Commit | Line | Data |
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1da177e4 | 1 | MTRR (Memory Type Range Register) control |
2f9e8973 LR |
2 | |
3 | Richard Gooch <rgooch@atnf.csiro.au> - 3 Jun 1999 | |
4 | Luis R. Rodriguez <mcgrof@do-not-panic.com> - April 9, 2015 | |
5 | ||
6 | =============================================================================== | |
7 | Phasing out MTRR use | |
8 | ||
2baa891e LR |
9 | MTRR use is replaced on modern x86 hardware with PAT. Direct MTRR use by |
10 | drivers on Linux is now completely phased out, device drivers should use | |
11 | arch_phys_wc_add() in combination with ioremap_wc() to make MTRR effective on | |
12 | non-PAT systems while a no-op but equally effective on PAT enabled systems. | |
13 | ||
14 | Even if Linux does not use MTRRs directly, some x86 platform firmware may still | |
15 | set up MTRRs early before booting the OS. They do this as some platform | |
16 | firmware may still have implemented access to MTRRs which would be controlled | |
17 | and handled by the platform firmware directly. An example of platform use of | |
18 | MTRRs is through the use of SMI handlers, one case could be for fan control, | |
19 | the platform code would need uncachable access to some of its fan control | |
20 | registers. Such platform access does not need any Operating System MTRR code in | |
21 | place other than mtrr_type_lookup() to ensure any OS specific mapping requests | |
22 | are aligned with platform MTRR setup. If MTRRs are only set up by the platform | |
23 | firmware code though and the OS does not make any specific MTRR mapping | |
24 | requests mtrr_type_lookup() should always return MTRR_TYPE_INVALID. | |
2f9e8973 LR |
25 | |
26 | For details refer to Documentation/x86/pat.txt. | |
27 | ||
28 | =============================================================================== | |
1da177e4 LT |
29 | |
30 | On Intel P6 family processors (Pentium Pro, Pentium II and later) | |
31 | the Memory Type Range Registers (MTRRs) may be used to control | |
32 | processor access to memory ranges. This is most useful when you have | |
33 | a video (VGA) card on a PCI or AGP bus. Enabling write-combining | |
34 | allows bus write transfers to be combined into a larger transfer | |
35 | before bursting over the PCI/AGP bus. This can increase performance | |
36 | of image write operations 2.5 times or more. | |
37 | ||
38 | The Cyrix 6x86, 6x86MX and M II processors have Address Range | |
39 | Registers (ARRs) which provide a similar functionality to MTRRs. For | |
40 | these, the ARRs are used to emulate the MTRRs. | |
41 | ||
42 | The AMD K6-2 (stepping 8 and above) and K6-3 processors have two | |
43 | MTRRs. These are supported. The AMD Athlon family provide 8 Intel | |
44 | style MTRRs. | |
7225e751 | 45 | |
1da177e4 LT |
46 | The Centaur C6 (WinChip) has 8 MCRs, allowing write-combining. These |
47 | are supported. | |
48 | ||
49 | The VIA Cyrix III and VIA C3 CPUs offer 8 Intel style MTRRs. | |
50 | ||
51 | The CONFIG_MTRR option creates a /proc/mtrr file which may be used | |
52 | to manipulate your MTRRs. Typically the X server should use | |
53 | this. This should have a reasonably generic interface so that | |
54 | similar control registers on other processors can be easily | |
55 | supported. | |
56 | ||
57 | ||
58 | There are two interfaces to /proc/mtrr: one is an ASCII interface | |
59 | which allows you to read and write. The other is an ioctl() | |
60 | interface. The ASCII interface is meant for administration. The | |
61 | ioctl() interface is meant for C programs (i.e. the X server). The | |
62 | interfaces are described below, with sample commands and C code. | |
63 | ||
64 | =============================================================================== | |
65 | Reading MTRRs from the shell: | |
66 | ||
67 | % cat /proc/mtrr | |
68 | reg00: base=0x00000000 ( 0MB), size= 128MB: write-back, count=1 | |
69 | reg01: base=0x08000000 ( 128MB), size= 64MB: write-back, count=1 | |
70 | =============================================================================== | |
71 | Creating MTRRs from the C-shell: | |
72 | # echo "base=0xf8000000 size=0x400000 type=write-combining" >! /proc/mtrr | |
73 | or if you use bash: | |
74 | # echo "base=0xf8000000 size=0x400000 type=write-combining" >| /proc/mtrr | |
75 | ||
76 | And the result thereof: | |
77 | % cat /proc/mtrr | |
78 | reg00: base=0x00000000 ( 0MB), size= 128MB: write-back, count=1 | |
79 | reg01: base=0x08000000 ( 128MB), size= 64MB: write-back, count=1 | |
80 | reg02: base=0xf8000000 (3968MB), size= 4MB: write-combining, count=1 | |
81 | ||
82 | This is for video RAM at base address 0xf8000000 and size 4 megabytes. To | |
