1MTRR (Memory Type Range Register) control 23 Jun 1999 3Richard Gooch 4<rgooch@atnf.csiro.au> 5 6 On Intel P6 family processors (Pentium Pro, Pentium II and later) 7 the Memory Type Range Registers (MTRRs) may be used to control 8 processor access to memory ranges. This is most useful when you have 9 a video (VGA) card on a PCI or AGP bus. Enabling write-combining 10 allows bus write transfers to be combined into a larger transfer 11 before bursting over the PCI/AGP bus. This can increase performance 12 of image write operations 2.5 times or more. 13 14 The Cyrix 6x86, 6x86MX and M II processors have Address Range 15 Registers (ARRs) which provide a similar functionality to MTRRs. For 16 these, the ARRs are used to emulate the MTRRs. 17 18 The AMD K6-2 (stepping 8 and above) and K6-3 processors have two 19 MTRRs. These are supported. The AMD Athlon family provide 8 Intel 20 style MTRRs. 21 22 The Centaur C6 (WinChip) has 8 MCRs, allowing write-combining. These 23 are supported. 24 25 The VIA Cyrix III and VIA C3 CPUs offer 8 Intel style MTRRs. 26 27 The CONFIG_MTRR option creates a /proc/mtrr file which may be used 28 to manipulate your MTRRs. Typically the X server should use 29 this. This should have a reasonably generic interface so that 30 similar control registers on other processors can be easily 31 supported. 32 33 34There are two interfaces to /proc/mtrr: one is an ASCII interface 35which allows you to read and write. The other is an ioctl() 36interface. The ASCII interface is meant for administration. The 37ioctl() interface is meant for C programs (i.e. the X server). The 38interfaces are described below, with sample commands and C code. 39 40=============================================================================== 41Reading MTRRs from the shell: 42 43% cat /proc/mtrr 44reg00: base=0x00000000 ( 0MB), size= 128MB: write-back, count=1 45reg01: base=0x08000000 ( 128MB), size= 64MB: write-back, count=1 46=============================================================================== 47Creating MTRRs from the C-shell: 48# echo "base=0xf8000000 size=0x400000 type=write-combining" >! /proc/mtrr 49or if you use bash: 50# echo "base=0xf8000000 size=0x400000 type=write-combining" >| /proc/mtrr 51 52And the result thereof: 53% cat /proc/mtrr 54reg00: base=0x00000000 ( 0MB), size= 128MB: write-back, count=1 55reg01: base=0x08000000 ( 128MB), size= 64MB: write-back, count=1 56reg02: base=0xf8000000 (3968MB), size= 4MB: write-combining, count=1 57 58This is for video RAM at base address 0xf8000000 and size 4 megabytes. To 59find out your base address, you need to look at the output of your X 60server, which tells you where the linear framebuffer address is. A 61typical line that you may get is: 62 63(--) S3: PCI: 968 rev 0, Linear FB @ 0xf8000000 64 65Note that you should only use the value from the X server, as it may 66move the framebuffer base address, so the only value you can trust is 67that reported by the X server. 68 69To find out the size of your framebuffer (what, you don't actually 70know?), the following line will tell you: 71 72(--) S3: videoram: 4096k 73 74That's 4 megabytes, which is 0x400000 bytes (in hexadecimal). 75A patch is being written for XFree86 which will make this automatic: 76in other words the X server will manipulate /proc/mtrr using the 77ioctl() interface, so users won't have to do anything. If you use a 78commercial X server, lobby your vendor to add support for MTRRs. 79=============================================================================== 80Creating overlapping MTRRs: 81 82%echo "base=0xfb000000 size=0x1000000 type=write-combining" >/proc/mtrr 83%echo "base=0xfb000000 size=0x1000 type=uncachable" >/proc/mtrr 84 85And the results: cat /proc/mtrr 86reg00: base=0x00000000 ( 0MB), size= 64MB: write-back, count=1 87reg01: base=0xfb000000 (4016MB), size= 16MB: write-combining, count=1 88reg02: base=0xfb000000 (4016MB), size= 4kB: uncachable, count=1 89 90Some cards (especially Voodoo Graphics boards) need this 4 kB area 91excluded from the beginning of the region because it is used for 92registers. 93 94NOTE: You can only create type=uncachable region, if the first 95region that you created is type=write-combining. 96=============================================================================== 97Removing MTRRs from the C-shell: 98% echo "disable=2" >! /proc/mtrr 99or using bash: 100% echo "disable=2" >| /proc/mtrr 101=============================================================================== 102Reading MTRRs from a C program using ioctl()'s: 103 104/* mtrr-show.c 105 106 Source file for mtrr-show (example program to show MTRRs using ioctl()'s) 107 108 Copyright (C) 1997-1998 Richard Gooch 109 110 This program is free software; you can redistribute it and/or modify 111 it under the terms of the GNU General Public License as published by 112 the Free Software Foundation; either version 2 of the License, or 113 (at your option) any later version. 114 115 This program is distributed in the hope that it will be useful, 116 but WITHOUT ANY WARRANTY; without even the implied warranty of 117 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 118 GNU General Public License for more details. 