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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);

     u_int8_t
     bus_space_read_1(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset);

     u_int16_t
     bus_space_read_2(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset);

     u_int32_t
     bus_space_read_4(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset);

     u_int64_t
     bus_space_read_8(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset);

     u_int8_t
     bus_space_read_stream_1(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset);

     u_int16_t
     bus_space_read_stream_2(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset);

     u_int32_t
     bus_space_read_stream_4(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset);

     u_int64_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, u_int8_t value);

     void
     bus_space_write_2(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset, u_int16_t value);

     void
     bus_space_write_4(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset, u_int32_t value);

     void
     bus_space_write_8(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset, u_int64_t value);

     void
     bus_space_write_stream_1(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset, u_int8_t value);

     void
     bus_space_write_stream_2(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset, u_int16_t value);

     void
     bus_space_write_stream_4(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset, u_int32_t value);

     void
     bus_space_write_stream_8(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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, u_int8_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, u_int16_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, u_int32_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, u_int64_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 #include
     <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 busses 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 #include <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 busses 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.  Busses 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 busses 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.

TYPES

     Several types are defined in #include <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 VME, and for spaces which coexist with those spaces (e.g.
     EISA and 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 busses 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.