BUS_SPACE(9)                 OpenBSD Kernel Manual                BUS_SPACE(9)

NAME
     bus_space, bus_space_alloc, bus_space_barrier, bus_space_copy_1,
     bus_space_copy_2, bus_space_copy_4, bus_space_copy_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_raw_multi_2, bus_space_read_raw_multi_4,
     bus_space_read_raw_multi_8, bus_space_read_region_1,
     bus_space_read_region_2, bus_space_read_region_4,
     bus_space_read_region_8, bus_space_read_raw_region_2,
     bus_space_read_raw_region_4, bus_space_read_raw_region_8,
     bus_space_set_multi_1, bus_space_set_multi_2, bus_space_set_multi_4,
     bus_space_set_multi_8, bus_space_set_region_1, bus_space_set_region_2,
     bus_space_set_region_4, bus_space_set_region_8, bus_space_subregion,
     bus_space_unmap, bus_space_vaddr, 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_raw_multi_2,
     bus_space_write_raw_multi_4, bus_space_write_raw_multi_8,
     bus_space_write_region_1, bus_space_write_region_2,
     bus_space_write_region_4, bus_space_write_region_8,
     bus_space_write_raw_region_2, bus_space_write_raw_region_4,
     bus_space_write_raw_region_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 cacheable, 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 cacheable, 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);

     void *
     bus_space_vaddr(bus_space_tag_t space, bus_space_handle_t handle);

     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);

     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_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_raw_region_2(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_raw_region_4(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_raw_region_8(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_1(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset,
             const 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,
             const 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,
             const 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,
             const u_int64_t *datap, bus_size_t count);

     void
     bus_space_write_raw_region_2(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset,
             const u_int8_t *datap, bus_size_t count);

     void
     bus_space_write_raw_region_4(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset,
             const u_int8_t *datap, bus_size_t count);

     void
     bus_space_write_raw_region_8(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset,
             const u_int8_t *datap, bus_size_t count);

     void
     bus_space_copy_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_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_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_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_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_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_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_raw_multi_2(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset, u_int8_t *datap,
             bus_size_t size);

     void
     bus_space_read_raw_multi_4(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset, u_int8_t *datap,
             bus_size_t size);

     void
     bus_space_read_raw_multi_8(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset, u_int8_t *datap,
             bus_size_t size);

     void
     bus_space_write_multi_1(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset, const u_int8_t *datap, bus_size_t size);

     void
     bus_space_write_multi_2(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset, const u_int16_t *datap, bus_size_t size);

     void
     bus_space_write_multi_4(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset, const u_int32_t *datap, bus_size_t size);

     void
     bus_space_write_multi_8(bus_space_tag_t space, bus_space_handle_t handle,
             bus_size_t offset, const u_int64_t *datap, bus_size_t size);

     void
     bus_space_write_raw_multi_2(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset,
             const u_int8_t *datap, bus_size_t size);

     void
     bus_space_write_raw_multi_4(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset,
             const u_int8_t *datap, bus_size_t size);

     void
     bus_space_write_raw_multi_8(bus_space_tag_t space,
             bus_space_handle_t handle, bus_size_t offset,
             const u_int8_t *datap, bus_size_t size);

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 memo-
     ry space on a second system.  On a third system, architectural limita-
     tions 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 ar-
     chitecture.  The goal of the bus_space functions is to allow a single
     driver source file to manipulate a set of devices on different system ar-
     chitectures, and to allow a single driver object file to manipulate a set
     of devices on multiple bus types on a single architecture.

     Not all buses have to implement all functions described in this document,
     though that is encouraged if the operations are logically supported by
     the bus.  Unimplemented functions should cause compile-time errors if
     possible.

     All of the interface definitions described in this document are shown as
     function prototypes and discussed as if they were required to be func-
     tions.  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 mul-
     tiple different bus space tags.  Individual buses or devices on a machine
     may use more than one bus space tag.  For instance, ISA devices are given
     an ISA memory space tag and an ISA I/O space tag.  Architectures may have
     several different tags which represent the same type of space, for in-
     stance because of multiple different host bus interface chipsets.

     A range in bus space is described by a bus address and a bus size.  The
     bus address describes the start of the range in bus space.  The bus size
     describes the size of the range in bytes.  Buses which are not byte ad-
     dressable 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 han-
     dles, which are usually created by mapping a specific range of a bus
     space.  Handles may also be created by allocating and mapping a range of
     bus space, the actual location of which is picked by the implementation
     within bounds specified by the caller of the allocation function.

     All of the bus space access functions require one bus space tag argument,
     at least one handle argument, and at least one offset argument (a bus
     size).  The bus space tag specifies the space, each handle specifies a
     region in the space, and each offset specifies the offset into the region
     of the actual location(s) to be accessed.  Offsets are given in bytes,
     though buses may impose alignment constraints.  The offset used to access
     data relative to a given handle must be such that all of the data being
     accessed is in the mapped region that the handle describes.  Trying to
     access data outside that region is an error.

