BUS_SPACE(9) | Kernel Developer's Manual | BUS_SPACE(9) |
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_free
,
bus_space_handle_is_equal
,
bus_space_is_equal
,
bus_space_map
, bus_space_mmap
,
bus_space_peek_1
,
bus_space_peek_2
,
bus_space_peek_4
,
bus_space_peek_8
,
bus_space_poke_1
,
bus_space_poke_2
,
bus_space_poke_4
,
bus_space_poke_8
,
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_release
,
bus_space_reservation_addr
,
bus_space_reservation_init
,
bus_space_reservation_size
,
bus_space_reservation_map
,
bus_space_reservation_unmap
,
bus_space_reserve
,
bus_space_reserve_subregion
,
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_tag_create
,
bus_space_tag_destroy
,
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_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
—
#include <sys/bus.h>
bool
bus_space_handle_is_equal
(bus_space_tag_t
space, bus_space_handle_t
handle1,
bus_space_handle_t
handle2);
bool
bus_space_is_equal
(bus_space_tag_t
space1, bus_space_tag_t
space2);
void
bus_space_release
(bus_space_tag_t
t,
bus_space_reservation_t
*bsr);
int
bus_space_reserve
(bus_space_tag_t
t, bus_addr_t bpa,
bus_size_t size,
int flags,
bus_space_reservation_t
*bsrp);
int
bus_space_reserve_subregion
(bus_space_tag_t
t, 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_space_reservation_t
*bsrp);
void
bus_space_reservation_init
(bus_space_reservation_t
*bsr, bus_addr_t
addr, bus_size_t
size);
bus_size_t
bus_space_reservation_size
(bus_space_reservation_t
*bsr);
int
bus_space_reservation_map
(bus_space_tag_t
t,
bus_space_reservation_t
*bsr, int flags,
bus_space_handle_t
*bshp);
void
bus_space_reservation_unmap
(bus_space_tag_t
t, bus_space_handle_t
bsh, bus_size_t
size);
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);
void *
bus_space_vaddr
(bus_space_tag_t
space, bus_space_handle_t
handle);
paddr_t
bus_space_mmap
(bus_space_tag_t
space, bus_addr_t
addr, off_t off,
int prot,
int flags);
int
bus_space_tag_create
(bus_space_tag_t
obst, uint64_t
present, uint64_t
extpresent, const struct
bus_space_overrides *ov,
void *ctx,
bus_space_tag_t
*bstp);
void
bus_space_tag_destroy
(bus_space_tag_t
bst);
int
bus_space_peek_1
(bus_space_tag_t
space, bus_space_handle_t
handle, bus_size_t
offset, uint8_t
*datap);
int
bus_space_peek_2
(bus_space_tag_t
space, bus_space_handle_t
handle, bus_size_t
offset, uint16_t
*datap);
int
bus_space_peek_4
(bus_space_tag_t
space, bus_space_handle_t
handle, bus_size_t
offset, uint32_t
*datap);
int
bus_space_peek_8
(bus_space_tag_t
space, bus_space_handle_t
handle, bus_size_t
offset, uint64_t
*datap);
int
bus_space_poke_1
(bus_space_tag_t
space, bus_space_handle_t
handle, bus_size_t
offset, uint8_t
data);
int
bus_space_poke_2
(bus_space_tag_t
space, bus_space_handle_t
handle, bus_size_t
offset, uint16_t
data);
int
bus_space_poke_4
(bus_space_tag_t
space, bus_space_handle_t
handle, bus_size_t
offset, uint32_t
data);
int
bus_space_poke_8
(bus_space_tag_t
space, bus_space_handle_t
handle, bus_size_t
offset, uint64_t
data);
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);
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_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, const 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, const 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, const 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, const 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, const 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, const 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, const 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, const 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_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_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, const 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, const 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, const 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, const 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, const 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, const 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, const 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, const uint64_t
*datap, bus_size_t
count);
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
<sys/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_defs.h>
and in
<machine/bus_funcs.h>
to
avoid confusion with the machine-independent types and functions, and, if
possible, should be given names which make the machine-dependence clear.
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 two types of barriers: ordering barriers and completion barriers.
Ordering barriers prevent some operations from bypassing other operations. They are relatively light weight and described in terms of the operations they are intended to order. The important thing to note is that they create specific ordering constraint surrounding bus accesses but do not necessarily force any synchronization themselves. So, if there is enough distance between the memory operations being ordered, the preceding ones could complete by themselves resulting in no performance penalty.
