SEGMAP(9E) Driver Entry Points SEGMAP(9E)


NAME


segmap - map device memory into user space

SYNOPSIS


#include <sys/types.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/vm.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>


int prefixsegmap(dev_t dev, off_t off, struct as *asp, caddr_t *addrp,
off_t len, unsigned int prot, unsigned int maxprot, unsigned int flags,
cred_t *cred_p);


INTERFACE LEVEL


Architecture independent level 2 (DKI only).

ARGUMENTS


dev
Device whose memory is to be mapped.


off
Offset within device memory at which mapping begins.


asp
Pointer to the address space into which the device memory
should be mapped.


addrp
Pointer to the address in the address space to which the
device memory should be mapped.


len
Length (in bytes) of the memory to be mapped.


prot
A bit field that specifies the protections. Possible settings
are:

PROT_READ
Read access is desired.


PROT_WRITE
Write access is desired.


PROT_EXEC
Execute access is desired.


PROT_USER
User-level access is desired (the mapping is
being done as a result of a mmap(2) system
call).


PROT_ALL
All access is desired.


maxprot
Maximum protection flag possible for attempted mapping; the
PROT_WRITE bit may be masked out if the user opened the
special file read-only.


flags
Flags indicating type of mapping. Possible values are (other
bits may be set):

MAP_SHARED
Changes should be shared.


MAP_PRIVATE
Changes are private.


cred_p
Pointer to the user credentials structure.


DESCRIPTION


The segmap() entry point is an optional routine for character drivers
that support memory mapping. The mmap(2) system call, when applied to a
character special file, allows device memory to be mapped into user space
for direct access by the user application.


Typically, a character driver that needs to support the mmap(2) system
call supplies either an devmap(9E) entry point, or both an devmap(9E) and
a segmap() entry point routine (see the devmap(9E) reference page). If
no segmap() entry point is provided for the driver, devmap_setup(9F) is
used as a default.


A driver for a memory-mapped device would provide a segmap() entry point
if it:

o needs to maintain a separate context for each user mapping.
See devmap_setup(9F) for details.

o needs to assign device access attributes to the user mapping.


The responsibilities of a segmap() entry point are:

o Verify that the range, defined by offset and len, to be
mapped is valid for the device. Typically, this task is
performed by calling the devmap(9E) entry point. Note that if
you are using ddi_devmap_segmap(9F) or devmap_setup(9F) to set
up the mapping, it will call your devmap(9E) entry point for
you to validate the range to be mapped.

o Assign device access attributes to the mapping. See
ddi_devmap_segmap(9F), and ddi_device_acc_attr(9S) for
details.

o Set up device contexts for the user mapping if your device
requires context switching. See devmap_setup(9F) for
details.

o Perform the mapping with ddi_devmap_segmap(9F), or
devmap_setup(9F) and return the status if it fails.

RETURN VALUES


The segmap() routine should return 0 if the driver is successful in
performing the memory map of its device address space into the specified
address space.


The segmap() must return an error number on failure. For example, valid
error numbers would be ENXIO if the offset/length pair specified exceeds
the limits of the device memory, or EINVAL if the driver detects an
invalid type of mapping attempted.


If one of the mapping routines ddi_devmap_segmap() or
devmap_setup()fails, you must return the error number returned by the
respective routine.

SEE ALSO


mmap(2), devmap(9E), devmap_setup(9F), ddi_devmap_segmap(9F),
ddi_device_acc_attr(9S)


Writing Device Drivers


January 14, 1997 SEGMAP(9E)