.\" $NetBSD: bus_dma.9,v 1.67.2.2 2024/10/04 11:40:54 martin Exp $ .\" .\" Copyright (c) 1996, 1997, 1998, 2001, 2005, 2006 The NetBSD Foundation, Inc. .\" All rights reserved. .\" .\" This code is derived from software contributed to The NetBSD Foundation .\" by Jason R. Thorpe of the Numerical Aerospace Simulation Facility, .\" NASA Ames Research Center. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS .\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS .\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS .\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN .\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .Dd February 17, 2024 .Dt BUS_DMA 9 .Os .Sh NAME .Nm bus_dma , .Nm bus_dmamap_create , .Nm bus_dmamap_destroy , .Nm bus_dmamap_load , .Nm bus_dmamap_load_mbuf , .Nm bus_dmamap_load_uio , .Nm bus_dmamap_load_raw , .Nm bus_dmamap_unload , .Nm bus_dmamap_sync , .Nm bus_dmamem_alloc , .Nm bus_dmamem_free , .Nm bus_dmamem_map , .Nm bus_dmamem_unmap , .Nm bus_dmamem_mmap , .Nm bus_dmatag_subregion , .Nm bus_dmatag_destroy .Nd Bus and Machine Independent DMA Mapping Interface .Sh SYNOPSIS .In sys/bus.h .Ft int .Fn 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" .Ft void .Fn bus_dmamap_destroy "bus_dma_tag_t tag" "bus_dmamap_t dmam" .Ft int .Fn bus_dmamap_load "bus_dma_tag_t tag" "bus_dmamap_t dmam" "void *buf" \ "bus_size_t buflen" "struct proc *p" "int flags" .Ft int .Fn bus_dmamap_load_mbuf "bus_dma_tag_t tag" "bus_dmamap_t dmam" \ "struct mbuf *chain" "int flags" .Ft int .Fn bus_dmamap_load_uio "bus_dma_tag_t tag" "bus_dmamap_t dmam" \ "struct uio *uio" "int flags" .Ft int .Fn 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" .Ft void .Fn bus_dmamap_unload "bus_dma_tag_t tag" "bus_dmamap_t dmam" .Ft void .Fn bus_dmamap_sync "bus_dma_tag_t tag" "bus_dmamap_t dmam" \ "bus_addr_t offset" "bus_size_t len" "int ops" .Ft int .Fn 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" .Ft void .Fn bus_dmamem_free "bus_dma_tag_t tag" "bus_dma_segment_t *segs" "int nsegs" .Ft int .Fn bus_dmamem_map "bus_dma_tag_t tag" "bus_dma_segment_t *segs" "int nsegs" \ "size_t size" "void **kvap" "int flags" .Ft void .Fn bus_dmamem_unmap "bus_dma_tag_t tag" "void *kva" "size_t size" .Ft paddr_t .Fn bus_dmamem_mmap "bus_dma_tag_t tag" "bus_dma_segment_t *segs" \ "int nsegs" "off_t off" "int prot" "int flags" .Ft int .Fn 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" .Ft void .Fn bus_dmatag_destroy "bus_dma_tag_t tag" .Sh DESCRIPTION Provide a bus- and machine-independent "DMA mapping interface." .Sh IMPLEMENTATION NOTES All data types and constants will be defined by the port-specific header .In machine/bus_defs.h . All functions will be defined by the port-specific header .In machine/bus_funcs.h . Note that this document assumes the existence of types already defined by the current "bus.h" interface. .Pp Unless otherwise noted, all function calls in this interface may be defined as .Xr cpp 1 macros. .Sh DATA TYPES Individual implementations may name these structures whatever they wish, providing that the external representations are: .Bl -tag -width compact .It Fa bus_dma_tag_t A machine-dependent opaque type describing the implementation of DMA for a given bus. .It Fa bus_dma_segment_t A structure with at least the following members: .Bd -literal bus_addr_t ds_addr; bus_size_t ds_len; .Ed .Pp The structure may have machine-dependent members and arbitrary layout. The values in .Fa ds_addr and .Fa ds_len are suitable for programming into DMA controller address and length registers. .It Fa bus_dmamap_t A pointer to a structure with at least the following members: .Bd -literal bus_size_t dm_maxsegsz; bus_size_t dm_mapsize; int dm_nsegs; bus_dma_segment_t *dm_segs; .Ed .Pp The structure may have machine-dependent members and arbitrary layout. The .Fa dm_maxsegsz member indicates the maximum number of bytes that may be transferred by any given DMA segment. The .Fa dm_mapsize member indicates the size of the mapping. A value of 0 indicates the mapping is invalid. The .Fa dm_segs member may be an array of segments or a pointer to an array of segments. The .Fa dm_nsegs member indicates the number of segments in .Fa dm_segs . .El .Sh FUNCTIONS .Bl -tag -width compact .It Fn 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: .Bl -tag -width nsegments -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa size This is the maximum DMA transfer that can be mapped by the