given tag.

              The mapping of this memory is machine-dependent (or "opaque");
              machine-independent code is not to assume that the addresses
              returned are valid in kernel virtual address space, or that the
              addresses returned are system physical addresses.  The address
              value returned as part of segs can thus not be used to program
              DMA controller address registers.  Only the values in the
              dm_segs array of a successfully loaded DMA map (using
              bus_dmamap_load()) can be used for this purpose.

              Allocations will always be rounded to the hardware page size.
              Callers may wish to take advantage of this, and cluster alloca-
              tion of small data structures.  Arguments are as follows:
              tag        This is the bus_dma_tag_t passed down from the parent
                         driver via <bus>_attach_args.
              size       The amount of memory to allocate.
              alignment  Each segment in the allocated memory will be aligned
                         to this value.  If the alignment is less than a hard-
                         ware page size, it will be rounded up to the hardware
                         page size.  This value must be a power of two.
              boundary   Each segment in the allocated memory must not cross
                         this boundary (relative to zero).  This value must be
                         a power of two.  A boundary value less than the size
                         of the allocation is invalid.
              segs       An array of bus_dma_segment_t's, filled in as memory
                         is allocated, representing the opaque addresses of
                         the memory chunks.
              nsegs      Specifies the number of segments in segs, and this is
                         the maximum number of segments that the allocated
                         memory may contain.
              rsegs      Used to return the actual number of segments the mem-
                         ory contains.
              flags      Flags are defined as follows:
                         BUS_DMA_WAITOK     It is safe to wait (sleep) for
                                            resources during this call.
                         BUS_DMA_NOWAIT     It is not safe to wait (sleep) for
                                            resources during this call.
                         BUS_DMA_STREAMING  Adjusts, if necessary, the size,
                                            alignment, and boundary constrains
                                            to conform to the platform-depen-
                                            dent requirements for the use of
                                            the BUS_DMA_STREAMING flag with
                                            the bus_dmamap_load() function.
                                            If the platform does not support
                                            the BUS_DMA_STREAMING feature, or
                                            if the size, alignment, and bound-
                                            ary constraints would already sat-
                                            isfy the platform's requirements,
                                            this flag is silently ignored.
                                            The BUS_DMA_STREAMING flag will
                                            never relax the constraints speci-
                                            fied in the call.
                         BUS_DMA_BUS[1-4]   These flags are placeholders, and
                                            may be used by busses to provide
                                            bus-dependent functionality.

              All pages allocated by bus_dmamem_alloc() will be wired down
              until they are freed by bus_dmamem_free().

              Behavior is undefined if invalid arguments are passed to
              bus_dmamem_alloc().

              Returns 0 on success, or an error code indicating mode of fail-
              ure.

     bus_dmamem_free(tag, segs, nsegs)
              Frees memory previously allocated by bus_dmamem_alloc().  Any
              mappings will be invalidated.  Arguments are as follows:
              tag    This is the bus_dma_tag_t passed down from the parent
                     driver via <bus>_attach_args.
              segs   The array of bus_dma_segment_t's filled in by
                     bus_dmamem_alloc().
              nsegs  The number of segments in segs.

              Behavior is undefined if invalid arguments are passed to
              bus_dmamem_free().

              If given valid arguments, bus_dmamem_free() always succeeds.

     bus_dmamem_map(tag, segs, nsegs, size, kvap, flags)
              Maps memory allocated with bus_dmamem_alloc() into kernel vir-
              tual address space.  Arguments are as follows:
              tag    This is the bus_dma_tag_t passed down from the parent
                     driver via <bus>_attach_args.
              segs   The array of bus_dma_segment_t's filled in by
                     bus_dmamem_alloc(), representing the memory regions to
                     map.
              nsegs  The number of segments in segs.
              size   The size of the mapping.
              kvap   Filled in to specify the kernel virtual address where the
                     memory is mapped.
              flags  Flags are defined as follows:
                     BUS_DMA_WAITOK    It is safe to wait (sleep) for
                                       resources during this call.
                     BUS_DMA_NOWAIT    It is not safe to wait (sleep) for
                                       resources during this call.
                     BUS_DMA_BUS[1-4]  These flags are placeholders, and may
                                       be used by busses to provide bus-depen-
                                       dent functionality.
                     BUS_DMA_COHERENT  This flag is a hint to machine-depen-
                                       dent code.  If possible, map the memory
                                       in such a way as it will be DMA coher-
                                       ent.  This may include mapping the
                                       pages into uncached address space or
                                       setting the cache-inhibit bits in page
                                       table entries.  If DMA coherent map-
                                       pings are impossible, this flag is
                                       silently ignored.

