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#include <machine/bus.h>
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.amp; creating a non-linear register space). In some cases, a single driver may need to access the same type of device in multiple ways in a single system or architecture. The goal of the bus_space functions is to allow a single driver source file to manipulate a set of devices on different system architectures, and to allow a single driver object file to manipulate a set of devices on multiple bus types on a single architecture.
Not all buses have to implement all functions described in this document, though that is encouraged if the operations are logically supported by the bus. Unimplemented functions should cause compile-time errors if possible.
All of the interface definitions described in this document are shown as function prototypes and discussed as if they were required to be functions. Implementations are encouraged to implement prototyped (type-checked) versions of these interfaces, but may implement them as macros if appropriate. Machine-dependent types, variables, and functions should be marked clearly in <machine/bus.h> to avoid confusion with the machine-independent types and functions, and, if possible, should be given names which make the machine-dependence clear.
A range in bus space is described by a bus address and a bus size. The bus address describes the start of the range in bus space. The bus size describes the size of the range in bytes. Buses which are not byte addressable may require use of bus space ranges with appropriately aligned addresses and properly rounded sizes.
Access to regions of bus space is facilitated by use of bus space handles, which are usually created by mapping a specific range of a bus space. Handles may also be created by allocating and mapping a range of bus space, the actual location of which is picked by the implementation within bounds specified by the caller of the allocation function.
All of the bus space access functions require one bus space tag argument, at least one handle argument, and at least one offset argument (a bus size). The bus space tag specifies the space, each handle specifies a region in the space, and each offset specifies the offset into the region of the actual location(s) to be accessed. Offsets are given in bytes, though buses may impose alignment constraints. The offset used to access data relative to a given handle must be such that all of the data being accessed is in the mapped region that the handle describes. Trying to access data outside that region is an error.
Because some architectures' memory systems use buffering to improve memory and device access performance, there is a mechanism which can be used to create "barriers" in the bus space read and write stream. There are three types of barriers: read, write, and read/write. All reads started to the region before a read barrier must complete before any reads after the read barrier are started. (The analogous requirement is true for write barriers.) Read/write barriers force all reads and writes started before the barrier to complete before any reads or writes after the barrier are started. Correctly-written drivers will include all appropriate barriers, and assume only the read/write ordering imposed by the barrier operations.
People trying to write portable drivers with the bus_space functions should try to make minimal assumptions about what the system allows. In particular, they should expect that the system requires bus space addresses being accessed to be naturally aligned (i.e., base address of handle added to offset is a multiple of the access size), and that the system does alignment checking on pointers (i.e., pointer to objects being read and written must point to properly-aligned data).
The descriptions of the bus_space functions given below all assume that they are called with proper arguments. If called with invalid arguments or arguments that are out of range (e.g.amp; trying to access data outside of the region mapped when a given handle was created), undefined behaviour results. In that case, they may cause the system to halt, either intentionally (via panic) or unintentionally (by causing a fatal trap of by some other means) or may cause improper operation which is not immediately fatal. Functions which return void or which return data read from bus space (i.e., functions which do not obviously return an error code) do not fail. They could only fail if given invalid arguments, and in that case their behaviour is undefined. Functions which take a count of bytes have undefined results if the specified count is zero.
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.
The
flags
argument controls how the space is to be mapped.
Supported flags include:
bus_space_map(space, address, size, flags, handlep)
The
bus_space_map()
function maps the region of bus space named by the
space, ,, address,
and
size
arguments.
If successful, it returns zero
and fills in the bus space handle pointed to by
handlep
with the handle
that can be used to access the mapped region.
If unsuccessful,
it will return non-zero and leave the bus space handle pointed
to by
handlep
in an undefined state.
| BUS MAP_CACHEABLE | |
|
Try to map the space so that accesses can be cached and/or
prefetched by the system.
If this flag is not specified, the
implementation should map the space so that it will not be cached or
prefetched.
