[linux-2.6-block.git] / Documentation / x86 / mtrr.txt

MTRR (Memory Type Range Register) control

Richard Gooch <rgooch@atnf.csiro.au> - 3 Jun 1999
Luis R. Rodriguez <mcgrof@do-not-panic.com> - April 9, 2015

===============================================================================
Phasing out MTRR use

MTRR use is replaced on modern x86 hardware with PAT. Direct MTRR use by
drivers on Linux is now completely phased out, device drivers should use
arch_phys_wc_add() in combination with ioremap_wc() to make MTRR effective on
non-PAT systems while a no-op but equally effective on PAT enabled systems.

Even if Linux does not use MTRRs directly, some x86 platform firmware may still
set up MTRRs early before booting the OS. They do this as some platform
firmware may still have implemented access to MTRRs which would be controlled
and handled by the platform firmware directly. An example of platform use of
MTRRs is through the use of SMI handlers, one case could be for fan control,
the platform code would need uncachable access to some of its fan control
registers. Such platform access does not need any Operating System MTRR code in
place other than mtrr_type_lookup() to ensure any OS specific mapping requests
are aligned with platform MTRR setup. If MTRRs are only set up by the platform
firmware code though and the OS does not make any specific MTRR mapping
requests mtrr_type_lookup() should always return MTRR_TYPE_INVALID.

For details refer to Documentation/x86/pat.txt.

===============================================================================

  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  */
===============================================================================
Commit	Line	Data
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	===============================================================================