Provided by: freebsd-manpages_12.2-1_all 
NAME
bus_space, bus_space_barrier, bus_space_copy_region_1, bus_space_copy_region_2, bus_space_copy_region_4,
bus_space_copy_region_8, bus_space_copy_region_stream_1, bus_space_copy_region_stream_2,
bus_space_copy_region_stream_4, bus_space_copy_region_stream_8, bus_space_free, bus_space_map,
bus_space_read_1, bus_space_read_2, bus_space_read_4, bus_space_read_8, bus_space_read_multi_1,
bus_space_read_multi_2, bus_space_read_multi_4, bus_space_read_multi_8, bus_space_read_multi_stream_1,
bus_space_read_multi_stream_2, bus_space_read_multi_stream_4, bus_space_read_multi_stream_8,
bus_space_read_region_1, bus_space_read_region_2, bus_space_read_region_4, bus_space_read_region_8,
bus_space_read_region_stream_1, bus_space_read_region_stream_2, bus_space_read_region_stream_4,
bus_space_read_region_stream_8, bus_space_read_stream_1, bus_space_read_stream_2, bus_space_read_stream_4,
bus_space_read_stream_8, bus_space_set_multi_1, bus_space_set_multi_2, bus_space_set_multi_4,
bus_space_set_multi_8, bus_space_set_multi_stream_1, bus_space_set_multi_stream_2,
bus_space_set_multi_stream_4, bus_space_set_multi_stream_8, bus_space_set_region_1, bus_space_set_region_2,
bus_space_set_region_4, bus_space_set_region_8, bus_space_set_region_stream_1,
bus_space_set_region_stream_2, bus_space_set_region_stream_4, bus_space_set_region_stream_8,
bus_space_subregion, bus_space_unmap, bus_space_write_1, bus_space_write_2, bus_space_write_4,
bus_space_write_8, bus_space_write_multi_1, bus_space_write_multi_2, bus_space_write_multi_4,
bus_space_write_multi_8, bus_space_write_multi_stream_1, bus_space_write_multi_stream_2,
bus_space_write_multi_stream_4, bus_space_write_multi_stream_8, bus_space_write_region_1,
bus_space_write_region_2, bus_space_write_region_4, bus_space_write_region_8,
bus_space_write_region_stream_1, bus_space_write_region_stream_2, bus_space_write_region_stream_4,
bus_space_write_region_stream_8, bus_space_write_stream_1, bus_space_write_stream_2,
bus_space_write_stream_4, bus_space_write_stream_8 — bus space manipulation functions
SYNOPSIS
#include <machine/bus.h>
int
bus_space_map(bus_space_tag_t space, bus_addr_t address, bus_size_t size, int flags,
bus_space_handle_t *handlep);
void
bus_space_unmap(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t size);
int
bus_space_subregion(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, bus_size_t size,
bus_space_handle_t *nhandlep);
int
bus_space_alloc(bus_space_tag_t space, bus_addr_t reg_start, bus_addr_t reg_end, bus_size_t size,
bus_size_t alignment, bus_size_t boundary, int flags, bus_addr_t *addrp, bus_space_handle_t *handlep);
void
bus_space_free(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t size);
uint8_t
bus_space_read_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset);
uint16_t
bus_space_read_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset);
uint32_t
bus_space_read_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset);
uint64_t
bus_space_read_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset);
uint8_t
bus_space_read_stream_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset);
uint16_t
bus_space_read_stream_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset);
uint32_t
bus_space_read_stream_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset);
uint64_t
bus_space_read_stream_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset);
void
bus_space_write_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint8_t value);
void
bus_space_write_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint16_t value);
void
bus_space_write_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint32_t value);
void
bus_space_write_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint64_t value);
void
bus_space_write_stream_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t value);
void
bus_space_write_stream_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t value);
void
bus_space_write_stream_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t value);
void
bus_space_write_stream_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t value);
void
bus_space_barrier(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, bus_size_t length,
int flags);
void
bus_space_read_region_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t *datap, bus_size_t count);
void
bus_space_read_region_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t *datap, bus_size_t count);
void
bus_space_read_region_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t *datap, bus_size_t count);
void
bus_space_read_region_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t *datap, bus_size_t count);
void
bus_space_read_region_stream_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t *datap, bus_size_t count);
void
bus_space_read_region_stream_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t *datap, bus_size_t count);
void
bus_space_read_region_stream_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t *datap, bus_size_t count);
void
bus_space_read_region_stream_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t *datap, bus_size_t count);
void
bus_space_write_region_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t *datap, bus_size_t count);
void
bus_space_write_region_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t *datap, bus_size_t count);
void
bus_space_write_region_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t *datap, bus_size_t count);
void
bus_space_write_region_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t *datap, bus_size_t count);
void
bus_space_write_region_stream_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t *datap, bus_size_t count);
void
bus_space_write_region_stream_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t *datap, bus_size_t count);
void
bus_space_write_region_stream_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t *datap, bus_size_t count);