This flag must have a value of 1 on all implementations for backward compatibility. | |
| BUS MAP_LINEAR | Try to map the space so that its contents can be accessed linearly via normal memory access methods (e.g.amp; pointer dereferencing and structure accesses). This is useful when software wants to do direct access to a memory device, e.g.amp; a frame buffer. If this flag is specified and linear mapping is not possible, the bus_space_map() call should fail. If this flag is not specified, the system may map the space in whatever way is most convenient. |
Not all combinations of flags make sense or are supported with all spaces. For instance, BUS MAP_CACHEABLE may be meaningless when used on many systems' I/O port spaces, and on some systems BUS MAP_LINEAR without BUS MAP_CACHEABLE may never work. When the system hardware or firmware provides hints as to how spaces should be mapped (e.g.amp; 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.amp; requesting a non-cacheable mapping when the system can only provide a cacheable one) will cause the request to fail.
Some implementations may keep track of use of bus space for some or all bus spaces and refuse to allow duplicate allocations. This is encouraged for bus spaces which have no notion of slot-specific space addressing, such as ISA, and for spaces which coexist with those spaces (e.g.amp; 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.
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.amp; because of an
argument error), that indicates a software bug which should cause a
panic.
In that case,
bus_space_unmap()
will never return.
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_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.
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.
Some devices require or allow bus space to be allocated by the operating
system for device use.
When the devices no longer need the space, the
operating system should free it for use by other devices.
The
bus_space_alloc()
and
bus_space_free()
functions provide these capabilities.
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().
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.amp; 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_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.
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.
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.amp; because of an
argument error), that indicates a software bug which should cause a
panic.
In that case, they will never return.
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.amp; 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.
The flags argument controls what types of operations are to be ordered. Supported flags are:
| BUS BARRIER_READ | Synchronize read operations. |
| BUS BARRIER_WRITE | |
| Synchronize write operations. | |
Those flags can be combined (or-ed together) to enforce ordering on both read and write operations.
All of the specified type(s) of operation which are done to the region before the barrier operation are guaranteed to complete before any of the specified type(s) of operation done after the barrier.
Example: Consider a hypothetical device with two single-byte ports, one write-only input port (at offset 0) and a read-only output port (at offset 1). Operation of the device is as follows: data bytes are written to the input port, and are placed by the device on a stack, the top of which is read by reading from the output port. The sequence to correctly write two data bytes to the device then read those two data bytes back would be:
/*
* t and h are the tag and handle for the mapped device's
* space.
*/
bus_space_write_1(t, h, 0, data0);
bus_space_barrier(t, h, 0, 1, BUS BARRIER_WRITE); /* 1 */
bus_space_write_1(t, h, 0, data1);
bus_space_barrier(t, h, 0, 2,
BUS BARRIER_READ|BUS BARRIER_WRITE); /* 2 */
ndata1 = bus_space_read_1(t, h, 1);
bus_space_barrier(t, h, 1, 1, BUS BARRIER_READ); /* 3 */
ndata0 = bus_space_read_1(t, h, 1);
/* data0 == ndata0, data1 == ndata1 */
The first barrier makes sure that the first write finishes before the second write is issued, so that two writes to the input port are done in order and are not collapsed into a single write. This ensures that the data bytes are written to the device correctly and in order.
The second barrier makes sure that the writes to the output port finish before any of the reads to the input port are issued, thereby making sure that all of the writes are finished before data is read. This ensures that the first byte read from the device really is the last one that was written.
The third barrier makes sure that the first read finishes before the second read is issued, ensuring that data is read correctly and in order.
The barriers in the example above are specified to cover the absolute minimum number of bus space locations. It is correct (and often easier) to make barrier operations cover the device's whole range of bus space, that is, to specify an offset of zero and the size of the whole region.
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.
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.amp; because of an
argument error), that indicates a software bug which should cause a
panic.
In that case, they will never return.
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.amp; because of an
argument error), that indicates a software bug which should cause a
panic.
In that case, they will never return.
