bus_dmamap_create (9)
Leading comments
Copyright (c) 2002, 2003 Hiten M. Pandya. All rights reserved. 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, without modification, immediately at the beginning of the file. 2. The name of the author may not be used to endorse or promote products derived from th...
NAME
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 InterfaceSYNOPSIS
In machine/bus.h Ft int Fn 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 Ft int Fn bus_dma_tag_destroy bus_dma_tag_t dmat Ft int Fn bus_dmamap_create bus_dma_tag_t dmat int flags bus_dmamap_t *mapp Ft int Fn bus_dmamap_destroy bus_dma_tag_t dmat bus_dmamap_t map Ft int Fn 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 Ft int Fn 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 Ft int Fn 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 Ft int Fn 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 Ft int Fn 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 Ft int Fn 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 Ft void Fn bus_dmamap_unload bus_dma_tag_t dmat bus_dmamap_t map Ft void Fn bus_dmamap_sync bus_dma_tag_t dmat bus_dmamap_t map op Ft int Fn bus_dmamem_alloc bus_dma_tag_t dmat void **vaddr int flags bus_dmamap_t *mapp Ft void Fn bus_dmamem_free bus_dma_tag_t dmat void *vaddr bus_dmamap_t mapDESCRIPTION
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 ifconfig 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 limitations.
STRUCTURES AND TYPES
- Vt bus_dma_tag_t
- 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.
- Vt bus_dma_filter_t
-
Client specified address filter having the format:
- Ft int
- Fn 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 Fa filtarg argument is specified by the client during tag creation to be passed to all invocations of the callback. The Fa testaddr argument contains a potential starting address of a DMA mapping. The filter function operates on the set of addresses from Fa 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.
- Vt bus_dma_segment_t
-
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 Fa ds_addr field contains the device visible address of the DMA segment, and Fa 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 device.
- Vt bus_dmamap_t
- 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.
- Vt bus_dmamap_callback_t
-
Client specified callback for receiving mapping information resulting from
the load of a
Vt bus_dmamap_t
via
Fn bus_dmamap_load ,
Fn bus_dmamap_load_bio
or
Fn bus_dmamap_load_ccb .
Callbacks are of the format:
- Ft void
- Fn client_callback void *callback_arg bus_dma_segment_t *segs int nseg int error
The Fa callback_arg is the callback argument passed to dmamap load functions. The Fa segs and Fa nseg arguments describe an array of Vt 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 Fa error argument. More information on the use of callbacks can be found in the description of the individual dmamap load functions.
- Vt bus_dmamap_callback2_t
-
Client specified callback for receiving mapping information resulting from
the load of a
Vt bus_dmamap_t
via
Fn bus_dmamap_load_uio
or
Fn bus_dmamap_load_mbuf .
Callback2s are of the format:
- Ft void
- Fn 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 Vt bus_dmamap_callback_t with the addition that the length of the data mapped is provided via Fa mapsize .
- Vt bus_dmasync_op_t
-
Memory synchronization operation specifier.
Bus DMA requires explicit synchronization of memory with its device
visible mapping in order to guarantee memory coherency.
The
Vt 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
Fn 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_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.
- Vt bus_dma_lock_t
-
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:
- Ft void
- Fn lockfunc void *lockfunc_arg bus_dma_lock_op_t op
The Fa lockfuncarg argument is specified by the client during tag creation to be passed to all invocations of the callback. The Fa op argument specifies the lock operation to perform.
Two Vt lockfunc implementations are provided for convenience. Fn busdma_lock_mutex performs standard mutex operations on the sleep mutex provided via Fa lockfuncarg . Fn dflt_lock will generate a system panic if it is called. It is substituted into the tag when Fa lockfunc is passed as NULL to Fn bus_dma_tag_create and is useful for tags that should not be used with deferred load operations.
- Vt bus_dma_lock_op_t
-
Operations to be performed by the client-specified
Fn lockfunc .
