ACPI: update DSDT override documentation

ACPI Custom DSDT read from initramfs

2003 by Markus Gaugusch < dsdt at gaugusch dot at >

Special thanks go to Thomas Renninger from SuSE, who updated the patch for

2.6.0 and later modified it to read inside initramfs

2004 - 2008 maintained by Eric Piel < eric dot piel at tremplin-utc dot net >

This option is intended for people who would like to hack their DSDT and don't

want to recompile their kernel after every change. It can also be useful to

distros which offers pre-compiled kernels and want to allow their users to use

a modified DSDT. In the Kernel config, enable the initial RAM filesystem

support (in General Setup) and enable ACPI_CUSTOM_DSDT_INITRD at the ACPI

options (General Setup|ACPI Support|Read Custom DSDT from initramfs).

A custom DSDT (Differentiated System Description Table) is useful when your

computer uses ACPI but problems occur due to broken implementation. Typically,

your computer works but there are some troubles with the hardware detection or

the power management. You can check that troubles come from errors in the DSDT by

activating the ACPI debug option and reading the logs. This table is provided

by the BIOS, therefore it might be a good idea to check for BIOS update on your

vendor website before going any further. Errors are often caused by vendors

testing their hardware only with Windows or because there is code which is

executed only on a specific OS with a specific version and Linux hasn't been

considered during the development.

Before you run away from customising your DSDT, you should note that already

corrected tables are available for a fair amount of computers on this web-page:

http://acpi.sf.net/dsdt . Be careful though, to work correctly a DSDT has to

match closely the hardware, including the amount of RAM, the frequency of the

processor and the PCI cards present! If you are part of the unluckies who

cannot find their hardware in this database, you can modify your DSDT by

yourself. This process is less painful than it sounds. Download the Intel ASL

compiler/decompiler at http://www.intel.com/technology/IAPC/acpi/downloads.htm .

As root, you then have to dump your DSDT and decompile it. By using the

compiler messages as well as the kernel ACPI debug messages and the reference

book (available at the Intel website and also at http://www.acpi.info), it is

quite easy to obtain a fully working table.

Once your new DSDT is ready you'll have to add it to an initramfs so that the

kernel can read the table at the very beginning of the boot. As the file has to

be accessed very early during the boot process the initramfs has to be an

initramfs. The file is contained into the initramfs under the name /DSDT.aml .

To obtain such an initramfs, you might have to modify your initramfs script or

you can add it later to the initramfs with the script appended to this

document. The command will look like:

initramfs-add-dsdt initramfs.img my-dsdt.aml

In case you don't use any initramfs, the possibilities you have are to either

start using one (try mkinitrd or yaird), or use the "Include Custom DSDT"

configure option to directly include your DSDT inside the kernel.

The message "Looking for DSDT in initramfs..." will tell you if the DSDT was

found or not. If you need to update your DSDT, generate a new initramfs and

perform the steps above. Don't forget that with Lilo, you'll have to re-run it.

====================== Here starts initramfs-add-dsdt ==========================

#!/bin/bash

# Adds a DSDT file to the initrd (if it's an initramfs)

# first argument is the name of archive

# second argument is the name of the file to add

# The file will be copied as /DSDT.aml

# 20060126: fix "Premature end of file" with some old cpio (Roland Robic)

# 20060205: this time it should really work

# check the arguments

if [ $# -ne 2 ]; then

	program_name=$(basename $0)

	echo "\

$program_name: too few arguments

Usage: $program_name initrd-name.img DSDT-to-add.aml

Adds a DSDT file to an initrd (in initramfs format)

  initrd-name.img: filename of the initrd in initramfs format

  DSDT-to-add.aml: filename of the DSDT file to add

  " 1>&2

    exit 1

fi

# we should check it's an initramfs

tempcpio=$(mktemp -d)

