iomap(7) Miscellaneous Information Manual iomap(7)
NAME
iomap - physical I/O address mapping
SYNOPSIS
DESCRIPTION
The mechanism allows the mapping (thus direct access) of physical I/O addresses into the user process address space. For PA-RISC machines,
the physical I/O address space begins at and extends to
The special (device) files for devices are character special files using the dynamic major number allocation scheme.
The minor number for devices is of the form:
The physical I/O address is formed by prefixing 0xAAAA with 0xF, and by appending 0x000 (this forces the I/O address to be page-aligned).
The size of the region to be mapped is given by the expression M*(2^S) 4K pages. For example, the minor number for a device starting at
that occupies 64MB is
The driver must be explicitly added to the file, the kernel rebuilt, and the system subsequently rebooted prior to first using
I/O space is always mapped with both read and write access rights, regardless of the actual permissions on the device special file.
Multiple processes can have concurrently a single device opened and mapped. It is the responsibility of the processes to synchronize their
access.
Successive calls to to map the same I/O space must be identical to the first mapping. Identical mappings have the same address and size.
Note that a process can additionally share I/O space (mapped by with a kernel driver. However, this is only possible if the driver maps in
the I/O space with user read/write access rights using the appropriate driver I/O mapping services. Any I/O space mapped by drivers with
kernel read/write access rights cannot be concurrently mapped by processes using
No or system calls are supported by the driver.
The function is used to control the device. The following requests are defined in
Map the device into user address space at the location specified by the pointer to which the third argument to points. If
the argument points to a variable containing a null pointer, the system selects an appropriate address. then
returns the user address where the device was mapped, storing it at the address pointed to by the third argument
(see below). Multiple processes can concurrently have the same device mapped.
Unmap the device from the user address space.
shuts down the file descriptor associated with the device. If the close is for the last system wide open on the device, the device is also
unmapped from the user address space; otherwise it is left mapped into the user address space (see above).
WARNINGS
Be extremely careful when creating and using devices. Inappropriate accesses to I/O devices or RAM can result in a system crash.
ERRORS
The address field was out of range,
or the request was invalid.
Not enough memory could be allocated for the mapping.
Device was already mapped and this mapping was not identical
to the initial mapping (same address, size and access rights).
Read and write calls are unsupported.
No such device at the address specified by the minor number.
Required resources for mapping could not be allocated.
Inappropriate request for this device type; fildes is not a file descriptor for an device file.
EXAMPLES
Consider the following code fragment:
...
...
where is an open file descriptor for the device special file and is the address originally requested by the program.
If is a null pointer, the system selects a suitable address then returns the selected address in addr.
If the value in addr is not a null pointer, it is used as a specified address for allocating memory. If the specified address cannot be
used, an error is returned (see
SEE ALSO
mknod(1M).
OBSOLETED iomap(7)