Documentation/mtrr.txt - linux-mtk - Git at Google

 MTRR (Memory Type Range Register) control
 3 Jun 1999
 Richard Gooch
 <rgooch@atnf.csiro.au>

   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  */
 ===============================================================================
	MTRR (Memory Type Range Register) control
	3 Jun 1999
	Richard Gooch
	<rgooch@atnf.csiro.au>

	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 */
	===============================================================================