     Because some architectures' memory systems use buffering to improve memo-
     ry 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 bar-
     rier 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 ad-
     dresses being accessed to be naturally aligned (i.e. base address of han-
     dle added to offset is a multiple of the access size), and that the sys-
     tem 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 inten-
     tionally (via panic) or unintentionally (by causing a fatal trap or by
     some other means) or may cause improper operation which is not immediate-
     ly fatal.  Functions which return void or which return data read from bus
     space (i.e. functions which don't 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 un-
     signed 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 map-
     ping regions and offsets into regions when performing space access opera-
     tions.

     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're 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
     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, cacheable, 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 unde-
     fined state.

     The cacheable argument controls how the space is to be mapped.  Supported
     flags include:

           BUS_SPACE_MAP_CACHEABLE  Try to map the space so that access can be
                                    cached by the system cache.  If this flag
                                    is not specified, the implementation
                                    should map the space so that it will not
                                    be cached.  This mapping method will only
                                    be useful in very rare occasions.

                                    This flag must have a value of 1 on all
                                    implementations for backward compatibili-
                                    ty.

           BUS_SPACE_MAP_PREFETCHABLE
                                    Try to map the space so that accesses can
                                    be prefetched by the system, and writes
                                    can be buffered.  This means, accesses
                                    should be side effect free (idempotent).
                                    The bus_space_barrier() methods will flush
                                    the write buffer or force actual read ac-
                                    cesses.  If this flag is not specified,
                                    the implementation should map the space so
                                    that it will not be prefetched or delayed.

           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).  The
                                    bus_space_vaddr() method can be used to
                                    obtain the kernel virtual address of the
                                    mapped range.  This is useful when soft-
                                    ware 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.  Use of this mapping
                                    method is not encouraged for normal device
                                    access; where linear access is not essen-
                                    tial, use of the bus_space_read/write()
                                    methods is strongly recommended.

     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_PREFETCHABLE 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 fol-
     lowed for maximum compatibility.  On some systems, requesting a mapping
     that cannot be satisfied (e.g. requesting a non-prefetchable mapping when
     the system can only provide a prefetchable 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 coexisting 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, ei-
     ther.

     This function will never fail.  If it would fail (e.g. because of an ar-
     gument 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-ze-
     ro 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 be-
     ing done on the space, and will result in undefined behaviour.  When
     bus_space_unmap() or bus_space_free() is called on a handle, all subre-
     gions of that handle become invalid.

     bus_space_vaddr(tag, handle)

     This method returns the kernel virtual address of a mapped bus space if
     and only if it was mapped with the BUS_SPACE_MAP_LINEAR flag.  The range
     can be accessed by normal (volatile) pointer dereferences.  If mapped
     with the BUS_SPACE_MAP_PREFETCHABLE flag, the bus_space_barrier() method
     must be used to force a particular access order.

ALLOCATING AND FREEING BUS SPACE
     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 capabili-
     ties.

     bus_space_alloc(space, reg_start, reg_end, size, alignment, boundary,
     cacheable, 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 con-
     straint 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 con-
     straint, 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 cacheable 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 unde-
     fined behaviour.  The bus_space_subregion() function can be used on han-
     dles 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, ei-
     ther.

     This function will never fail.  If it would fail (e.g. because of an ar-
     gument 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 func-
     tions provide the ability to read and write 1, 2, 4, and 8 byte data
     items on buses which support those access sizes.

     bus_space_read_1(space, handle, offset)
     bus_space_read_2(space, handle, offset)
     bus_space_read_4(space, handle, offset)
     bus_space_read_8(space, handle, offset)

     The bus_space_read_N() family of functions reads a 1, 2, 4, or 8 byte da-
     ta 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 un-
     less 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 pan-
     ic.  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 writ-
     ten.  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 execut-
     ed 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 pan-
     ic.  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 off-
     set 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 sec-
     ond 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.  Of-
     ten, drivers want to copy the contents of those buffers to or from memo-
     ry, 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 val-
     ue.  The bus_space_copy_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 (de-
     pending 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 re-
     spect 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 pan-
     ic.  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 re-
     spect 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 pan-
     ic.  In that case, they will never return.

     bus_space_copy_1(space, srchandle, srcoffset, dsthandle, dstoffset,
     count)
     bus_space_copy_2(space, srchandle, srcoffset, dsthandle, dstoffset,
     count)
     bus_space_copy_4(space, srchandle, srcoffset, dsthandle, dstoffset,
     count)
     bus_space_copy_8(space, srchandle, srcoffset, dsthandle, dstoffset,
     count)

     The bus_space_copy_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 respec-
     tive handles.

     For portability, the starting addresses of the regions specified by each
     handle plus its respective offset should be a multiple of the size of da-
     ta 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_N() functions may be
     executed in any order.  They may also be executed out of order with re-
     spect 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 exe-
     cuted by the bus_space_copy_N() functions.