handle. .It Fa 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. .It Fa maxsegsz The maximum number of bytes that may be transferred by any given DMA segment and will be assigned to the .Fa dm_maxsegsz member. .It Fa 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 .Fa boundary bytes. Mappings may begin on a boundary line but may not end on or cross a boundary line. If no boundary condition needs to be observed, a .Fa boundary argument of 0 should be used. .It Fa flags Flags are defined as follows: .Bl -tag -width BUS_DMA_ALLOCNOW -compact .It Dv BUS_DMA_WAITOK It is safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_NOWAIT It is not safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_ALLOCNOW Perform any resource allocation this handle may need now. If this is not specified, the allocation may be deferred to .Fn bus_dmamap_load . If this flag is specified, .Fn bus_dmamap_load will not block on resource allocation. .It Dv BUS_DMA_BUS[1-4] These flags are placeholders, and may be used by busses to provide bus-dependent functionality. .El .It Fa dmamp This is a pointer to a bus_dmamap_t. A DMA map will be allocated and pointed to by .Fa dmamp upon successful completion of this routine. .Fa dmamp is undefined if this routine fails. .El .Pp Behavior is not defined if invalid arguments are passed to .Fn bus_dmamap_create . .Pp Returns 0 on success, or an error code to indicate mode of failure. .It Fn bus_dmamap_destroy "tag" "dmam" Frees all resources associated with a given DMA handle. Arguments are as follows: .Bl -tag -width dmam -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa dmam The DMA handle to destroy. .El .Pp In the event that the DMA handle contains a valid mapping, the mapping will be unloaded via the same mechanism used by .Fn bus_dmamap_unload . .Pp Behavior is not defined if invalid arguments are passed to .Fn bus_dmamap_destroy . .Pp If given valid arguments, .Fn bus_dmamap_destroy always succeeds. .It Fn bus_dmamap_load "tag" "dmam" "buf" "buflen" "p" "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: .Bl -tag -width buflen -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa dmam The DMA handle with which to map the transfer. .It Fa buf The buffer to be used for the DMA transfer. .It Fa buflen The size of the buffer. .It Fa p Used to indicate the address space in which the buffer is located. If .Dv NULL , the buffer is assumed to be in kernel space. Otherwise, the buffer is assumed to be in proc .Fa p Ap s address space. .It Fa flags are defined as follows: .Bl -tag -width "BUS_DMA_STREAMING" -compact .It Dv BUS_DMA_WAITOK It is safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_NOWAIT It is not safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_STREAMING By default, the .Nm API assumes that there is coherency between memory and the device performing the DMA transaction. Some platforms, however, have special hardware, such as an .Dq 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 performing 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 feature, 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 .Fn bus_dmamem_alloc function. .It Dv BUS_DMA_READ This is a hint to the machine-dependent back-end that indicates the mapping will be used only for a .Em "device -> memory" transaction. The back-end may perform optimizations based on this information. .It Dv BUS_DMA_WRITE This is a hint to the machine-dependent back-end that indicates the mapping will be used only for a .Em "memory -> device" transaction. The back-end may perform optimizations based on this information. .It Dv BUS_DMA_BUS[1-4] These flags are placeholders, and may be used by busses to provide bus-dependent functionality. .El .El .Pp As noted above, if a DMA handle is created with .Dv BUS_DMA_ALLOCNOW , .Fn bus_dmamap_load will never block. .Pp If a call to .Fn 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 incomplete iteration through the uio. .Pp Behavior is not defined if invalid arguments are passed to .Fn bus_dmamap_load . .Pp Returns 0 on success, or an error code to indicate mode of failure. Possible error codes include the following: .Pp .Bl -tag -width dmam -compact .It Er EFBIG Too many segments. .It Er EINVAL .Fa buflen is too large for the DMA map. .It Er ENOMEM Could not allocate memory for, e.g., a bounce buffer. .El .It Fn bus_dmamap_load_mbuf "tag" "dmam" "chain" "flags" This is a variation of .Fn bus_dmamap_load which maps mbuf