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-MTRR (Memory Type Range Register) control
-3 Jun 1999
-Richard Gooch
-<rgooch@atnf.csiro.au>
-
- On Intel P6 family processors (Pentium Pro, Pentium II and later)
- 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 a PCI or AGP bus. Enabling write-combining
- allows bus write transfers to be combined into a larger transfer
- before bursting over the PCI/AGP bus. This can increase performance
- of image write operations 2.5 times or more.
-
- The Cyrix 6x86, 6x86MX and M II processors have Address Range
- Registers (ARRs) which provide a similar functionality to MTRRs. For
- these, the ARRs are used to emulate the MTRRs.
-
- The AMD K6-2 (stepping 8 and above) and K6-3 processors have two
- MTRRs. These are supported. The AMD Athlon family provide 8 Intel
- style MTRRs.
-
- The Centaur C6 (WinChip) has 8 MCRs, allowing write-combining. These
- are supported.
-
- The VIA Cyrix III and VIA C3 CPUs offer 8 Intel style MTRRs.
-
- 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 programs (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
-===============================================================================
-Creating MTRRs from the C-shell:
-# echo "base=0xf8000000 size=0x400000 type=write-combining" >! /proc/mtrr
-or if you use bash:
-# echo "base=0xf8000000 size=0x400000 type=write-combining" >| /proc/mtrr
-
-And the result thereof:
-% cat /proc/mtrr
-reg00: base=0x00000000 ( 0MB), size= 128MB: write-back, count=1
-reg01: base=0x08000000 ( 128MB), size= 64MB: write-back, count=1
-reg02: base=0xf8000000 (3968MB), size= 4MB: write-combining, count=1
-
-This is for video RAM at base address 0xf8000000 and size 4 megabytes. To
-find out your base address, you need to look at the output of your X
-server, which tells you where the linear framebuffer address is. A
-typical line that you may get is:
-
-(--) S3: PCI: 968 rev 0, Linear FB @ 0xf8000000
-
-Note that you should only use the value from the X server, as it may
-move the framebuffer base address, so the only value you can trust is
-that reported by the X server.
-
-To find out the size of your framebuffer (what, you don't actually
-know?), the following line will tell you:
-
-(--) S3: videoram: 4096k
-
-That's 4 megabytes, which is 0x400000 bytes (in hexadecimal).
-A patch is being written for XFree86 which will make this automatic:
-in other words the X server will manipulate /proc/mtrr using the
-ioctl() interface, so users won't have to do anything. If you use a
-commercial X server, lobby your vendor to add support for MTRRs.
-===============================================================================
-Creating overlapping MTRRs:
-
-%echo "base=0xfb000000 size=0x1000000 type=write-combining" >/proc/mtrr
-%echo "base=0xfb000000 size=0x1000 type=uncachable" >/proc/mtrr
-
-And the results: cat /proc/mtrr
-reg00: base=0x00000000 ( 0MB), size= 64MB: write-back, count=1
-reg01: base=0xfb000000 (4016MB), size= 16MB: write-combining, count=1
-reg02: base=0xfb000000 (4016MB), size= 4kB: uncachable, count=1
-
-Some cards (especially Voodoo Graphics boards) need this 4 kB area
-excluded from the beginning of the region because it is used for
-registers.
-
-NOTE: You can only create type=uncachable region, if the first
-region that you created is type=write-combining.
-===============================================================================
-Removing MTRRs from the C-shell:
-% echo "disable=2" >! /proc/mtrr
-or using bash:
-% echo "disable=2" >| /proc/mtrr
-===============================================================================
-Reading MTRRs from a C program using ioctl()'s:
-
-/* mtrr-show.c
-
- Source file for mtrr-show (example program to show MTRRs using ioctl()'s)
-
- Copyright (C) 1997-1998 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 program 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 2-MAY-1998
-
-
-*/
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <fcntl.h>
-#include <sys/ioctl.h>
-#include <errno.h>
-#include <asm/mtrr.h>
-
-#define TRUE 1
-#define FALSE 0
-#define ERRSTRING strerror (errno)
-
-static char *mtrr_strings[MTRR_NUM_TYPES] =
-{
- "uncachable", /* 0 */
- "write-combining", /* 1 */
- "?", /* 2 */
- "?", /* 3 */
- "write-through", /* 4 */
- "write-protect", /* 5 */
- "write-back", /* 6 */
-};
-
-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) 1997-1998 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 2-MAY-1998
-
-
-*/
-#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>
-#include <asm/mtrr.h>
-
-#define TRUE 1
-#define FALSE 0
-#define ERRSTRING strerror (errno)
-
-static char *mtrr_strings[MTRR_NUM_TYPES] =
-{
- "uncachable", /* 0 */
- "write-combining", /* 1 */
- "?", /* 2 */
- "?", /* 3 */
- "write-through", /* 4 */
- "write-protect", /* 5 */
- "write-back", /* 6 */
-};
-
-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 */
-===============================================================================