- BUS_DMA_LOCK
- Acquires and/or locks the client locking primitive.
- BUS_DMA_UNLOCK
- Releases and/or unlocks the client locking primitive.
FUNCTIONS
- Fn 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 provided:
- Fa parent
- Indicates restrictions between the parent bridge, CPU memory, and the device. Each device must use a master parent tag by calling Fn bus_get_dma_tag .
- Fa 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
- Fa 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 Vt 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.
- Fa 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 Fa lowaddr and less than or equal to Fa highaddr . For example, a device incapable of DMA above 4GB, would specify a Fa highaddr of BUS_SPACE_MAXADDR and a Fa lowaddr of BUS_SPACE_MAXADDR_32BIT Similarly a device that can only perform DMA to addresses below 16MB would specify a Fa highaddr of BUS_SPACE_MAXADDR and a Fa 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 window.
- Fa filtfunc
- Optional filter function (may be NULL to be called for any attempt to map memory into the window described by Fa lowaddr and Fa highaddr . A filter function is only required when the single window described by Fa lowaddr and Fa highaddr cannot adequately describe the constraints of the device. The filter function will be called for every machine page that overlaps the exclusion window.
- Fa filtfuncarg
- Argument passed to all calls to the filter function for this tag. May be NULL
- Fa maxsize
- Maximum size, in bytes, of the sum of all segment lengths in a given DMA mapping associated with this tag.
- Fa nsegments
- Number of discontinuities (scatter/gather segments) allowed in a DMA mapped region. If there is no restriction, BUS_SPACE_UNRESTRICTED may be specified.
- Fa maxsegsz
- Maximum size, in bytes, of a segment in any DMA mapped region associated with Fa dmat .
- Fa 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, Er ENOMEM is returned. This should not be used for tags that only describe buffers that will be allocated with Fn 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 optimization.
- Fa 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, Fn dflt_lock is used.
- Fa lockfuncarg
- Optional argument to be passed to the function specified by Fa lockfunc .
- Fa dmat
- Pointer to a bus_dma_tag_t where the resulting DMA tag will be stored.
Returns Er ENOMEM if sufficient memory is not available for tag creation or allocating mapping resources.
- Fn bus_dma_tag_destroy dmat
-
Deallocate the DMA tag
Fa dmat
that was created by
Fn bus_dma_tag_create .
Returns Er EBUSY if any DMA maps remain associated with Fa dmat or `0' on success.
- Fn bus_dmamap_create dmat flags *mapp
-
Allocates and initializes a DMA map.
Arguments are as follows:
- Fa dmat
- DMA tag.
- Fa 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 Fn bus_dmamap_sync , but it may reduce the cost of performing these operations. For Fn bus_dmamap_create , the BUS_DMA_COHERENT flag is currently implemented on sparc64.
- Fa mapp
- Pointer to a Vt bus_dmamap_t where the resulting DMA map will be stored.
Returns Er ENOMEM if sufficient memory is not available for creating the map or allocating mapping resources.
- Fn bus_dmamap_destroy dmat map
-
Frees all resources associated with a given DMA map.
Arguments are as follows:
- Fa dmat
- DMA tag used to allocate Fa map .
- Fa map
- The DMA map to destroy.
Returns Er EBUSY if a mapping is still active for Fa map .
- Fn bus_dmamap_load dmat map buf buflen *callback
-
"callback_arg" "flags"
Creates a mapping in device visible address space of
Fa buflen
bytes of
Fa buf ,
associated with the DMA map
Fa map .
This call will always return immediately and will not block for any reason.
Arguments are as follows:
- Fa dmat
- DMA tag used to allocate Fa map .
- Fa map
- A DMA map without a currently active mapping.
- Fa buf
- A kernel virtual address pointer to a contiguous (in KVA) buffer, to be mapped into device visible address space.
- Fa buflen
- The size of the buffer.
- Fa callback Fa 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.
- Fa 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.