void
bus_space_write_region_stream_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t *datap, bus_size_t count);
void
bus_space_copy_region_1(bus_space_tag_t space, bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset, bus_size_t count);
void
bus_space_copy_region_2(bus_space_tag_t space, bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset, bus_size_t count);
void
bus_space_copy_region_4(bus_space_tag_t space, bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset, bus_size_t count);
void
bus_space_copy_region_8(bus_space_tag_t space, bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset, bus_size_t count);
void
bus_space_copy_region_stream_1(bus_space_tag_t space, bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset, bus_size_t count);
void
bus_space_copy_region_stream_2(bus_space_tag_t space, bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset, bus_size_t count);
void
bus_space_copy_region_stream_4(bus_space_tag_t space, bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset, bus_size_t count);
void
bus_space_copy_region_stream_8(bus_space_tag_t space, bus_space_handle_t srchandle, bus_size_t srcoffset,
bus_space_handle_t dsthandle, bus_size_t dstoffset, bus_size_t count);
void
bus_space_set_region_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint8_t value,
bus_size_t count);
void
bus_space_set_region_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint16_t value,
bus_size_t count);
void
bus_space_set_region_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint32_t value,
bus_size_t count);
void
bus_space_set_region_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint64_t value,
bus_size_t count);
void
bus_space_set_region_stream_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t value, bus_size_t count);
void
bus_space_set_region_stream_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t value, bus_size_t count);
void
bus_space_set_region_stream_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t value, bus_size_t count);
void
bus_space_set_region_stream_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t value, bus_size_t count);
void
bus_space_read_multi_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint8_t *datap,
bus_size_t count);
void
bus_space_read_multi_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t *datap, bus_size_t count);
void
bus_space_read_multi_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t *datap, bus_size_t count);
void
bus_space_read_multi_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t *datap, bus_size_t count);
void
bus_space_read_multi_stream_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t *datap, bus_size_t count);
void
bus_space_read_multi_stream_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t *datap, bus_size_t count);
void
bus_space_read_multi_stream_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t *datap, bus_size_t count);
void
bus_space_read_multi_stream_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t *datap, bus_size_t count);
void
bus_space_write_multi_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t *datap, bus_size_t count);
void
bus_space_write_multi_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t *datap, bus_size_t count);
void
bus_space_write_multi_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t *datap, bus_size_t count);
void
bus_space_write_multi_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t *datap, bus_size_t count);
void
bus_space_write_multi_stream_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t *datap, bus_size_t count);
void
bus_space_write_multi_stream_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t *datap, bus_size_t count);
void
bus_space_write_multi_stream_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t *datap, bus_size_t count);
void
bus_space_write_multi_stream_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t *datap, bus_size_t count);
void
bus_space_set_multi_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint8_t value,
bus_size_t count);
void
bus_space_set_multi_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint16_t value,
bus_size_t count);
void
bus_space_set_multi_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint32_t value,
bus_size_t count);
void
bus_space_set_multi_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset, uint64_t value,
bus_size_t count);
void
bus_space_set_multi_stream_1(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint8_t value, bus_size_t count);
void
bus_space_set_multi_stream_2(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint16_t value, bus_size_t count);
void
bus_space_set_multi_stream_4(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint32_t value, bus_size_t count);
void
bus_space_set_multi_stream_8(bus_space_tag_t space, bus_space_handle_t handle, bus_size_t offset,
uint64_t value, bus_size_t count);
DESCRIPTION
The bus_space functions exist to allow device drivers machine-independent access to bus memory and register
areas. All of the functions and types described in this document can be used by including the
<machine/bus.h> header file.
Many common devices are used on multiple architectures, but are accessed differently on each because of
architectural constraints. For instance, a device which is mapped in one system's I/O space may be mapped
in memory space on a second system. On a third system, architectural limitations might change the way
registers need to be accessed (e.g. creating a non-linear register space). In some cases, a single driver
may need to access the same type of device in multiple ways in a single system or architecture. The goal
of the bus_space functions is to allow a single driver source file to manipulate a set of devices on
different system architectures, and to allow a single driver object file to manipulate a set of devices on
multiple bus types on a single architecture.