                                       Later, when this memory is loaded into
                                       a DMA map, machine-dependent code will
                                       take whatever steps are necessary to
                                       determine if the memory was mapped in a
                                       DMA coherent fashion.  This may include
                                       checking if the kernel virtual address
                                       lies within uncached address space or
                                       if the cache-inhibit bits are set in
                                       page table entries.  If it is deter-
                                       mined that the mapping is DMA coherent,
                                       state may be placed into the DMA map
                                       for use by later calls to
                                       bus_dmamap_sync().

                                       Note that a device driver must not rely
                                       on BUS_DMA_COHERENT for correct opera-
                                       tion.  All calls to bus_dmamap_sync()
                                       must still be made.  This flag is pro-
                                       vided only as an optimization hint to
                                       machine-dependent code.

                                       Also note that this flag only applies
                                       to coherency between the CPU and mem-
                                       ory.  Coherency between memory and the
                                       device is controlled with a different
                                       flag.  See the description of the
                                       bus_dmamap_load() function.
                     BUS_DMA_NOCACHE   This flag is a hint to machine-depen-
                                       dent code.  If possible, map the
                                       uncached memory.  This flag may be use-
                                       ful in the case that the memory cache
                                       causes unexpected behavior of the
                                       device.

              Behavior is undefined if invalid arguments are passed to
              bus_dmamem_map().

              Returns 0 on success, or an error code indicating mode of fail-
              ure.

     bus_dmamem_unmap(tag, kva, size)
              Unmaps memory previously mapped with bus_dmamem_map(), freeing
              the kernel virtual address space used by the mapping.  The argu-
              ments are as follows:
              tag   This is the bus_dma_tag_t passed down from the parent
                    driver via <bus>_attach_args.
              kva   The kernel virtual address of the mapped memory.
              size  The size of the mapping.

              Behavior is undefined if invalid arguments are passed to
              bus_dmamem_unmap().

              If given valid arguments, bus_dmamem_unmap() always succeeds.

     bus_dmamem_mmap(tag, segs, nsegs, off, prot, flags)
              Provides support for user mmap(2)'ing of DMA-safe memory.  This
              function is to be called by a device driver's (*d_mmap)() entry
              point, which is called by the device pager for each page to be
              mapped.  The arguments are as follows:
              tag    This is the bus_dma_tag_t passed down from the parent
                     driver via <bus>_attach_args.
              segs   The array of bus_dma_segment_t's filled in by
                     bus_dmamem_alloc(), representing the memory to be
                     mmap(2)'ed.
              nsegs  The number of elements in the segs array.
              off    The offset of the page in DMA memory which is to be
                     mapped.
              prot   The protection codes for the mapping.
              flags  Flags are defined as follows:
                     BUS_DMA_WAITOK    It is safe to wait (sleep) for
                                       resources during this call.
                     BUS_DMA_NOWAIT    It is not safe to wait (sleep) for
                                       resources during this call.
                     BUS_DMA_BUS[1-4]  These flags are placeholders, and may
                                       be used by busses to provide bus-depen-
                                       dent functionality.
                     BUS_DMA_COHERENT  See bus_dmamem_map() above for a
                                       description of this flag.
                     BUS_DMA_NOCACHE   See bus_dmamem_map() above for a
                                       description of this flag.

              Behavior is undefined if invalid arguments are passed to
              bus_dmamem_mmap().

              Returns -1 to indicate failure.  Otherwise, returns an opaque
              value to be interpreted by the device pager.

     bus_dmatag_subregion(tag, min_addr, max_addr, newtag, flags)
              Given a bus_dma_tag_t create a new bus_dma_tag_t with a limited
              bus address space.  This function should not normally be used,
              but is useful for devices that do not support the full address
              space of the parent bus.  The arguments are as follows:
              tag       This is the bus_dma_tag_t to subregion.
              min_addr  The smallest address this new tag can address.
              max_addr.
                        The largest address this new tag can address.
              newtag    Pointer filled in with the address of the new
                        bus_dma_tag_t.
              flags     Flags are defined as follows:
                        BUS_DMA_WAITOK  It is safe to wait (sleep) for
                                        resources during this call.
                        BUS_DMA_NOWAIT  It is not safe to wait (sleep) for
                                        resources during this call.

     bus_dmatag_destroy(tag)
              Free a tag created by bus_dmatag_subregion().

SEE ALSO
     bus_space(9), mb(9)

     Jason Thorpe, "A Machine-Independent DMA Framework for NetBSD",
     Proceedings of the FREENIX track: 1998 USENIX Annual Technical
     Conference, pp. 1-12, 1998.

HISTORY
     The bus_dma interface appeared in NetBSD 1.3.

AUTHORS
     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.

NetBSD 5.0.1                   February 19, 2009                  NetBSD 5.0.1

You can also request any man page by name and (optionally) by section:

Command: 
Section: 
Architecture: 
Collection: 
 

Use the DEFAULT collection to view manual pages for third-party software.


©1994 Man-cgi 1.15, Panagiotis Christias <christia@softlab.ntua.gr>
©1996-2014 Modified for NetBSD by Kimmo Suominen