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[/] [or1k/] [trunk/] [linux/] [linux-2.4/] [Documentation/] [mtrr.txt] - Blame information for rev 1765

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1 1275 phoenix
MTRR (Memory Type Range Register) control
2
3 Jun 1999
3
Richard Gooch
4
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
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  a video (VGA) card on a PCI or AGP bus. Enabling write-combining
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  allows bus write transfers to be combined into a larger transfer
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  before bursting over the PCI/AGP bus. This can increase performance
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  of image write operations 2.5 times or more.
13
 
14
  The Cyrix 6x86, 6x86MX and M II processors have Address Range
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  Registers (ARRs) which provide a similar functionality to MTRRs. For
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  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
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  MTRRs. These are supported.  The AMD Athlon family provide 8 Intel
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  style MTRRs.
21
 
22
  The Centaur C6 (WinChip) has 8 MCRs, allowing write-combining. These
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  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
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  this. This should have a reasonably generic interface so that
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  similar control registers on other processors can be easily
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  supported.
32
 
33
 
34
There are two interfaces to /proc/mtrr: one is an ASCII interface
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which allows you to read and write. The other is an ioctl()
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interface. The ASCII interface is meant for administration. The
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ioctl() interface is meant for C programs (i.e. the X server). The
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interfaces are described below, with sample commands and C code.
39
 
40
===============================================================================
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Reading MTRRs from the shell:
42
 
43
% cat /proc/mtrr
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reg00: base=0x00000000 (   0MB), size= 128MB: write-back, count=1
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reg01: base=0x08000000 ( 128MB), size=  64MB: write-back, count=1
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===============================================================================
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Creating MTRRs from the C-shell:
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# echo "base=0xf8000000 size=0x400000 type=write-combining" >! /proc/mtrr
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or if you use bash:
50
# echo "base=0xf8000000 size=0x400000 type=write-combining" >| /proc/mtrr
51
 
52
And the result thereof:
53
% cat /proc/mtrr
54
reg00: base=0x00000000 (   0MB), size= 128MB: write-back, count=1
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reg01: base=0x08000000 ( 128MB), size=  64MB: write-back, count=1
56
reg02: base=0xf8000000 (3968MB), size=   4MB: write-combining, count=1
57
 
58
This is for video RAM at base address 0xf8000000 and size 4 megabytes. To
59
find out your base address, you need to look at the output of your X
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server, which tells you where the linear framebuffer address is. A
61
typical line that you may get is:
62
 
63
(--) S3: PCI: 968 rev 0, Linear FB @ 0xf8000000
64
 
65
Note that you should only use the value from the X server, as it may
66
move the framebuffer base address, so the only value you can trust is
67
that reported by the X server.
68
 
69
To find out the size of your framebuffer (what, you don't actually
70
know?), the following line will tell you:
71
 
72
(--) S3: videoram:  4096k
73
 
74
That's 4 megabytes, which is 0x400000 bytes (in hexadecimal).
75
A patch is being written for XFree86 which will make this automatic:
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in other words the X server will manipulate /proc/mtrr using the
77
ioctl() interface, so users won't have to do anything. If you use a
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commercial X server, lobby your vendor to add support for MTRRs.
79
===============================================================================
80
Creating 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
 
85
And the results: cat /proc/mtrr
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reg00: base=0x00000000 (   0MB), size=  64MB: write-back, count=1
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reg01: base=0xfb000000 (4016MB), size=  16MB: write-combining, count=1
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reg02: base=0xfb000000 (4016MB), size=   4kB: uncachable, count=1
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90
Some cards (especially Voodoo Graphics boards) need this 4 kB area
91
excluded from the beginning of the region because it is used for
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registers.
93
 
94
NOTE: You can only create type=uncachable region, if the first
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region that you created is type=write-combining.
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===============================================================================
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Removing MTRRs from the C-shell:
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% echo "disable=2" >! /proc/mtrr
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or using bash:
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% echo "disable=2" >| /proc/mtrr
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===============================================================================
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Reading 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 
141
#include 
142
#include 
143
#include 
144
#include 
145
#include 
146
#include 
147
#define MTRR_NEED_STRINGS
148
#include 
149
 
150
#define TRUE 1
151
#define FALSE 0
152
#define ERRSTRING strerror (errno)
153
 