For instance, a write before read barrier will force any writes issued before the barrier instruction to complete before any reads after the barrier are issued. This forces processors with write buffers to read data from memory rather than from the pending write in the write buffer.
Ordering barriers are usually sufficient for most circumstances, and can be combined together. For instance a read before write barrier can be combined with a write before write barrier to force all memory operations to complete before the next write is started.
Completion barriers force all memory operations and any pending exceptions to be completed before any instructions after the barrier may be issued. Completion barriers are extremely expensive and almost never required in device driver code. A single completion barrier can force the processor to stall on memory for hundreds of cycles on some machines.
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 or 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 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.
<machine/bus_defs.h>
to
facilitate use of the bus_space
functions by drivers.
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.
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.
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.
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.
The bus_space_reservation_t type is used
to describe a range of bus space. It logically consists of a
bus_addr_t, the first address in the range, and a
bus_size_t, the length in bytes of the range.
Machine-independent code creates and interrogates a
bus_space_reservation_t using a constructor,
bus_space_reservation_init
(), and accessor
functions, bus_space_reservation_addr
() and
bus_space_reservation_size
().
bus_space_is_equal
(), instead.
bus_space_map
(),
bus_space_reservation_map
(),
bus_space_reservation_unmap
(), 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
exclusively reserves and 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
This flag must have a value of 1 on all implementations for backward compatibility.
BUS_SPACE_MAP_PREFETCHABLE
bus_space_barrier
()
methods will flush the write buffer or force actual read accesses. 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
bus_space_vaddr
()
method can be used to obtain the kernel virtual address of the mapped
range. 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. Use of this mapping method is not encouraged for normal
device access; where linear access is not essential, use of the
bus_space_read/write
() methods is strongly
recommended.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_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 followed 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 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_reservation_map
(space,
bsr, flags,
handlep)The bus_space_reservation_map
()
function is similar to bus_space_map
() but it
maps a region of bus space that was previously reserved by a call to
bus_space_reserve
() or
bus_space_reserve_subregion
(). The region is
given by the space and bsr
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.
A region mapped by
bus_space_reservation_map
() may only be unmapped
by a call to bus_space_reservation_unmap
().
For more details, see the description of
bus_space_map
().
bus_space_unmap
(space,
handle, size)The bus_space_unmap
() function unmaps
and relinquishes a region of bus space reserved and 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_reservation_unmap
(space,
handle, size)The bus_space_reservation_unmap
()
function is similar to bus_space_unmap
() but it
should be called on handles mapped by
bus_space_reservation_map
() and only on such
handles. Unlike bus_space_unmap
(),
bus_space_reservation_unmap
() does not
relinquish exclusive use of the bus space named by
handle and size; that is the
job of bus_space_release
().
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 given 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.
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.
bus_space_mmap
(tag,
addr, off,
prot, flags)This method is used to provide support for memory mapping bus
space into user applications. If an address space is addressable via
volatile pointer dereferences, bus_space_mmap
()
will return the physical address (possibly encoded as a
machine-dependent cookie) of the bus space indicated by
addr and off.
addr is the base address of the device or device
region, and off is the offset into that region
that is being requested. If the request is made with
BUS_SPACE_MAP_LINEAR
as a flag, then a linear
region must be returned to the caller. If the region cannot be mapped
(either the address does not exist, or the constraints can not be met),
bus_space_mmap
() returns
-1
to indicate failure.
Note that it is not necessary that the region being requested
by a bus_space_mmap
() call be mapped into a
bus_space_handle_t.
bus_space_mmap
() is called once per
PAGE_SIZE
page in the range. The
prot argument indicates the memory protection
requested by the user application for the range.
bus_space_handle_is_equal
(space,
handle1, handle2)bus_space_handle_is_equal
() to check whether
or not handle1 and handle2
refer to regions starting at the same address in the bus space
space.bus_space_alloc
(),
bus_space_free
(),
bus_space_reserve
(),
bus_space_reserve_subregion
(), and
bus_space_release
() functions provide these
capabilities. The functions bus_space_reserve
(),
bus_space_reserve_subregion
(), and
bus_space_release
() are not yet available on all
architectures.