Not all buses have to implement all functions described in this document, though that is encouraged if the
operations are logically supported by the bus. Unimplemented functions should cause compile-time errors if
possible.
All of the interface definitions described in this document are shown as function prototypes and discussed
as if they were required to be functions. Implementations are encouraged to implement prototyped (type-
checked) versions of these interfaces, but may implement them as macros if appropriate. Machine-dependent
types, variables, and functions should be marked clearly in <machine/bus.h> to avoid confusion with the
machine-independent types and functions, and, if possible, should be given names which make the machine-
dependence clear.
CONCEPTS AND GUIDELINES
Bus spaces are described by bus space tags, which can be created only by machine-dependent code. A given
machine may have several different types of bus space (e.g. memory space and I/O space), and thus may
provide multiple different bus space tags. Individual buses or devices on a machine may use more than one
bus space tag. For instance, ISA devices are given an ISA memory space tag and an ISA I/O space tag.
Architectures may have several different tags which represent the same type of space, for instance because
of multiple different host bus interface chipsets.
A range in bus space is described by a bus address and a bus size. The bus address describes the start of
the range in bus space. The bus size describes the size of the range in bytes. Buses which are not byte
addressable may require use of bus space ranges with appropriately aligned addresses and properly rounded
sizes.
Access to regions of bus space is facilitated by use of bus space handles, which are usually created by
mapping a specific range of a bus space. Handles may also be created by allocating and mapping a range of
bus space, the actual location of which is picked by the implementation within bounds specified by the
caller of the allocation function.
All of the bus space access functions require one bus space tag argument, at least one handle argument, and
at least one offset argument (a bus size). The bus space tag specifies the space, each handle specifies a
region in the space, and each offset specifies the offset into the region of the actual location(s) to be
accessed. Offsets are given in bytes, though buses may impose alignment constraints. The offset used to
access data relative to a given handle must be such that all of the data being accessed is in the mapped
region that the handle describes. Trying to access data outside that region is an error.
Because some architectures' memory systems use buffering to improve memory and device access performance,
there is a mechanism which can be used to create “barriers” in the bus space read and write stream. There
are three types of barriers: read, write, and read/write. All reads started to the region before a read
barrier must complete before any reads after the read barrier are started. (The analogous requirement is
true for write barriers.) Read/write barriers force all reads and writes started before the barrier to
complete before any reads or writes after the barrier are started. Correctly-written drivers will include
all appropriate barriers, and assume only the read/write ordering imposed by the barrier operations.
People trying to write portable drivers with the bus_space functions should try to make minimal assumptions
about what the system allows. In particular, they should expect that the system requires bus space
addresses being accessed to be naturally aligned (i.e., base address of handle added to offset is a
multiple of the access size), and that the system does alignment checking on pointers (i.e., pointer to
objects being read and written must point to properly-aligned data).
The descriptions of the bus_space functions given below all assume that they are called with proper
arguments. If called with invalid arguments or arguments that are out of range (e.g. trying to access data
outside of the region mapped when a given handle was created), undefined behaviour results. In that case,
they may cause the system to halt, either intentionally (via panic) or unintentionally (by causing a fatal
trap of by some other means) or may cause improper operation which is not immediately fatal. Functions
which return void or which return data read from bus space (i.e., functions which do not obviously return
an error code) do not fail. They could only fail if given invalid arguments, and in that case their
behaviour is undefined. Functions which take a count of bytes have undefined results if the specified
count is zero.
TYPES
Several types are defined in <machine/bus.h> to facilitate use of the bus_space functions by drivers.
bus_addr_t
The bus_addr_t type is used to describe bus addresses. It must be an unsigned integral type capable of
holding the largest bus address usable by the architecture. This type is primarily used when mapping and
unmapping bus space.
bus_size_t
The bus_size_t type is used to describe sizes of ranges in bus space. It must be an unsigned integral type
capable of holding the size of the largest bus address range usable on the architecture. This type is used
by virtually all of the bus_space functions, describing sizes when mapping regions and offsets into regions
when performing space access operations.
bus_space_tag_t
The bus_space_tag_t type is used to describe a particular bus space on a machine. Its contents are
machine-dependent and should be considered opaque by machine-independent code. This type is used by all
bus_space functions to name the space on which they are operating.
bus_space_handle_t
The bus_space_handle_t type is used to describe a mapping of a range of bus space. Its contents are
machine-dependent and should be considered opaque by machine-independent code. This type is used when
performing bus space access operations.
MAPPING AND UNMAPPING BUS SPACE
This section is specific to the NetBSD version of these functions and may or may not apply to the FreeBSD
version.