- BUS_DMA_NOCACHE
- The generated transactions to and from the virtual page are non-cacheable. For Fn 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.
- Er EINPROGRESS
-
The mapping has been deferred for lack of resources.
The callback will be called as soon as resources are available.
Callbacks are serviced in FIFO order.
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.
- Er ENOMEM
- The load request has failed due to insufficient resources, and the caller specifically used the BUS_DMA_NOWAIT flag.
- Er EINVAL
- The load request was invalid. The callback has been called and has been provided the same error. This error value may indicate that Fa dmat , Fa map , Fa buf , or Fa callback were invalid, or Fa buflen was larger than the Fa maxsize argument used to create the dma tag Fa 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 Fa dm_segs callback argument contains an array of Vt bus_dma_segment_t elements describing the mapping. This array is only valid during the scope of the callback function.
- Er EFBIG
- A mapping could not be achieved within the segment constraints provided in the tag even though the requested allocation size was less than maxsize.
- Fn bus_dmamap_load_bio dmat map bio callback callback_arg flags
- This is a variation of Fn bus_dmamap_load which maps buffers pointed to by Fa bio for DMA transfers. Fa bio may point to either a mapped or unmapped buffer.
- Fn bus_dmamap_load_ccb dmat map ccb callback callback_arg flags
-
This is a variation of
Fn bus_dmamap_load
which maps data pointed to by
Fa ccb
for DMA transfers.
The data for
Fa 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 Vt struct bio attached to the CCB.
Fn bus_dmamap_load_ccb supports the following CCB XPT function codes:
- XPT_ATA_IO
- XPT_CONT_TARGET_IO
- XPT_SCSI_IO
- Fn bus_dmamap_load_mbuf dmat map mbuf callback2 callback_arg
-
"flags"
This is a variation of
Fn bus_dmamap_load
which maps mbuf chains
for DMA transfers.
A
Vt bus_size_t
argument is also passed to the callback routine, which
contains the mbuf chain's packet header length.
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 Fn bus_dmamap_load , Er EINVAL will be returned if the size of the mbuf chain exceeds the maximum limit of the DMA tag.
- Fn bus_dmamap_load_mbuf_sg dmat map mbuf segs nsegs flags
- This is just like Fn 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 Fn bus_dmamap_load_mbuf .
- Fn bus_dmamap_load_uio dmat map uio callback2 callback_arg flags
-
This is a variation of
Fn bus_dmamap_load
which maps buffers pointed to by
Fa uio
for DMA transfers.
A
Vt bus_size_t
argument is also passed to the callback routine, which contains the size of
Fa uio ,
i.e.
Fa uio->uio_resid .
The
BUS_DMA_NOWAIT
flag is implied, thus no callback deferral will happen.
Returns the same errors as
Fn bus_dmamap_load .
If Fa uio->uio_segflg is UIO_USERSPACE then it is assumed that the buffer, Fa uio is in Fa uio->uio_td->td_proc Ns 's address space. User space memory must be in-core and wired prior to attempting a map load operation. Pages may be locked using vslock(9).
- Fn bus_dmamap_unload dmat map
-
Unloads a DMA map.
Arguments are as follows:
- Fa dmat
- DMA tag used to allocate Fa map .
- Fa map
- The DMA map that is to be unloaded.
Fn bus_dmamap_unload will not perform any implicit synchronization of DMA buffers. This must be done explicitly by a call to Fn bus_dmamap_sync prior to unloading the map.
- Fn bus_dmamap_sync dmat map op
-
Performs synchronization of a device visible mapping with the CPU visible
memory referenced by that mapping.
Arguments are as follows:
- Fa dmat
- DMA tag used to allocate Fa map .
- Fa map
- The DMA mapping to be synchronized.
- Fa op
- Type of synchronization operation to perform. See the definition of Vt bus_dmasync_op_t for a description of the acceptable values for Fa op .
The Fn 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 performed.
If read and write operations are not preceded and followed by the appropriate synchronization operations, behavior is undefined.