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_reserve
(t,
bpa, size,
flags, bsrp)The bus_space_reserve
() function
reserves, for the caller's exclusive use, size
bytes starting at the address bpa in the space
referenced by t.
bus_space_reserve
() does
not map the space. The caller should use
bus_space_reservation_map
() to map the
reservation. flags contains a hint how the caller
may map the reservation, later. Whenever possible, callers should pass
the same flags to bus_space_reserve
() as they
will pass to bus_space_reservation_map
() to map
the reservation.
On success, bus_space_reserve
()
records the reservation at bsrp and returns 0. On
failure, bsrp is undefined, and
bus_space_reserve
() returns a non-zero error
code. Possible error codes include
ENOMEM
EOPNOTSUPP
bus_space_reserve
() is not supported on this
architecture, or flags was incompatible with the
bus space represented by t.bus_space_reserve_subregion
(t,
reg_start, reg_end,
size, alignment,
boundary, flags,
bsrp)The bus_space_reserve_subregion
()
function reserves, for the caller's exclusive use,
size bytes in the space referenced by
t. The parameters reg_start,
reg_end, alignment,
boundary, and flags each
work alike to the bus_space_alloc
() parameters
of the same names.
On success,
bus_space_reserve_subregion
() records the
reservation at bsrp and returns 0. On failure,
bsrp is undefined, and
bus_space_reserve_subregion
() returns a non-zero
error code. Possible error codes include
ENOMEM
EOPNOTSUPP
bus_space_reserve
() is not supported on this
architecture, or flags was incompatible with the
bus space represented by t.bus_space_release
(t,
bsr)The bus_space_release
() function
releases the bus space bsr in
t that was previously reserved by
bus_space_reserve
() or
bus_space_reserve_subregion
().
If bus_space_release
() is called on a
reservation that has been mapped by
bus_space_reservation_map
() without subsequently
being unmapped, the behavior of the system is undefined.
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.
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.
bus_space_read_N
() and
bus_space_write_N
() family of functions is that they
provide no protection against exceptions which can occur when no physical
hardware or device responds to the read or write cycles. In such a situation,
the system typically would panic due to a kernel-mode bus error. The
bus_space_peek_N
() and
bus_space_poke_N
() family of functions provide a
mechanism to handle these exceptions gracefully without the risk of crashing
the system.
As with bus_space_read_N
() and
bus_space_write_N
(), the peek and poke functions
provide the ability to read and write 1, 2, 4, and 8 byte data items on
busses which support those access sizes. All of the constraints specified in
the descriptions of the bus_space_read_N
() and
bus_space_write_N
() functions also apply to
bus_space_peek_N
() and
bus_space_poke_N
().
In addition, explicit calls to the
bus_space_barrier
() function are not required as the
implementation will ensure all pending operations complete before the peek
or poke operation starts. The implementation will also ensure that the peek
or poke operations complete before returning.
The return value indicates the outcome of the peek or poke
operation. A return value of zero implies that a hardware device is
responding to the operation at the specified offset in the bus space. A
non-zero return value indicates that the kernel intercepted a hardware
exception (e.g., bus error) when the peek or poke operation was attempted.
Note that some busses are incapable of generating exceptions when
non-existent hardware is accessed. In such cases, these functions will
always return zero and the value of the data read by
bus_space_peek_N
() will be unspecified.
Finally, it should be noted that at this time the
bus_space_peek_N
() and
bus_space_poke_N
() functions are not re-entrant and
should not, therefore, be used from within an interrupt service routine.
This constraint may be removed at some point in the future.
bus_space_peek_1
(space,
handle, offset,
datap)bus_space_peek_2
(space,
handle, offset,
datap)bus_space_peek_4
(space,
handle, offset,
datap)bus_space_peek_8
(space,
handle, offset,
datap)The bus_space_peek_N
() family of
functions cautiously read a 1, 2, 4, or 8 byte data item from the offset
specified by offset in the region specified by
handle of the bus space specified by
space. The data item read is stored in the
location pointed to by datap. It is permissible
for datap to be NULL, in which case the data item
will be discarded after being read.
bus_space_poke_1
(space,
handle, offset,
value)bus_space_poke_2
(space,
handle, offset,
value)bus_space_poke_4
(space,
handle, offset,
value)bus_space_poke_8
(space,
handle, offset,
value)The bus_space_poke_N
() family of
functions cautiously write a 1, 2, 4, or 8 byte data item specified by
value to the offset specified by
offset in the region specified by
handle of the bus space specified by
space.