Bus space must be mapped before it can be used, and should be unmapped when it is no longer needed. The
bus_space_map() and bus_space_unmap() functions provide these capabilities.
Some drivers need to be able to pass a subregion of already-mapped bus space to another driver or module
within a driver. The bus_space_subregion() function allows such subregions to be created.
bus_space_map(space, address, size, flags, handlep)
The bus_space_map() function maps the region of bus space named by the space, address, and size arguments.
If successful, it returns zero and fills in the bus space handle pointed to by handlep with the handle that
can be used to access the mapped region. If unsuccessful, it will return non-zero and leave the bus space
handle pointed to by handlep in an undefined state.
The flags argument controls how the space is to be mapped. Supported flags include:
BUS_SPACE_MAP_CACHEABLE Try to map the space so that accesses can be cached and/or prefetched by the
system. If this flag is not specified, the implementation should map the space so
that it will not be cached or prefetched.
This flag must have a value of 1 on all implementations for backward
compatibility.
BUS_SPACE_MAP_LINEAR Try to map the space so that its contents can be accessed linearly via normal
memory access methods (e.g. pointer dereferencing and structure accesses). This
is useful when software wants to do direct access to a memory device, e.g. a frame
buffer. If this flag is specified and linear mapping is not possible, the
bus_space_map() call should fail. If this flag is not specified, the system may
map the space in whatever way is most convenient.
Not all combinations of flags make sense or are supported with all spaces. For instance,
BUS_SPACE_MAP_CACHEABLE may be meaningless when used on many systems' I/O port spaces, and on some systems
BUS_SPACE_MAP_LINEAR without BUS_SPACE_MAP_CACHEABLE may never work. When the system hardware or firmware
provides hints as to how spaces should be mapped (e.g. the PCI memory mapping registers' “prefetchable”
bit), those hints should be followed for maximum compatibility. On some systems, requesting a mapping that
cannot be satisfied (e.g. requesting a non-cacheable mapping when the system can only provide a cacheable
one) will cause the request to fail.
Some implementations may keep track of use of bus space for some or all bus spaces and refuse to allow
duplicate allocations. This is encouraged for bus spaces which have no notion of slot-specific space
addressing, such as ISA, and for spaces which coexist with those spaces (e.g. PCI memory and I/O spaces co-
existing with ISA memory and I/O spaces).
Mapped regions may contain areas for which there is no device on the bus. If space in those areas is
accessed, the results are bus-dependent.
bus_space_unmap(space, handle, size)
The bus_space_unmap() function unmaps a region of bus space mapped with bus_space_map(). When unmapping a
region, the size specified should be the same as the size given to bus_space_map() when mapping that
region.
After bus_space_unmap() is called on a handle, that handle is no longer valid. (If copies were made of the
handle they are no longer valid, either.)
This function will never fail. If it would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, bus_space_unmap() will never return.
bus_space_subregion(space, handle, offset, size, nhandlep)
The bus_space_subregion() function is a convenience function which makes a new handle to some subregion of
an already-mapped region of bus space. The subregion described by the new handle starts at byte offset
offset into the region described by handle, with the size give by size, and must be wholly contained within
the original region.
If successful, bus_space_subregion() returns zero and fills in the bus space handle pointed to by nhandlep.
If unsuccessful, it returns non-zero and leaves the bus space handle pointed to by nhandlep in an undefined
state. In either case, the handle described by handle remains valid and is unmodified.
When done with a handle created by bus_space_subregion(), the handle should be thrown away. Under no
circumstances should bus_space_unmap() be used on the handle. Doing so may confuse any resource management
being done on the space, and will result in undefined behaviour. When bus_space_unmap() or
bus_space_free() is called on a handle, all subregions of that handle become invalid.
ALLOCATING AND FREEING BUS SPACE
This section is specific to the NetBSD version of these functions and may or may not apply to the FreeBSD
version.
Some devices require or allow bus space to be allocated by the operating system for device use. When the
devices no longer need the space, the operating system should free it for use by other devices. The
bus_space_alloc() and bus_space_free() functions provide these capabilities.
bus_space_alloc(space, reg_start, reg_end, size, alignment, boundary, flags, addrp, handlep)
The bus_space_alloc() function allocates and maps a region of bus space with the size given by size,
corresponding to the given constraints. If successful, it returns zero, fills in the bus address pointed
to by addrp with the bus space address of the allocated region, and fills in the bus space handle pointed
to by handlep with the handle that can be used to access that region. If unsuccessful, it returns non-zero
and leaves the bus address pointed to by addrp and the bus space handle pointed to by handlep in an
undefined state.
