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Date:   Thu, 2 May 2019 13:03:17 +0800
From:   Changbin Du <changbin.du@gmail.com>
To:     Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Cc:     Changbin Du <changbin.du@gmail.com>,
        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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On Sat, Apr 27, 2019 at 02:32:13PM -0300, Mauro Carvalho Chehab wrote:
> 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
> 
Fixed.

> > +
> > +
> > +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.
>
I converted this to a 'tip' block which looks better. If have different idea, please
comment.

.. 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.
> 
> 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

-- 
Cheers,
Changbin Du