Commit 26d14a20 authored by Changbin Du's avatar Changbin Du Committed by Jonathan Corbet
Browse files

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: default avatarChangbin Du <changbin.du@gmail.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 17156044

Documentation/x86/index.rst

+1 −0
Original line number Diff line number Diff line
@@ -16,3 +16,4 @@ x86-specific Documentation 
   earlyprintk

   zero-page

   tlb

   mtrr

Documentation/x86/mtrr.txt→Documentation/x86/mtrr.rst

+354 −0
Original line number Diff line number Diff line 
.. 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



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
@@ -23,10 +28,9 @@ 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.



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

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
@@ -54,26 +58,31 @@ For details refer to Documentation/x86/pat.txt. 
  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:



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:



Creating MTRRs from the C-shell::



  # echo "base=0xf8000000 size=0x400000 type=write-combining" >! /proc/mtrr

or if you use bash:



or if you use bash::



  # echo "base=0xf8000000 size=0x400000 type=write-combining" >| /proc/mtrr



And the result thereof:

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
@@ -82,7 +91,7 @@ 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:

typical line that you may get is::



  (--) S3: PCI: 968 rev 0, Linear FB @ 0xf8000000
@@ -91,7 +100,7 @@ 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:

know?), the following line will tell you::



  (--) S3: videoram:  4096k
@@ -100,13 +109,18 @@ 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:





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

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
@@ -117,13 +131,22 @@ 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:





Removing MTRRs from the C-shel

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

::



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

or using bash:



or using bash::



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

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

Reading MTRRs from a C program using ioctl()'s:





Reading MTRRs from a C program using ioctl()'s

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

::



  /*  mtrr-show.c
@@ -218,8 +241,11 @@ int main () 
      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:





Creating MTRRs from a C programme using ioctl()'s

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

::



  /*  mtrr-add.c
@@ -326,4 +352,3 @@ int main (int argc, char **argv) 
      fputs ("I've just closed /proc/mtrr so now the new entry should be gone\n",

      stderr);

  }   /*  End Function main  */
 
===============================================================================