# cleanup on exit, hangup, interrupt, quit, termination

trap 'rm -rf $tempcpio' 0 1 2 3 15

# extract the archive

gunzip -c "$1" > "$tempcpio"/initramfs.cpio || exit 1

# copy the DSDT file at the root of the directory so that we can call it "/DSDT.aml"

cp -f "$2" "$tempcpio"/DSDT.aml

# add the file

cd "$tempcpio"

(echo DSDT.aml | cpio --quiet -H newc -o -A -O "$tempcpio"/initramfs.cpio) || exit 1

cd "$OLDPWD"

# re-compress the archive

gzip -c "$tempcpio"/initramfs.cpio > "$1"

Linux supports two methods of overriding the BIOS DSDT:

CONFIG_ACPI_CUSTOM_DSDT builds the image into the kernel.

CONFIG_ACPI_CUSTOM_DSDT_INITRD adds the image to the initrd.

When to use these methods is described in detail on the

Linux/ACPI home page:

http://www.lesswatts.org/projects/acpi/overridingDSDT.php

Note that if both options are used, the DSDT supplied

by the INITRD method takes precedence.

Documentation/initramfs-add-dsdt.sh is provided for convenience

for use with the CONFIG_ACPI_CUSTOM_DSDT_INITRD method.

#!/bin/bash

# Adds a DSDT file to the initrd (if it's an initramfs)

# first argument is the name of archive

# second argument is the name of the file to add

# The file will be copied as /DSDT.aml

# 20060126: fix "Premature end of file" with some old cpio (Roland Robic)

# 20060205: this time it should really work

# check the arguments

if [ $# -ne 2 ]; then

	program_name=$(basename $0)

	echo "\

$program_name: too few arguments

Usage: $program_name initrd-name.img DSDT-to-add.aml

Adds a DSDT file to an initrd (in initramfs format)

  initrd-name.img: filename of the initrd in initramfs format

  DSDT-to-add.aml: filename of the DSDT file to add

  " 1>&2

    exit 1

fi

# we should check it's an initramfs

tempcpio=$(mktemp -d)

# cleanup on exit, hangup, interrupt, quit, termination

trap 'rm -rf $tempcpio' 0 1 2 3 15

# extract the archive

gunzip -c "$1" > "$tempcpio"/initramfs.cpio || exit 1

# copy the DSDT file at the root of the directory so that we can call it "/DSDT.aml"

cp -f "$2" "$tempcpio"/DSDT.aml

# add the file

cd "$tempcpio"

(echo DSDT.aml | cpio --quiet -H newc -o -A -O "$tempcpio"/initramfs.cpio) || exit 1

cd "$OLDPWD"

# re-compress the archive

gzip -c "$tempcpio"/initramfs.cpio > "$1"

	depends on !STANDALONE

	default n 

	help

	  This option is to load a custom ACPI DSDT

	  If you don't know what that is, say N.

	  This option supports a custom DSDT by linking it into the kernel.

	  See Documentation/acpi/dsdt-override.txt

	  If unsure, say N.

config ACPI_CUSTOM_DSDT_FILE

	string "Custom DSDT Table file to include"

	depends on BLK_DEV_INITRD

	default n

	help

	  The DSDT (Differentiated System Description Table) often needs to be

	  overridden because of broken BIOS implementations. If this feature is

	  activated you will be able to provide a customized DSDT by adding it

	  to your initramfs. If your mkinitrd tool does not support this feature

	  a script is provided in the documentation. For more details see

	  <file:Documentation/dsdt-initrd.txt> or <http://gaugusch.at/kernel.shtml>.

	  If there is no table found, it will fall-back to the custom DSDT

	  in-kernel (if activated) or to the DSDT from the BIOS.

	  Even if you do not need a new one at the moment, you may want to use a

	  better DSDT later. It is safe to say Y here.

	  This option supports a custom DSDT by optionally loading it from initrd.

	  See Documentation/acpi/dsdt-override.txt

	  If you are not using this feature now, but may use it later,

	  it is safe to say Y here.

config ACPI_BLACKLIST_YEAR

	int "Disable ACPI for systems before Jan 1st this year" if X86_32