Documentation: x86: convert mtrr.txt to reST

This converts the plain text documentation to reStructuredText format and
add it to Sphinx TOC tree. No essential content change.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 354 insertions, 0 deletions

diff --git a/Documentation/x86/mtrr.rst b/Documentation/x86/mtrr.rst
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+.. 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 :doc:`pat`.
+
+.. 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  */