Constraints on the allocation are given by the reg_start, reg_end, alignment, and boundary parameters. The
allocated region will start at or after reg_start and end before or at reg_end. The alignment constraint
must be a power of two, and the allocated region will start at an address that is an even multiple of that
power of two. The boundary constraint, if non-zero, ensures that the region is allocated so that first
address in region / boundary has the same value as last address in region / boundary. If the constraints
cannot be met, bus_space_alloc() will fail. It is an error to specify a set of constraints that can never
be met (for example, size greater than boundary).
The flags parameter is the same as the like-named parameter to bus_space_map(), the same flag values should
be used, and they have the same meanings.
Handles created by bus_space_alloc() should only be freed with bus_space_free(). Trying to use
bus_space_unmap() on them causes undefined behaviour. The bus_space_subregion() function can be used on
handles created by bus_space_alloc().
bus_space_free(space, handle, size)
The bus_space_free() function unmaps and frees a region of bus space mapped and allocated with
bus_space_alloc(). When unmapping a region, the size specified should be the same as the size given to
bus_space_alloc() when allocating the region.
After bus_space_free() is called on a handle, that handle is no longer valid. (If copies were made of the
handle, they are no longer valid, either.)
This function will never fail. If it would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, bus_space_free() will never return.
READING AND WRITING SINGLE DATA ITEMS
The simplest way to access bus space is to read or write a single data item. The bus_space_read_N() and
bus_space_write_N() families of functions provide the ability to read and write 1, 2, 4, and 8 byte data
items on buses which support those access sizes.
bus_space_read_1(space, handle, offset)
bus_space_read_2(space, handle, offset)
bus_space_read_4(space, handle, offset)
bus_space_read_8(space, handle, offset)
The bus_space_read_N() family of functions reads a 1, 2, 4, or 8 byte data item from the offset specified
by offset into the region specified by handle of the bus space specified by space. The location being read
must lie within the bus space region specified by handle.
For portability, the starting address of the region specified by handle plus the offset should be a
multiple of the size of data item being read. On some systems, not obeying this requirement may cause
incorrect data to be read, on others it may cause a system crash.
Read operations done by the bus_space_read_N() functions may be executed out of order with respect to other
pending read and write operations unless order is enforced by use of the bus_space_barrier() function.
These functions will never fail. If they would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, they will never return.
bus_space_write_1(space, handle, offset, value)
bus_space_write_2(space, handle, offset, value)
bus_space_write_4(space, handle, offset, value)
bus_space_write_8(space, handle, offset, value)
The bus_space_write_N() family of functions writes a 1, 2, 4, or 8 byte data item to the offset specified
by offset into the region specified by handle of the bus space specified by space. The location being
written must lie within the bus space region specified by handle.
For portability, the starting address of the region specified by handle plus the offset should be a
multiple of the size of data item being written. On some systems, not obeying this requirement may cause
incorrect data to be written, on others it may cause a system crash.
Write operations done by the bus_space_write_N() functions may be executed out of order with respect to
other pending read and write operations unless order is enforced by use of the bus_space_barrier()
function.
These functions will never fail. If they would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, they will never return.
BARRIERS
In order to allow high-performance buffering implementations to avoid bus activity on every operation, read
and write ordering should be specified explicitly by drivers when necessary. The bus_space_barrier()
function provides that ability.
bus_space_barrier(space, handle, offset, length, flags)
The bus_space_barrier() function enforces ordering of bus space read and write operations for the specified
subregion (described by the offset and length parameters) of the region named by handle in the space named
by space.
The flags argument controls what types of operations are to be ordered. Supported flags are:
BUS_SPACE_BARRIER_READ Synchronize read operations.
BUS_SPACE_BARRIER_WRITE Synchronize write operations.
Those flags can be combined (or-ed together) to enforce ordering on both read and write operations.
All of the specified type(s) of operation which are done to the region before the barrier operation are
guaranteed to complete before any of the specified type(s) of operation done after the barrier.
Example: Consider a hypothetical device with two single-byte ports, one write-only input port (at offset 0)
and a read-only output port (at offset 1). Operation of the device is as follows: data bytes are written
to the input port, and are placed by the device on a stack, the top of which is read by reading from the
output port. The sequence to correctly write two data bytes to the device then read those two data bytes
back would be:
/*
* t and h are the tag and handle for the mapped device's
* space.