chains for DMA transfers. Mbuf chains are assumed to be in kernel virtual address space. .It Fn bus_dmamap_load_uio "tag" "dmam" "uio" "flags" This is a variation of .Fn bus_dmamap_load which maps buffers pointed to by .Fa uio for DMA transfers. Determination if the buffers are in user or kernel virtual address space is done internally, according to .Fa "uio->uio_vmspace" . See .Xr uiomove 9 for details of the .Dv uio structure. .It Fn bus_dmamap_load_raw "tag" "dmam" "segs" "nsegs" "size" "flags" This is a variation of .Fn bus_dmamap_load which maps buffers allocated by .Fn bus_dmamem_alloc (see below). The .Fa segs argument is an array of bus_dma_segment_t's filled in by .Fn bus_dmamem_alloc . The .Fa nsegs argument is the number of segments in the array. The .Fa size argument is the size of the DMA transfer. .It Fn bus_dmamap_unload "tag" "dmam" Deletes the mappings for a given DMA handle. Arguments are as follows: .Bl -tag -width dmam -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa dmam The DMA handle containing the mappings which are to be deleted. .El .Pp If the DMA handle was created with .Dv BUS_DMA_ALLOCNOW , .Fn bus_dmamap_unload will not free the corresponding resources which were allocated by .Fn bus_dmamap_create . This is to ensure that .Fn bus_dmamap_load will never block on resources if the handle was created with .Dv BUS_DMA_ALLOCNOW . .Pp .Fn bus_dmamap_unload will not perform any implicit synchronization of DMA buffers. This must be done explicitly by .Fn bus_dmamap_sync . .Pp .Fn bus_dmamap_unload will restore the .Fa dm_maxsegsz member to its initial value assigned by .Fn bus_dmamap_create . .Pp Behavior is not defined if invalid arguments are passed to .Fn bus_dmamap_unload . .Pp If given valid arguments, .Fn bus_dmamap_unload always succeeds. .It Fn bus_dmamap_sync "tag" "dmam" "offset" "len" "ops" Performs pre- and post-DMA operation cache and/or buffer synchronization. Arguments are as follows: .Bl -tag -width offset -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa dmam The DMA mapping to be synchronized. .It Fa offset The offset into the DMA mapping to synchronize. .It Fa len The length of the mapping from .Fa offset to synchronize. .It Fa ops One or more synchronization operation to perform. The following DMA synchronization operations are defined: .Bl -tag -width BUS_DMASYNC_POSTWRITE -compact .It Dv BUS_DMASYNC_PREREAD Perform any synchronization required prior to an update of host memory by the device. .It Dv BUS_DMASYNC_POSTREAD Perform any synchronization required after an update of host memory by the device and prior to CPU access to host memory. .It Dv BUS_DMASYNC_PREWRITE Perform any synchronization required after an update of host memory by the CPU and prior to device access to host memory. .It Dv BUS_DMASYNC_POSTWRITE Perform any synchronization required after device access to host memory. .El where each operation may involve cache flush/invalidation, bounce buffer copying, and/or memory barriers. .Pp More than one operation may performed in a given synchronization call. Mixing of .Em PRE and .Em POST operations is not allowed, and behavior is undefined if this is attempted. .El .Pp Synchronization operations are expressed from the perspective of the host RAM, e.g., a .Em "device -> memory" operation is a .Em READ and a .Em "memory -> device" operation is a .Em WRITE . .Pp .Fn 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, .Fn bus_dmamap_sync may elect to skip certain expensive operations, such as flushing of the data cache. See .Fn bus_dmamem_map for more information on this subject. .Pp On platforms which implement a weak memory access ordering model, .Fn bus_dmamap_sync will always cause the appropriate memory barriers to be issued. .Pp 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. .Pp An example of using .Fn bus_dmamap_sync , involving multiple read-write use of a single mapping might look like this: .Bd -literal 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(...); .Ed .Pp This function .Em must be called to synchronize DMA buffers before and after a DMA operation. Other .Nm functions can .Em not be relied on to do this synchronization implicitly. If DMA read and write operations are not preceded and followed by the appropriate synchronization operations, behavior is undefined. .Pp Behavior is not defined if invalid arguments are passed to .Fn bus_dmamap_sync . .Pp If given valid arguments, .Fn bus_dmamap_sync