mtrr - driver for CPU memory range attributes
pseudo-device mtrr 1
The mtrr device provides access to the memory range attributes supported
by the MTRRs on Pentiums.
IOCTL INTERFACE [Toc] [Back]
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.
[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.
ioctl(2), mem(4), pctr(4), xf86(4), memconfig(8)
mtrr support was originally included in FreeBSD 3.3.
OpenBSD 3.6 November 15, 1999
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