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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);

     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 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 <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.  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 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.