1 .. SPDX-License-Identifier: GPL-2.0
2
3 =========================================
4 MTRR (Memory Type Range Register) control
5 =========================================
6
7 :Authors: - Richard Gooch <rgooch@atnf.csiro.au
8 - Luis R. Rodriguez <mcgrof@do-not-pa
9
10
11 Phasing out MTRR use
12 ====================
13
14 MTRR use is replaced on modern x86 hardware wi
15 drivers on Linux is now completely phased out,
16 arch_phys_wc_add() in combination with ioremap
17 non-PAT systems while a no-op but equally effe
18
19 Even if Linux does not use MTRRs directly, som
20 set up MTRRs early before booting the OS. They
21 firmware may still have implemented access to
22 and handled by the platform firmware directly.
23 MTRRs is through the use of SMI handlers, one
24 the platform code would need uncachable access
25 registers. Such platform access does not need
26 place other than mtrr_type_lookup() to ensure
27 are aligned with platform MTRR setup. If MTRRs
28 firmware code though and the OS does not make
29 requests mtrr_type_lookup() should always retu
30
31 For details refer to Documentation/arch/x86/pa
32
33 .. tip::
34 On Intel P6 family processors (Pentium Pro,
35 the Memory Type Range Registers (MTRRs) may
36 processor access to memory ranges. This is m
37 a video (VGA) card on a PCI or AGP bus. Enab
38 allows bus write transfers to be combined in
39 before bursting over the PCI/AGP bus. This c
40 of image write operations 2.5 times or more.
41
42 The Cyrix 6x86, 6x86MX and M II processors h
43 Registers (ARRs) which provide a similar fun
44 these, the ARRs are used to emulate the MTRR
45
46 The AMD K6-2 (stepping 8 and above) and K6-3
47 MTRRs. These are supported. The AMD Athlon
48 style MTRRs.
49
50 The Centaur C6 (WinChip) has 8 MCRs, allowin
51 are supported.
52
53 The VIA Cyrix III and VIA C3 CPUs offer 8 In
54
55 The CONFIG_MTRR option creates a /proc/mtrr
56 to manipulate your MTRRs. Typically the X se
57 this. This should have a reasonably generic
58 similar control registers on other processor
59 supported.
60
61 There are two interfaces to /proc/mtrr: one is
62 which allows you to read and write. The other
63 interface. The ASCII interface is meant for ad
64 ioctl() interface is meant for C programs (i.e
65 interfaces are described below, with sample co
66
67
68 Reading MTRRs from the shell
69 ============================
70 ::
71
72 % cat /proc/mtrr
73 reg00: base=0x00000000 ( 0MB), size= 128MB
74 reg01: base=0x08000000 ( 128MB), size= 64MB
75
76 Creating MTRRs from the C-shell::
77
78 # echo "base=0xf8000000 size=0x400000 type=w
79
80 or if you use bash::
81
82 # echo "base=0xf8000000 size=0x400000 type=w
83
84 And the result thereof::
85
86 % cat /proc/mtrr
87 reg00: base=0x00000000 ( 0MB), size= 128MB
88 reg01: base=0x08000000 ( 128MB), size= 64MB
89 reg02: base=0xf8000000 (3968MB), size= 4MB
90
91 This is for video RAM at base address 0xf80000
92 find out your base address, you need to look a
93 server, which tells you where the linear frame
94 typical line that you may get is::
95
96 (--) S3: PCI: 968 rev 0, Linear FB @ 0xf8000
97
98 Note that you should only use the value from t
99 move the framebuffer base address, so the only
100 that reported by the X server.
101
102 To find out the size of your framebuffer (what
103 know?), the following line will tell you::
104
105 (--) S3: videoram: 4096k
106
107 That's 4 megabytes, which is 0x400000 bytes (i
108 A patch is being written for XFree86 which wil
109 in other words the X server will manipulate /p
110 ioctl() interface, so users won't have to do a
111 commercial X server, lobby your vendor to add
112
113
114 Creating overlapping MTRRs
115 ==========================
116 ::
117
118 %echo "base=0xfb000000 size=0x1000000 type=w
119 %echo "base=0xfb000000 size=0x1000 type=unca
120
121 And the results::
122
123 % cat /proc/mtrr
124 reg00: base=0x00000000 ( 0MB), size= 64MB
125 reg01: base=0xfb000000 (4016MB), size= 16MB
126 reg02: base=0xfb000000 (4016MB), size= 4kB
127
128 Some cards (especially Voodoo Graphics boards)
129 excluded from the beginning of the region beca
130 registers.
131
132 NOTE: You can only create type=uncachable regi
133 region that you created is type=write-combinin
134
135
136 Removing MTRRs from the C-shel
137 ==============================
138 ::
139
140 % echo "disable=2" >! /proc/mtrr
141
142 or using bash::
143
144 % echo "disable=2" >| /proc/mtrr
145
146
147 Reading MTRRs from a C program using ioctl()'s
148 ==============================================
149 ::
150
151 /* mtrr-show.c
152
153 Source file for mtrr-show (example progr
154
155 Copyright (C) 1997-1998 Richard Gooch
156
157 This program is free software; you can r
158 it under the terms of the GNU General Pu
159 the Free Software Foundation; either ver
160 (at your option) any later version.