- Fn bus_dmamem_alloc dmat **vaddr flags *mapp
-
Allocates memory that is mapped into KVA at the address returned
in
Fa vaddr
and that is permanently loaded into the newly created
Vt bus_dmamap_t
returned via
Fa mapp .
Arguments are as follows:
- Fa dmat
- DMA tag describing the constraints of the DMA mapping.
- Fa vaddr
- Pointer to a pointer that will hold the returned KVA mapping of the allocated region.
- Fa 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.
- BUS_DMA_COHERENT
- Attempt to map this memory in a coherent fashion. See Fn bus_dmamap_create above for a description of this flag. For Fn 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.
- BUS_DMA_NOCACHE
- The allocated memory will not be cached in the processor caches. All memory accesses appear on the bus and are executed without reordering. For Fn 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.
- Fa mapp
- Pointer to a Vt bus_dmamap_t where the resulting DMA map will be stored.
The size of memory to be allocated is Fa maxsize as specified in the call to Fn bus_dma_tag_create for Fa dmat .
The current implementation of Fn 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 Fn 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 Fn bus_dmamap_sync section still apply and should be used to achieve portability on architectures without coherent buses.
Returns Er ENOMEM if sufficient memory is not available for completing the operation.
- Fn bus_dmamem_free dmat *vaddr map
-
Frees memory previously allocated by
Fn bus_dmamem_alloc .
Any mappings
will be invalidated.
Arguments are as follows:
- Fa dmat
- DMA tag.
- Fa vaddr
- Kernel virtual address of the memory.
- Fa map
- DMA map to be invalidated.
RETURN VALUES
Behavior is undefined if invalid arguments are passed to any of the above functions. If sufficient resources cannot be allocated for a given transaction, Er ENOMEM is returned. All routines that are not of type Vt void will return 0 on success or an error code on failure as discussed above.All Vt void routines will succeed if provided with valid arguments.
LOCKING
Two locking protocols are used by . 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 ifconfig and is not exposed to clients of the API.The second protocol involves protecting various resources stored in the tag. Since almost all ifconfig 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 ifconfig 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 Fn bus_dmamap_load callback function is called from a deferred context instead of the driver context. This means that certain ifconfig functions must always be called with the same lock held that is specified in the tag. These functions include:
- Fn bus_dmamap_load
- Fn bus_dmamap_load_bio
- Fn bus_dmamap_load_ccb
- Fn bus_dmamap_load_mbuf
- Fn bus_dmamap_load_mbuf_sg
- Fn bus_dmamap_load_uio
- Fn bus_dmamap_unload
- Fn bus_dmamap_sync
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 ifconfig 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:
- Fn bus_dma_tag_create
- Fn bus_dmamap_create
- Fn bus_dmamem_alloc
All other functions do not have a locking protocol and can thus be called with or without any system or driver locks held.
SEE ALSO
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"
HISTORY
The ifconfig interface first appeared in Nx 1.3 .The ifconfig API was adopted from Nx for use in the CAM SCSI subsystem. The alterations to the original API were aimed to remove the need for a Vt bus_dma_segment_t array stored in each Vt bus_dmamap_t while allowing callers to queue up on scarce resources.
AUTHORS
The ifconfig interface was designed and implemented by An Jason R. Thorpe of the Numerical Aerospace Simulation Facility, NASA Ames Research Center. Additional input on the ifconfig design was provided by An -nosplit An Chris Demetriou , An Charles Hannum , An Ross Harvey , An Matthew Jacob , An Jonathan Stone , and An Matt Thomas .The ifconfig interface in Fx benefits from the contributions of An Justin T. Gibbs , An Peter Wemm , An Doug Rabson , An Matthew N. Dodd , An Sam Leffler , An Maxime Henrion , An Jake Burkholder , An Takahashi Yoshihiro , An Scott Long and many others.
This manual page was written by An Hiten M. Pandya and An Justin T. Gibbs .