*/
bus_space_write_1(t, h, 0, data0);
bus_space_barrier(t, h, 0, 1, BUS_SPACE_BARRIER_WRITE); /* 1 */
bus_space_write_1(t, h, 0, data1);
bus_space_barrier(t, h, 0, 2,
BUS_SPACE_BARRIER_READ|BUS_SPACE_BARRIER_WRITE); /* 2 */
ndata1 = bus_space_read_1(t, h, 1);
bus_space_barrier(t, h, 1, 1, BUS_SPACE_BARRIER_READ); /* 3 */
ndata0 = bus_space_read_1(t, h, 1);
/* data0 == ndata0, data1 == ndata1 */
The first barrier makes sure that the first write finishes before the second write is issued, so that two
writes to the input port are done in order and are not collapsed into a single write. This ensures that
the data bytes are written to the device correctly and in order.
The second barrier makes sure that the writes to the output port finish before any of the reads to the
input port are issued, thereby making sure that all of the writes are finished before data is read. This
ensures that the first byte read from the device really is the last one that was written.
The third barrier makes sure that the first read finishes before the second read is issued, ensuring that
data is read correctly and in order.
The barriers in the example above are specified to cover the absolute minimum number of bus space
locations. It is correct (and often easier) to make barrier operations cover the device's whole range of
bus space, that is, to specify an offset of zero and the size of the whole region.
REGION OPERATIONS
Some devices use buffers which are mapped as regions in bus space. Often, drivers want to copy the
contents of those buffers to or from memory, e.g. into mbufs which can be passed to higher levels of the
system or from mbufs to be output to a network. In order to allow drivers to do this as efficiently as
possible, the bus_space_read_region_N() and bus_space_write_region_N() families of functions are provided.
Drivers occasionally need to copy one region of a bus space to another, or to set all locations in a region
of bus space to contain a single value. The bus_space_copy_region_N() family of functions and the
bus_space_set_region_N() family of functions allow drivers to perform these operations.
bus_space_read_region_1(space, handle, offset, datap, count)
bus_space_read_region_2(space, handle, offset, datap, count)
bus_space_read_region_4(space, handle, offset, datap, count)
bus_space_read_region_8(space, handle, offset, datap, count)
The bus_space_read_region_N() family of functions reads count 1, 2, 4, or 8 byte data items from bus space
starting at byte offset offset in the region specified by handle of the bus space specified by space and
writes them into the array specified by datap. Each successive data item is read from an offset 1, 2, 4,
or 8 bytes after the previous data item (depending on which function is used). All locations being read
must lie within the bus space region specified by handle.
For portability, the starting address of the region specified by handle plus the offset should be a
multiple of the size of data items being read and the data array pointer should be properly aligned. On
some systems, not obeying these requirements may cause incorrect data to be read, on others it may cause a
system crash.
Read operations done by the bus_space_read_region_N() functions may be executed in any order. They may
also be executed out of order with respect to other pending read and write operations unless order is
enforced by use of the bus_space_barrier() function. There is no way to insert barriers between reads of
individual bus space locations executed by the bus_space_read_region_N() functions.
These functions will never fail. If they would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, they will never return.
bus_space_write_region_1(space, handle, offset, datap, count)
bus_space_write_region_2(space, handle, offset, datap, count)
bus_space_write_region_4(space, handle, offset, datap, count)
bus_space_write_region_8(space, handle, offset, datap, count)
The bus_space_write_region_N() family of functions reads count 1, 2, 4, or 8 byte data items from the array
specified by datap and writes them to bus space starting at byte offset offset in the region specified by
handle of the bus space specified by space. Each successive data item is written to an offset 1, 2, 4, or
8 bytes after the previous data item (depending on which function is used). All locations being written
must lie within the bus space region specified by handle.
For portability, the starting address of the region specified by handle plus the offset should be a
multiple of the size of data items being written and the data array pointer should be properly aligned. On
some systems, not obeying these requirements may cause incorrect data to be written, on others it may cause
a system crash.
Write operations done by the bus_space_write_region_N() functions may be executed in any order. They may
also be executed out of order with respect to other pending read and write operations unless order is
enforced by use of the bus_space_barrier() function. There is no way to insert barriers between writes of
individual bus space locations executed by the bus_space_write_region_N() functions.