83 | find out your base address, you need to look at the output of your X | |
84 | server, which tells you where the linear framebuffer address is. A | |
85 | typical line that you may get is: | |
86 | ||
87 | (--) S3: PCI: 968 rev 0, Linear FB @ 0xf8000000 | |
88 | ||
89 | Note that you should only use the value from the X server, as it may | |
90 | move the framebuffer base address, so the only value you can trust is | |
91 | that reported by the X server. | |
92 | ||
93 | To find out the size of your framebuffer (what, you don't actually | |
94 | know?), the following line will tell you: | |
95 | ||
96 | (--) S3: videoram: 4096k | |
97 | ||
98 | That's 4 megabytes, which is 0x400000 bytes (in hexadecimal). | |
99 | A patch is being written for XFree86 which will make this automatic: | |
100 | in other words the X server will manipulate /proc/mtrr using the | |
101 | ioctl() interface, so users won't have to do anything. If you use a | |
102 | commercial X server, lobby your vendor to add support for MTRRs. | |
103 | =============================================================================== | |
104 | Creating overlapping MTRRs: | |
105 | ||
106 | %echo "base=0xfb000000 size=0x1000000 type=write-combining" >/proc/mtrr | |
107 | %echo "base=0xfb000000 size=0x1000 type=uncachable" >/proc/mtrr | |
108 | ||
109 | And the results: cat /proc/mtrr | |
110 | reg00: base=0x00000000 ( 0MB), size= 64MB: write-back, count=1 | |
111 | reg01: base=0xfb000000 (4016MB), size= 16MB: write-combining, count=1 | |
112 | reg02: base=0xfb000000 (4016MB), size= 4kB: uncachable, count=1 | |
113 | ||
7225e751 | 114 | Some cards (especially Voodoo Graphics boards) need this 4 kB area |
1da177e4 LT |
115 | excluded from the beginning of the region because it is used for |
116 | registers. | |
117 | ||
118 | NOTE: You can only create type=uncachable region, if the first | |
119 | region that you created is type=write-combining. | |
120 | =============================================================================== | |
121 | Removing MTRRs from the C-shell: | |
122 | % echo "disable=2" >! /proc/mtrr | |
123 | or using bash: | |
124 | % echo "disable=2" >| /proc/mtrr | |
125 | =============================================================================== | |
126 | Reading MTRRs from a C program using ioctl()'s: | |
127 | ||
128 | /* mtrr-show.c | |
129 | ||
130 | Source file for mtrr-show (example program to show MTRRs using ioctl()'s) | |
131 | ||
132 | Copyright (C) 1997-1998 Richard Gooch | |
133 | ||
134 | This program is free software; you can redistribute it and/or modify | |
135 | it under the terms of the GNU General Public License as published by | |
136 | the Free Software Foundation; either version 2 of the License, or | |
137 | (at your option) any later version. | |
138 | ||
139 | This program is distributed in the hope that it will be useful, | |
140 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
141 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
142 | GNU General Public License for more details. | |
143 | ||
144 | You should have received a copy of the GNU General Public License | |
145 | along with this program; if not, write to the Free Software | |
146 | Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. | |
147 | ||
148 | Richard Gooch may be reached by email at rgooch@atnf.csiro.au | |
149 | The postal address is: | |
150 | Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia. | |
151 | */ | |
152 | ||
153 | /* | |
154 | This program will use an ioctl() on /proc/mtrr to show the current MTRR | |
155 | settings. This is an alternative to reading /proc/mtrr. | |
156 | ||
157 | ||
158 | Written by Richard Gooch 17-DEC-1997 | |
159 | ||
160 | Last updated by Richard Gooch 2-MAY-1998 | |
161 | ||
162 | ||
163 | */ | |
164 | #include <stdio.h> | |
235963b2 | 165 | #include <stdlib.h> |
1da177e4 LT |
166 | #include <string.h> |
167 | #include <sys/types.h> | |
168 | #include <sys/stat.h> | |
169 | #include <fcntl.h> | |
170 | #include <sys/ioctl.h> | |
171 | #include <errno.h> | |
1da177e4 LT |
172 | #include <asm/mtrr.h> |
173 | ||
174 | #define TRUE 1 | |
175 | #define FALSE 0 | |
176 | #define ERRSTRING strerror (errno) | |
177 | ||
235963b2 RD |
178 | static char *mtrr_strings[MTRR_NUM_TYPES] = |
179 | { | |
180 | "uncachable", /* 0 */ | |
181 | "write-combining", /* 1 */ | |
182 | "?", /* 2 */ | |
183 | "?", /* 3 */ | |
184 | "write-through", /* 4 */ | |
185 | "write-protect", /* 5 */ | |
186 | "write-back", /* 6 */ | |
187 | }; | |
1da177e4 LT |
188 | |
189 | int main () | |
190 | { | |
191 | int fd; | |
192 | struct mtrr_gentry gentry; | |
193 | ||
194 | if ( ( fd = open ("/proc/mtrr", O_RDONLY, 0) ) == -1 ) | |
195 | { | |
196 | if (errno == ENOENT) | |
197 | { | |