     Overlapping copies between different subregions of a single region of bus
     space are handled correctly by the bus_space_copy_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 pan-
     ic.  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 off-
     set 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 incor-
     rect 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 re-
     spect 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 pan-
     ic.  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 de-
     vices' 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_write_multi_N(), and
     bus_space_set_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 ex-
     ecuted out of order with respect to other pending read and write opera-
     tions unless order is enforced by use of the bus_space_barrier() func-
     tion.  Because the bus_space_read_multi_N() functions read the same bus
     space location multiple times, they place an implicit read barrier be-
     tween 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 pan-
     ic.  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 opera-
     tions unless order is enforced by use of the bus_space_barrier() func-
     tion.  Because the bus_space_write_multi_N() functions write the same bus
     space location multiple times, they place an implicit write barrier be-
     tween 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 pan-
     ic.  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() family of functions writes the 1, 2, 4, or 8
     byte value value into bus space count times at byte offset offset in the
     region specified by handle of the bus space specified by space.  The lo-
     cation being written must lie within the bus space region specified by
     handle.

     For portability, the address specified by handle plus the offset should
     be a multiple of the size of the data value being written.  On some sys-
     tems, not obeying these requirements may cause incorrect data to be writ-
     ten, on others it may cause a system crash.

     Write operations done by the bus_space_set_multi_N() functions may be ex-
     ecuted out of order with respect to other pending read and write opera-
     tions unless order is enforced by use of the bus_space_barrier() func-
     tion.  Because the bus_space_set_multi_N() functions write the same bus
     space location multiple times, they place an implicit write barrier be-
     tween 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 pan-
     ic.  In that case, they will never return.

RAW 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_*_raw_*_N()
     functions.

     bus_space_read_raw_multi_2(space, handle, offset, datap, size)
     bus_space_read_raw_multi_4(space, handle, offset, datap, size)
     bus_space_read_raw_multi_8(space, handle, offset, datap, size)
     bus_space_read_raw_region_2(space, handle, offset, datap, size)
     bus_space_read_raw_region_4(space, handle, offset, datap, size)
     bus_space_read_raw_region_8(space, handle, offset, datap, size)
     bus_space_write_raw_multi_2(space, handle, offset, datap, size)
     bus_space_write_raw_multi_4(space, handle, offset, datap, size)
     bus_space_write_raw_multi_8(space, handle, offset, datap, size)
     bus_space_write_raw_region_2(space, handle, offset, datap, size)
     bus_space_write_raw_region_4(space, handle, offset, datap, size)
     bus_space_write_raw_region_8(space, handle, offset, datap, size)

     These functions, unlike their non-raw counterparts, all take a u_int8_t
     pointer for the datap argument and a byte count for the size argument re-
     gardless of the access width being requested.

     datap must reference a buffer that is correctly aligned for the access
     width being requested or the results are undefined.

     size must be a multiple of the access width or the results are undefined.

     In all other respects these functions are the same as their non-raw coun-
     terparts.  Please consult the documentation for those functions for fur-
     ther information.

EXPECTED CHANGES TO THE BUS_SPACE FUNCTIONS
     The definition of the bus_space functions should not yet be considered
     finalized.  There are several changes and improvements which should be
     explored, including:

     o   Providing a mechanism by which incorrectly-written drivers will be
         automatically given barriers and properly-written drivers won't be
         forced to use more barriers than they need.  This should probably be
         done via a #define in the incorrectly-written drivers.  Unfortunate-
         ly, at this time, few drivers actually use barriers correctly (or at
         all).  Because of that, bus_space implementations on architectures
         which do buffering must always do the barriers inside the bus_space
         calls, to be safe.  That has a potentially significant performance
         impact.

     o   Exporting the bus_space functions to user-land so that applications
         (such as X servers) have easier, more portable access to device
         space.

     o   Redefining bus space tags and handles so that machine-independent bus
         interface drivers (for example PCI to VME bridges) could define and
         implement bus spaces without requiring machine-dependent code.  If
         this is done, it should be done in such a way that machine-dependent
         optimizations should remain possible.

     o   Converting bus spaces (such as PCI configuration space) which cur-
         rently use space-specific access methods to use the bus_space func-
         tions where that is appropriate.

     o   Redefining the way bus space is mapped and allocated, so that mapping
         and allocation are done with bus specific functions which return bus
         space tags.  This would allow further optimization than is currently
         possible, and would also ease translation of the bus_space functions
         into user space (since mapping in user space would look like it just
         used a different bus-specific mapping function).

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 OpenBSD development team added the *_raw_* API, and discarded the
     *_stream_* API.

AUTHORS
     The bus_space interfaces were designed and implemented by the NetBSD de-
     veloper 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 develop-
     ment.

     Chris Demetriou wrote this manual page.

     Niklas Hallqvist did the *_raw_* API for OpenBSD.

OpenBSD 4.1                    November 20, 2000                            16
