[deliverable/linux.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. Over time the only type
of effective MTRR that is expected to be supported will be for write-combining.
As MTRR use is phased out device drivers should use arch_phys_wc_add() to make
MTRR effective on non-PAT systems while a no-op on PAT enabled systems.

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