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Date:   Sat, 27 Apr 2019 14:32:13 -0300
From:   Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
To:     Changbin Du <changbin.du@gmail.com>
Cc:     Jonathan Corbet <corbet@lwn.net>, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, x86@kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 10/27] Documentation: x86: convert mtrr.txt to reST
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Em Fri, 26 Apr 2019 23:31:33 +0800
Changbin Du <changbin.du@gmail.com> escreveu:

> 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>
> ---
>  Documentation/x86/index.rst |   1 +
>  Documentation/x86/mtrr.rst  | 350 ++++++++++++++++++++++++++++++++++++
>  Documentation/x86/mtrr.txt  | 329 ---------------------------------
>  3 files changed, 351 insertions(+), 329 deletions(-)
>  create mode 100644 Documentation/x86/mtrr.rst
>  delete mode 100644 Documentation/x86/mtrr.txt
> 
> diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst
> index fd54b859db9b..d805962a7238 100644
> --- a/Documentation/x86/index.rst
> +++ b/Documentation/x86/index.rst
> @@ -16,3 +16,4 @@ Linux x86 Support
>     earlyprintk
>     zero-page
>     tlb
> +   mtrr
> diff --git a/Documentation/x86/mtrr.rst b/Documentation/x86/mtrr.rst
> new file mode 100644
> index 000000000000..72da61022861
> --- /dev/null
> +++ b/Documentation/x86/mtrr.rst
> @@ -0,0 +1,350 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=========================================
> +MTRR (Memory Type Range Register) control
> +=========================================
> +
> +:Ahthors: - Richard Gooch <rgooch@atnf.csiro.au> - 3 Jun 1999
> +          - Luis R. Rodriguez <mcgrof@do-not-panic.com> - April 9, 2015

Typo: Authors

> +
> +
> +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:`x86/pat`.

I'm in doubt about the block below:

> +
> +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.

All the above were originally indented, and marked by an horizontal
bar (together with the next paragraph).

Perhaps the intention there were to mark them as some sort of per-CPU 
type notes.

Anyway, I would preserve the original indentation - possibly
replacing the horizontal bar using non-ReST standard:

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

By the ReST equivalent:

-------------------------------------------------------------------------------

Later, if x86 maintainers thing it is worth, they could add a note markup
before the block.

> +
> +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.

If you don't want to use a note markup, I would, at least, do:

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
> +==============================

There's also a typo above: C-shel -> C-shell...

> +::
> +
> +  % echo "disable=2" >! /proc/mtrr
> +
> +or using bash::
> +
> +  % echo "disable=2" >| /proc/mtrr


Yet, I would, instead rewrite this block as:


	Removing MTRRs
	==============

	Using C-shell::

		% echo "disable=2" >! /proc/mtrr

	or using bash::

		% echo "disable=2" >| /proc/mtrr


As it contains both csh and bash instructions there.

> +
> +
> +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  */
> diff --git a/Documentation/x86/mtrr.txt b/Documentation/x86/mtrr.txt
> deleted file mode 100644
> index dc3e703913ac..000000000000
> --- a/Documentation/x86/mtrr.txt
> +++ /dev/null
> @@ -1,329 +0,0 @@
> -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  */
> -===============================================================================


Thanks,
Mauro