MTRR(4) OpenBSD Programmer's Manual (i386) MTRR(4)NAMEmtrr - driver for CPU memory range attributes
SYNOPSIS
pseudo-device mtrr 1
DESCRIPTION
The mtrr device provides access to the memory range attributes supported
by the MTRRs on Pentiums.
IOCTL INTERFACE
Several architectures allow attributes to be associated with ranges of
physical memory. These attributes can be manipulated via ioctl() calls
performed on /dev/mem or /dev/xf86. Declarations and data types are to
be found in <sys/memrange.h>.
The specific attributes, and number of programmable ranges may vary
between architectures. The full set of supported attributes is:
MDF_UNCACHEABLE The region is not cached.
MDF_WRITECOMBINE Writes to the region may be combined or performed out
of order.
MDF_WRITETHROUGH Writes to the region are committed synchronously.
MDF_WRITEBACK Writes to the region are committed asynchronously.
MDF_WRITEPROTECT The region cannot be written to.
Memory ranges are described by
struct mem_range_desc {
u_int64_t mr_base; /* physical base address */
u_int64_t mr_len; /* physical length of region */
int mr_flags; /* attributes of region */
char mr_owner[8];
};
In addition to the region attributes listed above, the following flags
may also be set in the mr_flags field:
MDF_FIXBASE The region's base address cannot be changed.
MDF_FIXLEN The region's length cannot be changed.
MDF_FIRMWARE The region is believed to have been established by the
system firmware.
MDF_ACTIVE The region is currently active.
MDF_BOGUS We believe the region to be invalid or otherwise
erroneous.
MDF_FIXACTIVE The region cannot be disabled.
MDF_BUSY The region is currently owned by another process and may
not be altered.
Operations are performed using
struct mem_range_op {
struct mem_range_desc *mo_desc;
int mo_arg[2];
};
The MEMRANGE_GET ioctl is used to retrieve current memory range
attributes. If mo_arg[0] is set to 0, it will be updated with the total
number of memory range descriptors. If greater than 0, the array at
mo_desc will be filled with a corresponding number of descriptor
structures, or the maximum, whichever is less.
The MEMRANGE_SET ioctl is used to add, alter and remove memory range
attributes. A range with the MDF_FIXACTIVE flag may not be removed; a
range with the MDF_BUSY flag may not be removed or updated.
mo_arg[0] should be set to MEMRANGE_SET_UPDATE to update an existing or
establish a new range, or to MEMRANGE_SET_REMOVE to remove a range.
RETURN VALUES
[EOPNOTSUPP] Memory range operations are not supported on this
architecture.
[ENXIO] No memory range descriptors are available (e.g., firmware
has not enabled any).
[EINVAL] The memory range supplied as an argument is invalid or
overlaps another range in a fashion not supported by this
architecture.
[EBUSY] An attempt to remove or update a range failed because the
range is busy.
[ENOSPC] An attempt to create a new range failed due to a shortage
of hardware resources (e.g., descriptor slots).
[ENOENT] An attempt to remove a range failed because no range
matches the descriptor base/length supplied.
[EPERM] An attempt to remove a range failed because the range is
permanently enabled.
SEE ALSOioctl(2), mem(4), pctr(4), xf86(4), memconfig(8)HISTORYmtrr support was originally included in FreeBSD 3.3.
OpenBSD 4.9 June 16, 2008 OpenBSD 4.9