198 | fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n", | |
199 | stderr); | |
200 | exit (1); | |
201 | } | |
202 | fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING); | |
203 | exit (2); | |
204 | } | |
205 | for (gentry.regnum = 0; ioctl (fd, MTRRIOC_GET_ENTRY, &gentry) == 0; | |
206 | ++gentry.regnum) | |
207 | { | |
208 | if (gentry.size < 1) | |
209 | { | |
210 | fprintf (stderr, "Register: %u disabled\n", gentry.regnum); | |
211 | continue; | |
212 | } | |
213 | fprintf (stderr, "Register: %u base: 0x%lx size: 0x%lx type: %s\n", | |
214 | gentry.regnum, gentry.base, gentry.size, | |
215 | mtrr_strings[gentry.type]); | |
216 | } | |
217 | if (errno == EINVAL) exit (0); | |
218 | fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING); | |
219 | exit (3); | |
220 | } /* End Function main */ | |
221 | =============================================================================== | |
222 | Creating MTRRs from a C programme using ioctl()'s: | |
223 | ||
224 | /* mtrr-add.c | |
225 | ||
226 | Source file for mtrr-add (example programme to add an MTRRs using ioctl()) | |
227 | ||
228 | Copyright (C) 1997-1998 Richard Gooch | |
229 | ||
230 | This program is free software; you can redistribute it and/or modify | |
231 | it under the terms of the GNU General Public License as published by | |
232 | the Free Software Foundation; either version 2 of the License, or | |
233 | (at your option) any later version. | |
234 | ||
235 | This program is distributed in the hope that it will be useful, | |
236 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
237 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
238 | GNU General Public License for more details. | |
239 | ||
240 | You should have received a copy of the GNU General Public License | |
241 | along with this program; if not, write to the Free Software | |
242 | Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. | |
243 | ||
244 | Richard Gooch may be reached by email at rgooch@atnf.csiro.au | |
245 | The postal address is: | |
246 | Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia. | |
247 | */ | |
248 | ||
249 | /* | |
250 | This programme will use an ioctl() on /proc/mtrr to add an entry. The first | |
251 | available mtrr is used. This is an alternative to writing /proc/mtrr. | |
252 | ||
253 | ||
254 | Written by Richard Gooch 17-DEC-1997 | |
255 | ||
256 | Last updated by Richard Gooch 2-MAY-1998 | |
257 | ||
258 | ||
259 | */ | |
260 | #include <stdio.h> | |
261 | #include <string.h> | |
262 | #include <stdlib.h> | |
263 | #include <unistd.h> | |
264 | #include <sys/types.h> | |
265 | #include <sys/stat.h> | |
266 | #include <fcntl.h> | |
267 | #include <sys/ioctl.h> | |
268 | #include <errno.h> | |
1da177e4 LT |
269 | #include <asm/mtrr.h> |
270 | ||
271 | #define TRUE 1 | |
272 | #define FALSE 0 | |
273 | #define ERRSTRING strerror (errno) | |
274 | ||
235963b2 RD |
275 | static char *mtrr_strings[MTRR_NUM_TYPES] = |
276 | { | |
277 | "uncachable", /* 0 */ | |
278 | "write-combining", /* 1 */ | |
279 | "?", /* 2 */ | |
280 | "?", /* 3 */ | |
281 | "write-through", /* 4 */ | |
282 | "write-protect", /* 5 */ | |
283 | "write-back", /* 6 */ | |
284 | }; | |
1da177e4 LT |
285 | |
286 | int main (int argc, char **argv) | |
287 | { | |
288 | int fd; | |
289 | struct mtrr_sentry sentry; | |
290 | ||
291 | if (argc != 4) | |
292 | { | |
293 | fprintf (stderr, "Usage:\tmtrr-add base size type\n"); | |
294 | exit (1); | |
295 | } | |
296 | sentry.base = strtoul (argv[1], NULL, 0); | |
297 | sentry.size = strtoul (argv[2], NULL, 0); | |
298 | for (sentry.type = 0; sentry.type < MTRR_NUM_TYPES; ++sentry.type) | |
299 | { | |
300 | if (strcmp (argv[3], mtrr_strings[sentry.type]) == 0) break; | |
301 | } | |
302 | if (sentry.type >= MTRR_NUM_TYPES) | |
303 | { | |
304 | fprintf (stderr, "Illegal type: \"%s\"\n", argv[3]); | |
305 | exit (2); | |
306 | } | |
307 | if ( ( fd = open ("/proc/mtrr", O_WRONLY, 0) ) == -1 ) | |
308 | { | |
309 | if (errno == ENOENT) | |
310 | { | |
311 | fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n", | |
312 | stderr); | |
313 | exit (3); | |
314 | } | |
315 | fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING); | |
316 | exit (4); | |
317 | } | |
318 | if (ioctl (fd, MTRRIOC_ADD_ENTRY, &sentry) == -1) | |
319 | { | |
320 | fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING); | |
321 | exit (5); | |
322 | } | |
323 | fprintf (stderr, "Sleeping for 5 seconds so you can see the new entry\n"); | |
324 | sleep (5); | |
325 | close (fd); | |
326 | fputs ("I've just closed /proc/mtrr so now the new entry should be gone\n", | |
327 | stderr); | |
328 | } /* End Function main */ | |
329 | =============================================================================== |