These functions will never fail. If they would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, they will never return.
bus_space_copy_region_1(space, srchandle, srcoffset, dsthandle, dstoffset, count)
bus_space_copy_region_2(space, srchandle, srcoffset, dsthandle, dstoffset, count)
bus_space_copy_region_4(space, srchandle, srcoffset, dsthandle, dstoffset, count)
bus_space_copy_region_8(space, srchandle, srcoffset, dsthandle, dstoffset, count)
The bus_space_copy_region_N() family of functions copies count 1, 2, 4, or 8 byte data items in bus space
from the area starting at byte offset srcoffset in the region specified by srchandle of the bus space
specified by space to the area starting at byte offset dstoffset in the region specified by dsthandle in
the same bus space. Each successive data item read or written has an offset 1, 2, 4, or 8 bytes after the
previous data item (depending on which function is used). All locations being read and written must lie
within the bus space region specified by their respective handles.
For portability, the starting addresses of the regions specified by the each handle plus its respective
offset should be a multiple of the size of data items being copied. On some systems, not obeying this
requirement may cause incorrect data to be copied, on others it may cause a system crash.
Read and write operations done by the bus_space_copy_region_N() functions may be executed in any order.
They may also be executed out of order with respect to other pending read and write operations unless order
is enforced by use of the bus_space_barrier() function. There is no way to insert barriers between reads
or writes of individual bus space locations executed by the bus_space_copy_region_N() functions.
Overlapping copies between different subregions of a single region of bus space are handled correctly by
the bus_space_copy_region_N() functions.
These functions will never fail. If they would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, they will never return.
bus_space_set_region_1(space, handle, offset, value, count)
bus_space_set_region_2(space, handle, offset, value, count)
bus_space_set_region_4(space, handle, offset, value, count)
bus_space_set_region_8(space, handle, offset, value, count)
The bus_space_set_region_N() family of functions writes the given value to count 1, 2, 4, or 8 byte data
items in bus space starting at byte offset offset in the region specified by handle of the bus space
specified by space. Each successive data item has an offset 1, 2, 4, or 8 bytes after the previous data
item (depending on which function is used). All locations being written must lie within the bus space
region specified by handle.
For portability, the starting address of the region specified by handle plus the offset should be a
multiple of the size of data items being written. On some systems, not obeying this requirement may cause
incorrect data to be written, on others it may cause a system crash.
Write operations done by the bus_space_set_region_N() functions may be executed in any order. They may
also be executed out of order with respect to other pending read and write operations unless order is
enforced by use of the bus_space_barrier() function. There is no way to insert barriers between writes of
individual bus space locations executed by the bus_space_set_region_N() functions.
These functions will never fail. If they would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, they will never return.
READING AND WRITING A SINGLE LOCATION MULTIPLE TIMES
Some devices implement single locations in bus space which are to be read or written multiple times to
communicate data, e.g. some ethernet devices' packet buffer FIFOs. In order to allow drivers to manipulate
these types of devices as efficiently as possible, the bus_space_read_multi_N(), bus_space_set_multi_N(),
and bus_space_write_multi_N() families of functions are provided.
bus_space_read_multi_1(space, handle, offset, datap, count)
bus_space_read_multi_2(space, handle, offset, datap, count)
bus_space_read_multi_4(space, handle, offset, datap, count)
bus_space_read_multi_8(space, handle, offset, datap, count)
The bus_space_read_multi_N() family of functions reads count 1, 2, 4, or 8 byte data items from bus space
at byte offset offset in the region specified by handle of the bus space specified by space and writes them
into the array specified by datap. Each successive data item is read from the same location in bus space.
The location being read must lie within the bus space region specified by handle.
For portability, the starting address of the region specified by handle plus the offset should be a
multiple of the size of data items being read and the data array pointer should be properly aligned. On
some systems, not obeying these requirements may cause incorrect data to be read, on others it may cause a
system crash.
Read operations done by the bus_space_read_multi_N() functions may be executed out of order with respect to
other pending read and write operations unless order is enforced by use of the bus_space_barrier()
function. Because the bus_space_read_multi_N() functions read the same bus space location multiple times,
they place an implicit read barrier between each successive read of that bus space location.
These functions will never fail. If they would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, they will never return.
bus_space_write_multi_1(space, handle, offset, datap, count)
bus_space_write_multi_2(space, handle, offset, datap, count)
bus_space_write_multi_4(space, handle, offset, datap, count)
bus_space_write_multi_8(space, handle, offset, datap, count)
The bus_space_write_multi_N() family of functions reads count 1, 2, 4, or 8 byte data items from the array
specified by datap and writes them into bus space at byte offset offset in the region specified by handle
of the bus space specified by space. Each successive data item is written to the same location in bus
space. The location being written must lie within the bus space region specified by handle.
For portability, the starting address of the region specified by handle plus the offset should be a
multiple of the size of data items being written and the data array pointer should be properly aligned. On
some systems, not obeying these requirements may cause incorrect data to be written, on others it may cause
a system crash.
