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MTRR (Memory Type Range Register) control
17 Dec 1997
Richard Gooch
<rgooch@atnf.csiro.au>
On Intel Pentium Pro systems the Memory Type Range Registers (MTRRs)
may be used to control processor access to memory ranges. This is
most useful when you have a video (VGA) card on the PCI
bus. Enabling write-combining allows PCI write transfers to be
combined into a larger transfer before bursting over the PCI
bus. This can increase performance of image write operations 2.5
times or more.
The CONFIG_MTRR option creates a /proc/mtrr file which may be used
to manipulate your MTRRs. Typically the X server should use
this. This should have a reasonably generic interface so that
similar control registers on other processors can be easily
supported.
There are two interfaces to /proc/mtrr: one is an ASCII interface
which allows you to read and write. The other is an ioctl()
interface. The ASCII interface is meant for administration. The
ioctl() interface is meant for C programmes (i.e. the X server). The
interfaces are described below, with sample commands and C code.
===============================================================================
Reading MTRRs from the shell:
% cat /proc/mtrr
reg00: base=0x00000000 ( 0MB), size= 128MB: write-back, count=1
reg01: base=0x08000000 ( 128MB), size= 64MB: write-back, count=1
reg05: base=0x80000000 (2048MB), size= 4MB: write-combining, count=1
===============================================================================
Creating MTRRs from the shell:
% echo "base=0x80000000 size=0x400000 type=write-combining" >! /proc/mtrr
===============================================================================
Removing MTRRs from the shell:
% echo "disable=5" >! /proc/mtrr
===============================================================================
Reading MTRRs from a C programme using ioctl()'s:
/* mtrr-show.c
Source file for mtrr-show (example programme to show MTRRs using ioctl()'s)
Copyright (C) 1997 Richard Gooch
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Richard Gooch may be reached by email at rgooch@atnf.csiro.au
The postal address is:
Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia.
*/
/*
This programme will use an ioctl() on /proc/mtrr to show the current MTRR
settings. This is an alternative to reading /proc/mtrr.
Written by Richard Gooch 17-DEC-1997
Last updated by Richard Gooch 17-DEC-1997
*/
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <errno.h>
#define MTRR_NEED_STRINGS
#include <linux/mtrr.h>
#define TRUE 1
#define FALSE 0
#define ERRSTRING strerror (errno)
int main ()
{
int fd;
struct mtrr_gentry gentry;
if ( ( fd = open ("/proc/mtrr", O_RDONLY, 0) ) == -1 )
{
if (errno == ENOENT)
{
fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n",
stderr);
exit (1);
}
fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING);
exit (2);
}
for (gentry.regnum = 0; ioctl (fd, MTRRIOC_GET_ENTRY, &gentry) == 0;
++gentry.regnum)
{
if (gentry.size < 1)
{
fprintf (stderr, "Register: %u disabled\n", gentry.regnum);
continue;
}
fprintf (stderr, "Register: %u base: 0x%lx size: 0x%lx type: %s\n",
gentry.regnum, gentry.base, gentry.size,
mtrr_strings[gentry.type]);
}
if (errno == EINVAL) exit (0);
fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING);
exit (3);
} /* End Function main */
===============================================================================
Creating MTRRs from a C programme using ioctl()'s:
/* mtrr-add.c
Source file for mtrr-add (example programme to add an MTRRs using ioctl())
Copyright (C) 1997 Richard Gooch
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Richard Gooch may be reached by email at rgooch@atnf.csiro.au
The postal address is:
Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia.
*/
/*
This programme will use an ioctl() on /proc/mtrr to add an entry. The first
available mtrr is used. This is an alternative to writing /proc/mtrr.
Written by Richard Gooch 17-DEC-1997
Last updated by Richard Gooch 17-DEC-1997
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <errno.h>
#define MTRR_NEED_STRINGS
#include <linux/mtrr.h>
#define TRUE 1
#define FALSE 0
#define ERRSTRING strerror (errno)
int main (int argc, char **argv)
{
int fd;
struct mtrr_sentry sentry;
if (argc != 4)
{
fprintf (stderr, "Usage:\tmtrr-add base size type\n");
exit (1);
}
sentry.base = strtoul (argv[1], NULL, 0);
sentry.size = strtoul (argv[2], NULL, 0);
for (sentry.type = 0; sentry.type < MTRR_NUM_TYPES; ++sentry.type)
{
if (strcmp (argv[3], mtrr_strings[sentry.type]) == 0) break;
}
if (sentry.type >= MTRR_NUM_TYPES)
{
fprintf (stderr, "Illegal type: \"%s\"\n", argv[3]);
exit (2);
}
if ( ( fd = open ("/proc/mtrr", O_WRONLY, 0) ) == -1 )
{
if (errno == ENOENT)
{
fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n",
stderr);
exit (3);
}
fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING);
exit (4);
}
if (ioctl (fd, MTRRIOC_ADD_ENTRY, &sentry) == -1)
{
fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING);
exit (5);
}
fprintf (stderr, "Sleeping for 5 seconds so you can see the new entry\n");
sleep (5);
close (fd);
fputs ("I've just closed /proc/mtrr so now the new entry should be gone\n",
stderr);
} /* End Function main */
===============================================================================
|