always succeeds. .It Fn bus_dmamem_alloc "tag" "size" "alignment" "boundary" "segs" "nsegs" "rsegs" "flags" Allocates memory that is "DMA safe" for the bus corresponding to the given tag. .Pp 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 .Fa segs can thus not be used to program DMA controller address registers. Only the values in the .Fa dm_segs array of a successfully loaded DMA map (using .Fn bus_dmamap_load ) can be used for this purpose. .Pp Allocations will always be rounded to the hardware page size. Callers may wish to take advantage of this, and cluster allocation of small data structures. Arguments are as follows: .Bl -tag -width alignment -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa size The amount of memory to allocate. .It Fa alignment Each segment in the allocated memory will be aligned to this value. If the alignment is less than a hardware page size, it will be rounded up to the hardware page size. This value must be a power of two. .It Fa 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. If no boundary condition needs to be observed, a .Fa boundary argument of 0 should be used. .It Fa segs An array of bus_dma_segment_t's, filled in as memory is allocated, representing the opaque addresses of the memory chunks. .It Fa nsegs Specifies the number of segments in .Fa segs , and this is the maximum number of segments that the allocated memory may contain. .It Fa rsegs Used to return the actual number of segments the memory contains. .It Fa flags Flags are defined as follows: .Bl -tag -width BUS_DMA_STREAMING -compact .It Dv BUS_DMA_WAITOK It is safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_NOWAIT It is not safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_STREAMING Adjusts, if necessary, the size, alignment, and boundary constrains to conform to the platform-dependent requirements for the use of the .Dv BUS_DMA_STREAMING flag with the .Fn bus_dmamap_load function. If the platform does not support the .Dv BUS_DMA_STREAMING feature, or if the size, alignment, and boundary constraints would already satisfy the platform's requirements, this flag is silently ignored. The .Dv BUS_DMA_STREAMING flag will never relax the constraints specified in the call. .It Dv BUS_DMA_BUS[1-4] These flags are placeholders, and may be used by busses to provide bus-dependent functionality. .El .El .Pp All pages allocated by .Fn bus_dmamem_alloc will be wired down until they are freed by .Fn bus_dmamem_free . .Pp Behavior is undefined if invalid arguments are passed to .Fn bus_dmamem_alloc . .Pp Returns 0 on success, or an error code indicating mode of failure. .It Fn bus_dmamem_free "tag" "segs" "nsegs" Frees memory previously allocated by .Fn bus_dmamem_alloc . Any mappings will be invalidated. Arguments are as follows: .Bl -tag -width nsegs -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa segs The array of bus_dma_segment_t's filled in by .Fn bus_dmamem_alloc . .It Fa nsegs The number of segments in .Fa segs . .El .Pp Behavior is undefined if invalid arguments are passed to .Fn bus_dmamem_free . .Pp If given valid arguments, .Fn bus_dmamem_free always succeeds. .It Fn bus_dmamem_map "tag" "segs" "nsegs" "size" "kvap" "flags" Maps memory allocated with .Fn bus_dmamem_alloc into kernel virtual address space. Arguments are as follows: .Bl -tag -width flags -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa segs The array of bus_dma_segment_t's filled in by .Fn bus_dmamem_alloc , representing the memory regions to map. .It Fa nsegs The number of segments in .Fa segs . .It Fa size The size of the mapping. .It Fa kvap Filled in to specify the kernel virtual address where the memory is mapped. .It Fa flags Flags are defined as follows: .Bl -tag -width BUS_DMA_COHERENT -compact .It Dv BUS_DMA_WAITOK It is safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_NOWAIT It is not safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_BUS[1-4] These flags are placeholders, and may be used by busses to provide bus-dependent functionality. .It Dv BUS_DMA_COHERENT This flag is a .Em hint to machine-dependent code. If possible, map the memory in such a way as it will be DMA coherent. This may include mapping the pages into uncached address space or setting the cache-inhibit bits in page table entries. If DMA coherent mappings are impossible, this flag is silently ignored. .Pp 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 determined that the mapping