Write operations done by the bus_space_write_multi_N() functions may be executed out of order with respect
to other pending read and write operations unless order is enforced by use of the bus_space_barrier()
function. Because the bus_space_write_multi_N() functions write the same bus space location multiple
times, they place an implicit write barrier between each successive write of that bus space location.
These functions will never fail. If they would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, they will never return.
bus_space_set_multi_1(space, handle, offset, value, count)
bus_space_set_multi_2(space, handle, offset, value, count)
bus_space_set_multi_4(space, handle, offset, value, count)
bus_space_set_multi_8(space, handle, offset, value, count)
The bus_space_set_multi_N() writes value into bus space at byte offset offset in the region specified by
handle of the bus space specified by space, count times. The location being written must lie within the
bus space region specified by handle.
For portability, the starting address of the region specified by handle plus the offset should be a
multiple of the size of data items being written and the data array pointer should be properly aligned. On
some systems, not obeying these requirements may cause incorrect data to be written, on others it may cause
a system crash.
Write operations done by the bus_space_set_multi_N() functions may be executed out of order with respect to
other pending read and write operations unless order is enforced by use of the bus_space_barrier()
function. Because the bus_space_set_multi_N() functions write the same bus space location multiple times,
they place an implicit write barrier between each successive write of that bus space location.
These functions will never fail. If they would fail (e.g. because of an argument error), that indicates a
software bug which should cause a panic. In that case, they will never return.
STREAM FUNCTIONS
Most of the bus_space functions imply a host byte-order and a bus byte-order and take care of any
translation for the caller. In some cases, however, hardware may map a FIFO or some other memory region
for which the caller may want to use multi-word, yet untranslated access. Access to these types of memory
regions should be with the bus_space_*_stream_N() functions.
bus_space_read_stream_1()
bus_space_read_stream_2()
bus_space_read_stream_4()
bus_space_read_stream_8()
bus_space_read_multi_stream_1()
bus_space_read_multi_stream_2()
bus_space_read_multi_stream_4()
bus_space_read_multi_stream_8()
bus_space_read_region_stream_1()
bus_space_read_region_stream_2()
bus_space_read_region_stream_4()
bus_space_read_region_stream_8()
bus_space_write_stream_1()
bus_space_write_stream_2()
bus_space_write_stream_4()
bus_space_write_stream_8()
bus_space_write_multi_stream_1()
bus_space_write_multi_stream_2()
bus_space_write_multi_stream_4()
bus_space_write_multi_stream_8()
bus_space_write_region_stream_1()
bus_space_write_region_stream_2()
bus_space_write_region_stream_4()
bus_space_write_region_stream_8()
bus_space_copy_region_stream_1()
bus_space_copy_region_stream_2()
bus_space_copy_region_stream_4()
bus_space_copy_region_stream_8()
bus_space_set_multi_stream_1()
bus_space_set_multi_stream_2()
bus_space_set_multi_stream_4()
bus_space_set_multi_stream_8()
bus_space_set_region_stream_1()
bus_space_set_region_stream_2()
bus_space_set_region_stream_4()
bus_space_set_region_stream_8()
These functions are defined just as their non-stream counterparts, except that they provide no byte-order
translation.
COMPATIBILITY
The current NetBSD version of the bus_space interface specification differs slightly from the original
specification that came into wide use and FreeBSD adopted. A few of the function names and arguments have
changed for consistency and increased functionality.
SEE ALSO
bus_dma(9)
HISTORY
The bus_space functions were introduced in a different form (memory and I/O spaces were accessed via
different sets of functions) in NetBSD 1.2. The functions were merged to work on generic “spaces” early in
the NetBSD 1.3 development cycle, and many drivers were converted to use them. This document was written
later during the NetBSD 1.3 development cycle, and the specification was updated to fix some consistency
problems and to add some missing functionality.
The manual page was then adapted to the version of the interface that FreeBSD imported for the CAM SCSI
drivers, plus subsequent evolution. The FreeBSD bus_space version was imported in FreeBSD 3.0.
AUTHORS
The bus_space interfaces were designed and implemented by the NetBSD developer community. Primary
contributors and implementors were Chris Demetriou, Jason Thorpe, and Charles Hannum, but the rest of the
NetBSD developers and the user community played a significant role in development.
Justin Gibbs ported these interfaces to FreeBSD.
Chris Demetriou wrote this manual page.
Warner Losh modified it for the FreeBSD implementation.
BUGS
This manual may not completely and accurately document the interface, and many parts of the interface are
unspecified.