161
162 This program is distributed in the hope
163 but WITHOUT ANY WARRANTY; without even t
164 MERCHANTABILITY or FITNESS FOR A PARTICU
165 GNU General Public License for more deta
166
167 You should have received a copy of the G
168 along with this program; if not, write t
169 Foundation, Inc., 675 Mass Ave, Cambridg
170
171 Richard Gooch may be reached by email at
172 The postal address is:
173 Richard Gooch, c/o ATNF, P. O. Box 76,
174 */
175
176 /*
177 This program will use an ioctl() on /pro
178 settings. This is an alternative to read
179
180
181 Written by Richard Gooch 17-DEC-1
182
183 Last updated by Richard Gooch 2-MAY-19
184
185
186 */
187 #include <stdio.h>
188 #include <stdlib.h>
189 #include <string.h>
190 #include <sys/types.h>
191 #include <sys/stat.h>
192 #include <fcntl.h>
193 #include <sys/ioctl.h>
194 #include <errno.h>
195 #include <asm/mtrr.h>
196
197 #define TRUE 1
198 #define FALSE 0
199 #define ERRSTRING strerror (errno)
200
201 static char *mtrr_strings[MTRR_NUM_TYPES] =
202 {
203 "uncachable", /* 0 */
204 "write-combining", /* 1 */
205 "?", /* 2 */
206 "?", /* 3 */
207 "write-through", /* 4 */
208 "write-protect", /* 5 */
209 "write-back", /* 6 */
210 };
211
212 int main ()
213 {
214 int fd;
215 struct mtrr_gentry gentry;
216
217 if ( ( fd = open ("/proc/mtrr", O_RDONLY
218 {
219 if (errno == ENOENT)
220 {
221 fputs ("/proc/mtrr not found: not supp
222 stderr);
223 exit (1);
224 }
225 fprintf (stderr, "Error opening /proc/mtrr
226 exit (2);
227 }
228 for (gentry.regnum = 0; ioctl (fd, MTRRI
229 ++gentry.regnum)
230 {
231 if (gentry.size < 1)
232 {
233 fprintf (stderr, "Register: %u disable
234 continue;
235 }
236 fprintf (stderr, "Register: %u base: 0x%lx
237 gentry.regnum, gentry.base, gentry.size,
238 mtrr_strings[gentry.type]);
239 }
240 if (errno == EINVAL) exit (0);
241 fprintf (stderr, "Error doing ioctl(2) o
242 exit (3);
243 } /* End Function main */
244
245
246 Creating MTRRs from a C programme using ioctl(
247 ==============================================
248 ::
249
250 /* mtrr-add.c
251
252 Source file for mtrr-add (example progra
253
254 Copyright (C) 1997-1998 Richard Gooch
255
256 This program is free software; you can r
257 it under the terms of the GNU General Pu
258 the Free Software Foundation; either ver
259 (at your option) any later version.
260
261 This program is distributed in the hope
262 but WITHOUT ANY WARRANTY; without even t
263 MERCHANTABILITY or FITNESS FOR A PARTICU
264 GNU General Public License for more deta
265
266 You should have received a copy of the G
267 along with this program; if not, write t
268 Foundation, Inc., 675 Mass Ave, Cambridg
269
270 Richard Gooch may be reached by email at
271 The postal address is:
272 Richard Gooch, c/o ATNF, P. O. Box 76,
273 */
274
275 /*
276 This programme will use an ioctl() on /p
277 available mtrr is used. This is an alter
278
279
280 Written by Richard Gooch 17-DEC-1
281
282 Last updated by Richard Gooch 2-MAY-19
283
284
285 */
286 #include <stdio.h>
287 #include <string.h>
288 #include <stdlib.h>
289 #include <unistd.h>
290 #include <sys/types.h>
291 #include <sys/stat.h>
292 #include <fcntl.h>
293 #include <sys/ioctl.h>
294 #include <errno.h>
295 #include <asm/mtrr.h>
296
297 #define TRUE 1
298 #define FALSE 0
299 #define ERRSTRING strerror (errno)
300
301 static char *mtrr_strings[MTRR_NUM_TYPES] =
302 {
303 "uncachable", /* 0 */
304 "write-combining", /* 1 */
305 "?", /* 2 */
306 "?", /* 3 */
307 "write-through", /* 4 */
308 "write-protect", /* 5 */
309 "write-back", /* 6 */
310 };
311
312 int main (int argc, char **argv)
313 {
314 int fd;
315 struct mtrr_sentry sentry;
316
317 if (argc != 4)
318 {
319 fprintf (stderr, "Usage:\tmtrr-add base si
320 exit (1);
321 }
322 sentry.base = strtoul (argv[1], NULL, 0)
323 sentry.size = strtoul (argv[2], NULL, 0)
324 for (sentry.type = 0; sentry.type < MTRR
325 {
326 if (strcmp (argv[3], mtrr_strings[sentry.t
327 }
328 if (sentry.type >= MTRR_NUM_TYPES)
329 {
330 fprintf (stderr, "Illegal type: \"%s\"\n",
331 exit (2);
332 }
333 if ( ( fd = open ("/proc/mtrr", O_WRONLY
334 {
335 if (errno == ENOENT)
336 {
337 fputs ("/proc/mtrr not found: not supp
338 stderr);
339 exit (3);
340 }
341 fprintf (stderr, "Error opening /proc/mtrr
342 exit (4);
343 }
344 if (ioctl (fd, MTRRIOC_ADD_ENTRY, &sentr
345 {
346 fprintf (stderr, "Error doing ioctl(2) on
347 exit (5);
348 }
349 fprintf (stderr, "Sleeping for 5 seconds
350 sleep (5);
351 close (fd);
352 fputs ("I've just closed /proc/mtrr so n
353 stderr);
354 } /* End Function main */
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