is DMA coherent, state may be placed into the DMA map for use by later calls to .Fn bus_dmamap_sync . .Pp Note that a device driver must not rely on .Dv BUS_DMA_COHERENT for correct operation. All calls to .Fn bus_dmamap_sync must still be made. This flag is provided only as an optimization hint to machine-dependent code. .Pp Also note that this flag only applies to coherency between the CPU and memory. Coherency between memory and the device is controlled with a different flag. See the description of the .Fn bus_dmamap_load function. .It Dv BUS_DMA_NOCACHE This flag is a .Em hint to machine-dependent code. If possible, map the memory uncached. This flag may be useful in the case that the memory cache causes unexpected behavior of the device. .Pp Exclusive with .Dv BUS_DMA_PREFETCHABLE . .It Dv BUS_DMA_PREFETCHABLE This flag is a .Em hint to machine-dependent code. If possible, map the memory prefetchable/write-combining. .Pp Exclusive with .Dv BUS_DMA_NOCACHE . .El .El .Pp Behavior is undefined if invalid arguments are passed to .Fn bus_dmamem_map . .Pp Returns 0 on success, or an error code indicating mode of failure. .It Fn bus_dmamem_unmap "tag" "kva" "size" Unmaps memory previously mapped with .Fn bus_dmamem_map , freeing the kernel virtual address space used by the mapping. The arguments are as follows: .Bl -tag -width size -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa kva The kernel virtual address of the mapped memory. .It Fa size The size of the mapping. .El .Pp Behavior is undefined if invalid arguments are passed to .Fn bus_dmamem_unmap . .Pp If given valid arguments, .Fn bus_dmamem_unmap always succeeds. .It Fn bus_dmamem_mmap "tag" "segs" "nsegs" "off" "prot" "flags" Provides support for user .Xr mmap 2 Ap 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: .Bl -tag -width nsegs -compact .It Fa tag This is the bus_dma_tag_t passed down from the parent driver via .Fa _attach_args . .It Fa segs The array of bus_dma_segment_t's filled in by .Fn bus_dmamem_alloc , representing the memory to be .Xr mmap 2 Ap ed . .It Fa nsegs The number of elements in the .Fa segs array. .It Fa off The offset of the page in DMA memory which is to be mapped. .It Fa prot The protection codes for the mapping. .It Fa flags Flags are defined as follows: .Bl -tag -width BUS_DMA_COHERENT -compact .It Dv BUS_DMA_WAITOK It is safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_NOWAIT It is not safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_BUS[1-4] These flags are placeholders, and may be used by busses to provide bus-dependent functionality. .It Dv BUS_DMA_COHERENT See .Fn bus_dmamem_map above for a description of this flag. .It Dv BUS_DMA_NOCACHE See .Fn bus_dmamem_map above for a description of this flag. .El .El .Pp Behavior is undefined if invalid arguments are passed to .Fn bus_dmamem_mmap . .Pp Returns -1 to indicate failure. Otherwise, returns an opaque value to be interpreted by the device pager. .It Fn 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. Not all ports implement this method; on ports where it is unavailable, .Er EOPNOTSUPP is returned. The arguments are as follows: .Bl -tag -width max_addr -compact .It Fa tag This is the bus_dma_tag_t to subregion. .It Fa min_addr The smallest address this new tag can address. .It Fa max_addr The largest address this new tag can address. .It Fa newtag Pointer filled in with the address of the new bus_dma_tag_t. .It Fa flags Flags are defined as follows: .Bl -tag -width BUS_DMA_WAITOK -compact .It Dv BUS_DMA_WAITOK It is safe to wait (sleep) for resources during this call. .It Dv BUS_DMA_NOWAIT It is not safe to wait (sleep) for resources during this call. .El .El The address range .Fa min_addr to .Fa max_addr is inclusive of both addresses. .It Fn bus_dmatag_destroy "tag" Free a tag created by .Fn bus_dmatag_subregion . .El .Sh SEE ALSO .Xr membar_ops 3 , .Xr bus_space 9 .Rs .%A Jason Thorpe .%T "A Machine-Independent DMA Framework for NetBSD" .%I USENIX Association .%B Proceedings of the FREENIX Track: 1998 USENIX Annual Technical Conference .%P 1-12 .%D June 15-19, 1998 .%U http://www.usenix.org/publications/library/proceedings/usenix98/freenix/thorpe_dma.pdf .Re .Sh HISTORY The .Nm interface appeared in .Nx 1.3 . .Sh AUTHORS .An -nosplit 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 Chris Demetriou , .An Charles Hannum , .An Ross Harvey , .An Matthew Jacob , .An Jonathan Stone , and .An Matt Thomas .