MTRR(4)               OpenBSD Programmer's Manual (i386)               MTRR(4)

NAME
     mtrr - driver for CPU memory range attributes

SYNOPSIS
     pseudo-device mtrr

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 <memrange.h>

     The specific attributes, and number of programmable ranges may vary be-
     tween 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 erro-
                    neous.

     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 at-
     tributes.  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 struc-
     tures, or the maximum, whichever is less.

     The MEMRANGE_SET ioctl is used to add, alter and remove memory range at-
     tributes.  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 architec-
                   ture.

     [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 match-
                   es the descriptor base/length supplued.

     [EPERM]       An attempt to remove a range failed because the range is
                   permanently enabled.

SEE ALSO
     ioctl(2), mem(4), pctr(4), xf86(4), memconfig(8)

HISTORY
     mtrr support was originally included in FreeBSD 3.3.

OpenBSD 2.9                    November 15, 1999                             2