For portability, the starting addresses of the regions specified by the
each handle plus its respective offset should be a multiple of the size
of data items being copied.
On some systems, not obeying this
requirement may cause incorrect data to be copied, on others it may cause
a system crash.
Read and write operations done by the
bus_space_copy_region_N()
functions may be executed in any order.
They may also be executed out
of order with respect to other pending read and write operations unless
order is enforced by use of the
bus_space_barrier()
function.
There is no way to insert barriers between reads or writes of
individual bus space locations executed by the
bus_space_copy_region_N()
functions.
Overlapping copies between different subregions of a single region
of bus space are handled correctly by the
bus_space_copy_region_N()
functions.
These functions will never fail.
If they would fail (e.g.amp; because of an
argument error), that indicates a software bug which should cause a
panic.
In that case, they will never return.
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.amp; 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_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.
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.
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.
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 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.amp; because of an
argument error), that indicates a software bug which should cause a
panic.
In that case, they will never return.
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.amp; because of an
argument error), that indicates a software bug which should cause a
panic.
In that case, they will never return.
For portability, the starting address of the region specified by
handle
plus the offset should be a multiple of the size of data items being
written and the data array pointer should be properly aligned.
On some
systems, not obeying these requirements may cause incorrect data to be
written, on others it may cause a system crash.
Write operations done by the
bus_space_set_multi_N()
functions may be executed out of order with respect to other pending
read and write operations unless order is enforced by use of the
bus_space_barrier()
function.
Because the
bus_space_set_multi_N()
functions write the same bus space location multiple times, they
place an implicit write barrier between each successive write of that
bus space location.
These functions will never fail.
If they would fail (e.g.amp; 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.
bus_space_set_multi_1(space, handle, offset, value, count)
bus_space_set_multi_2(space, handle, offset, value, count)
bus_space_set_multi_4(space, handle, offset, value, count)
bus_space_set_multi_8(space, handle, offset, value, count)
The
bus_space_set_multi_N()
writes
value
into bus space at byte offset
offset
in the region specified by
handle
of the bus space specified by
space,
count
times.
The location being written must lie within the bus space
region specified by
handle.
| bus_space_read_stream_1()
bus_space_read_stream_2() bus_space_read_stream_4() bus_space_read_stream_8() bus_space_read_multi_stream_1() bus_space_read_multi_stream_2() bus_space_read_multi_stream_4() bus_space_read_multi_stream_8() bus_space_read_region_stream_1() bus_space_read_region_stream_2() bus_space_read_region_stream_4() bus_space_read_region_stream_8() bus_space_write_stream_1() bus_space_write_stream_2() bus_space_write_stream_4() bus_space_write_stream_8() bus_space_write_multi_stream_1() bus_space_write_multi_stream_2() bus_space_write_multi_stream_4() bus_space_write_multi_stream_8() bus_space_write_region_stream_1() bus_space_write_region_stream_2() bus_space_write_region_stream_4() bus_space_write_region_stream_8() bus_space_copy_region_stream_1() bus_space_copy_region_stream_2() bus_space_copy_region_stream_4() bus_space_copy_region_stream_8() bus_space_set_multi_stream_1() bus_space_set_multi_stream_2() bus_space_set_multi_stream_4() bus_space_set_multi_stream_8() bus_space_set_region_stream_1() bus_space_set_region_stream_2() bus_space_set_region_stream_4() bus_space_set_region_stream_8() | |
These functions are defined just as their non-stream counterparts, except that they provide no byte-order translation.
The manual page was then adapted to the version of the interface that FreeBSD imported for the CAM SCSI drivers, plus subsequent evolution. The FreeBSD bus_space version was imported in FreeBSD 3.0 .
Justin Gibbs ported these interfaces to FreeBSD .
Chris Demetriou wrote this manual page.
Warner Losh modified it for the FreeBSD implementation.
| BUS_SPACE (9) | January 15, 2017 |
| Main index | Section 9 | Options |
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