355 lines
12 KiB
ReStructuredText
355 lines
12 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
=========================================
|
|
MTRR (Memory Type Range Register) control
|
|
=========================================
|
|
|
|
:Authors: - 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.rst.
|
|
|
|
.. tip::
|
|
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-shel
|
|
==============================
|
|
::
|
|
|
|
% 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 */
|