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
bus_space
operations before the
barrier to complete before any reads after the barrier may be
issued.BUS_SPACE_BARRIER_WRITE
bus_space
operations before the
barrier to complete before any writes after the barrier may be
issued.Those flags can be combined (or-ed together) to enforce ordering on different combinations of 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_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 forces 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.
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 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.
bus_space_read_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
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
(space,
handle, offset)bus_space_read_stream_2
(space,
handle, offset)bus_space_read_stream_4
(space,
handle, offset)bus_space_read_stream_8
(space,
handle, offset)bus_space_read_multi_stream_1
(space,
handle, offset,
datap, count)bus_space_read_multi_stream_2
(space,
handle, offset,
datap, count)bus_space_read_multi_stream_4
(space,
handle, offset,
datap, count)bus_space_read_multi_stream_8
(space,
handle, offset,
datap, count)bus_space_read_region_stream_1
(space,
handle, offset,
datap, count)bus_space_read_region_stream_2
(space,
handle, offset,
datap, count)bus_space_read_region_stream_4
(space,
handle, offset,
datap, count)bus_space_read_region_stream_8
(space,
handle, offset,
datap, count)bus_space_write_stream_1
(space,
handle, offset,
value)bus_space_write_stream_2
(space,
handle, offset,
value)bus_space_write_stream_4
(space,
handle, offset,
value)bus_space_write_stream_8
(space,
handle, offset,
value)bus_space_write_multi_stream_1
(space,
handle, offset,
datap, count)bus_space_write_multi_stream_2
(space,
handle, offset,
datap, count)bus_space_write_multi_stream_4
(space,
handle, offset,
datap, count)bus_space_write_multi_stream_8
(space,
handle, offset,
datap, count)bus_space_write_region_stream_1
(space,
handle, offset,
datap, count)bus_space_write_region_stream_2
(space,
handle, offset,
datap, count)bus_space_write_region_stream_4
(space,
handle, offset,
datap, count)bus_space_write_region_stream_8
(space,
handle, offset,
datap, count)These functions are defined just as their non-stream counterparts, except that they provide no byte-order translation.
bus_space_tag_create
(obst,
present, extpresent,
ov, ctx,
bstp)bus_space
calls.
ov contains function pointers
corresponding to bus_space
routines. Each
function pointer has a corresponding bit in
present or extpresent, and
if that bit is 1, the function pointer overrides the corresponding
bus_space
call for the new tag. Any combination
of these bits may be set in present:
BUS_SPACE_OVERRIDE_MAP
BUS_SPACE_OVERRIDE_UNMAP
BUS_SPACE_OVERRIDE_ALLOC
BUS_SPACE_OVERRIDE_FREE
BUS_SPACE_OVERRIDE_RESERVE
BUS_SPACE_OVERRIDE_RELEASE
BUS_SPACE_OVERRIDE_RESERVATION_MAP
BUS_SPACE_OVERRIDE_RESERVATION_UNMAP
BUS_SPACE_OVERRIDE_RESERVE_SUBREGION
bus_space_tag_create
() does not copy
ov. After a new tag is created by
bus_space_tag_create
(), ov
must not be destroyed until after the tag is destroyed by
bus_space_tag_destroy
().
The first argument of every override-function is a void *, and ctx is passed in that argument.
Return 0 if the call succeeds. Return
EOPNOTSUPP
if the architecture does not support
overrides. Return EINVAL
if
present is 0, if ov is
NULL
, or if present
indicates that an override is present, but the corresponding override in
ov is NULL
.
If the call does not succeed, *bstp is undefined.
bus_space_tag_destroy
(bst)bus_space_tag_create
(). If
bst was not created by
bus_space_tag_create
(), results are undefined. If
bst was already destroyed, results are
undefined.bus_space
functions should not yet
be considered finalized. There are several changes and improvements which
should be explored, including:
#define
in the incorrectly-written drivers.
Unfortunately, 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.bus_space
functions to userland so
that applications (such as X servers) have easier, more portable access to
device space.bus_space
functions where that is
appropriate.bus_space
functions into user space (since mapping in user space would look like it
just used a different bus-specific mapping function).bus_space
interface
specification differs slightly from the original specification that came into
wide use. A few of the function names and arguments have changed for
consistency and increased functionality. Drivers that were written to the old,
deprecated specification can be compiled by defining the
__BUS_SPACE_COMPAT_OLDDEFS
preprocessor symbol before
including <sys/bus.h>
.
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.
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.
Chris Demetriou wrote this manual page.
September 15, 2016 | NetBSD 9.0 |