119 120 You should have received a copy of the GNU General Public License 121 along with this program; if not, write to the Free Software 122 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 123 124 Richard Gooch may be reached by email at rgooch@atnf.csiro.au 125 The postal address is: 126 Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia. 127*/ 128 129/* 130 This program will use an ioctl() on /proc/mtrr to show the current MTRR 131 settings. This is an alternative to reading /proc/mtrr. 132 133 134 Written by Richard Gooch 17-DEC-1997 135 136 Last updated by Richard Gooch 2-MAY-1998 137 138 139*/ 140#include <stdio.h> 141#include <stdlib.h> 142#include <string.h> 143#include <sys/types.h> 144#include <sys/stat.h> 145#include <fcntl.h> 146#include <sys/ioctl.h> 147#include <errno.h> 148#include <asm/mtrr.h> 149 150#define TRUE 1 151#define FALSE 0 152#define ERRSTRING strerror (errno) 153 154static char *mtrr_strings[MTRR_NUM_TYPES] = 155{ 156 "uncachable", /* 0 */ 157 "write-combining", /* 1 */ 158 "?", /* 2 */ 159 "?", /* 3 */ 160 "write-through", /* 4 */ 161 "write-protect", /* 5 */ 162 "write-back", /* 6 */ 163}; 164 165int main () 166{ 167 int fd; 168 struct mtrr_gentry gentry; 169 170 if ( ( fd = open ("/proc/mtrr", O_RDONLY, 0) ) == -1 ) 171 { 172 if (errno == ENOENT) 173 { 174 fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n", 175 stderr); 176 exit (1); 177 } 178 fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING); 179 exit (2); 180 } 181 for (gentry.regnum = 0; ioctl (fd, MTRRIOC_GET_ENTRY, &gentry) == 0; 182 ++gentry.regnum) 183 { 184 if (gentry.size < 1) 185 { 186 fprintf (stderr, "Register: %u disabled\n", gentry.regnum); 187 continue; 188 } 189 fprintf (stderr, "Register: %u base: 0x%lx size: 0x%lx type: %s\n", 190 gentry.regnum, gentry.base, gentry.size, 191 mtrr_strings[gentry.type]); 192 } 193 if (errno == EINVAL) exit (0); 194 fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING); 195 exit (3); 196} /* End Function main */ 197=============================================================================== 198Creating MTRRs from a C programme using ioctl()'s: 199 200/* mtrr-add.c 201 202 Source file for mtrr-add (example programme to add an MTRRs using ioctl()) 203 204 Copyright (C) 1997-1998 Richard Gooch 205 206 This program is free software; you can redistribute it and/or modify 207 it under the terms of the GNU General Public License as published by 208 the Free Software Foundation; either version 2 of the License, or 209 (at your option) any later version. 210 211 This program is distributed in the hope that it will be useful, 212 but WITHOUT ANY WARRANTY; without even the implied warranty of 213 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 214 GNU General Public License for more details. 215 216 You should have received a copy of the GNU General Public License 217 along with this program; if not, write to the Free Software 218 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 219 220 Richard Gooch may be reached by email at rgooch@atnf.csiro.au 221 The postal address is: 222 Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia. 223*/ 224 225/* 226 This programme will use an ioctl() on /proc/mtrr to add an entry. The first 227 available mtrr is used. This is an alternative to writing /proc/mtrr. 228 229 230 Written by Richard Gooch 17-DEC-1997 231 232 Last updated by Richard Gooch 2-MAY-1998 233 234 235*/ 236#include <stdio.h> 237#include <string.h> 238#include <stdlib.h> 239#include <unistd.h> 240#include <sys/types.h> 241#include <sys/stat.h> 242#include <fcntl.h> 243#include <sys/ioctl.h> 244#include <errno.h> 245#include <asm/mtrr.h> 246 247#define TRUE 1 248#define FALSE 0 249#define ERRSTRING strerror (errno) 250 251static char *mtrr_strings[MTRR_NUM_TYPES] = 252{ 253 "uncachable", /* 0 */ 254 "write-combining", /* 1 */ 255 "?", /* 2 */ 256 "?", /* 3 */ 257 "write-through", /* 4 */ 258 "write-protect", /* 5 */ 259 "write-back", /* 6 */ 260}; 261 262int main (int argc, char **argv) 263{ 264 int fd; 265 struct mtrr_sentry sentry; 266 267 if (argc != 4) 268 { 269 fprintf (stderr, "Usage:\tmtrr-add base size type\n"); 270 exit (1); 271 } 272 sentry.base = strtoul (argv[1], NULL, 0); 273 sentry.size = strtoul (argv[2], NULL, 0); 274 for (sentry.type = 0; sentry.type < MTRR_NUM_TYPES; ++sentry.type) 275 { 276 if (strcmp (argv[3], mtrr_strings[sentry.type]) == 0) break; 277 } 278 if (sentry.type >= MTRR_NUM_TYPES) 279 { 280 fprintf (stderr, "Illegal type: \"%s\"\n", argv[3]); 281 exit (2); 282 } 283 if ( ( fd = open ("/proc/mtrr", O_WRONLY, 0) ) == -1 ) 284 { 285 if (errno == ENOENT) 286 { 287 fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n", 288 stderr); 289 exit (3); 290 } 291 fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING); 292 exit (4); 293 } 294 if (ioctl (fd, MTRRIOC_ADD_ENTRY, &sentry) == -1) 295 { 296 fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING); 297 exit (5); 298 } 299 fprintf (stderr, "Sleeping for 5 seconds so you can see the new entry\n"); 300 sleep (5); 301 close (fd); 302 fputs ("I've just closed /proc/mtrr so now the new entry should be gone\n", 303 stderr); 304} /* End Function main */ 305=============================================================================== 306