154
 
155
int main ()
156
{
157
    int fd;
158
    struct mtrr_gentry gentry;
159
 
160
    if ( ( fd = open ("/proc/mtrr", O_RDONLY, 0) ) == -1 )
161
    {
162
        if (errno == ENOENT)
163
        {
164
            fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n",
165
                   stderr);
166
            exit (1);
167
        }
168
        fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING);
169
        exit (2);
170
    }
171
    for (gentry.regnum = 0; ioctl (fd, MTRRIOC_GET_ENTRY, &gentry) == 0;
172
         ++gentry.regnum)
173
    {
174
        if (gentry.size < 1)
175
        {
176
            fprintf (stderr, "Register: %u disabled\n", gentry.regnum);
177
            continue;
178
        }
179
        fprintf (stderr, "Register: %u base: 0x%lx size: 0x%lx type: %s\n",
180
                 gentry.regnum, gentry.base, gentry.size,
181
                 mtrr_strings[gentry.type]);
182
    }
183
    if (errno == EINVAL) exit (0);
184
    fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING);
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    exit (3);
186
}   /*  End Function main  */
187
===============================================================================
188
Creating MTRRs from a C programme using ioctl()'s:
189
 
190
/*  mtrr-add.c
191
 
192
    Source file for mtrr-add (example programme to add an MTRRs using ioctl())
193
 
194
    Copyright (C) 1997-1998  Richard Gooch
195
 
196
    This program is free software; you can redistribute it and/or modify
197
    it under the terms of the GNU General Public License as published by
198
    the Free Software Foundation; either version 2 of the License, or
199
    (at your option) any later version.
200
 
201
    This program is distributed in the hope that it will be useful,
202
    but WITHOUT ANY WARRANTY; without even the implied warranty of
203
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
204
    GNU General Public License for more details.
205
 
206
    You should have received a copy of the GNU General Public License
207
    along with this program; if not, write to the Free Software
208
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
209
 
210
    Richard Gooch may be reached by email at  rgooch@atnf.csiro.au
211
    The postal address is:
212
      Richard Gooch, c/o ATNF, P. O. Box 76, Epping, N.S.W., 2121, Australia.
213
*/
214
 
215
/*
216
    This programme will use an ioctl() on /proc/mtrr to add an entry. The first
217
    available mtrr is used. This is an alternative to writing /proc/mtrr.
218
 
219
 
220
    Written by      Richard Gooch   17-DEC-1997
221
 
222
    Last updated by Richard Gooch   2-MAY-1998
223
 
224
 
225
*/
226
#include 
227
#include 
228
#include 
229
#include 
230
#include 
231
#include 
232
#include 
233
#include 
234
#include 
235
#define MTRR_NEED_STRINGS
236
#include 
237
 
238
#define TRUE 1
239
#define FALSE 0
240
#define ERRSTRING strerror (errno)
241
 
242
 
243
int main (int argc, char **argv)
244
{
245
    int fd;
246
    struct mtrr_sentry sentry;
247
 
248
    if (argc != 4)
249
    {
250
        fprintf (stderr, "Usage:\tmtrr-add base size type\n");
251
        exit (1);
252
    }
253
    sentry.base = strtoul (argv[1], NULL, 0);
254
    sentry.size = strtoul (argv[2], NULL, 0);
255
    for (sentry.type = 0; sentry.type < MTRR_NUM_TYPES; ++sentry.type)
256
    {
257
        if (strcmp (argv[3], mtrr_strings[sentry.type]) == 0) break;
258
    }
259
    if (sentry.type >= MTRR_NUM_TYPES)
260
    {
261
        fprintf (stderr, "Illegal type: \"%s\"\n", argv[3]);
262
        exit (2);
263
    }
264
    if ( ( fd = open ("/proc/mtrr", O_WRONLY, 0) ) == -1 )
265
    {
266
        if (errno == ENOENT)
267
        {
268
            fputs ("/proc/mtrr not found: not supported or you don't have a PPro?\n",
269
                   stderr);
270
            exit (3);
271
        }
272
        fprintf (stderr, "Error opening /proc/mtrr\t%s\n", ERRSTRING);
273
        exit (4);
274
    }
275
    if (ioctl (fd, MTRRIOC_ADD_ENTRY, &sentry) == -1)
276
    {
277
        fprintf (stderr, "Error doing ioctl(2) on /dev/mtrr\t%s\n", ERRSTRING);
278
        exit (5);
279
    }
280
    fprintf (stderr, "Sleeping for 5 seconds so you can see the new entry\n");
281
    sleep (5);
282
    close (fd);
283
    fputs ("I've just closed /proc/mtrr so now the new entry should be gone\n",
284
           stderr);
285
}   /*  End Function main  */
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===============================================================================

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