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ACPI: update DSDT override documentation
Signed-off-by: Len Brown <len.brown@intel.com>
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Len Brown
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ACPI Custom DSDT read from initramfs
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2003 by Markus Gaugusch < dsdt at gaugusch dot at >
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Special thanks go to Thomas Renninger from SuSE, who updated the patch for
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2.6.0 and later modified it to read inside initramfs
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2004 - 2008 maintained by Eric Piel < eric dot piel at tremplin-utc dot net >
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This option is intended for people who would like to hack their DSDT and don't
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want to recompile their kernel after every change. It can also be useful to
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distros which offers pre-compiled kernels and want to allow their users to use
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a modified DSDT. In the Kernel config, enable the initial RAM filesystem
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support (in General Setup) and enable ACPI_CUSTOM_DSDT_INITRD at the ACPI
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options (General Setup|ACPI Support|Read Custom DSDT from initramfs).
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A custom DSDT (Differentiated System Description Table) is useful when your
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computer uses ACPI but problems occur due to broken implementation. Typically,
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your computer works but there are some troubles with the hardware detection or
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the power management. You can check that troubles come from errors in the DSDT by
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activating the ACPI debug option and reading the logs. This table is provided
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by the BIOS, therefore it might be a good idea to check for BIOS update on your
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vendor website before going any further. Errors are often caused by vendors
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testing their hardware only with Windows or because there is code which is
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executed only on a specific OS with a specific version and Linux hasn't been
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considered during the development.
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Before you run away from customising your DSDT, you should note that already
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corrected tables are available for a fair amount of computers on this web-page:
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http://acpi.sf.net/dsdt . Be careful though, to work correctly a DSDT has to
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match closely the hardware, including the amount of RAM, the frequency of the
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processor and the PCI cards present! If you are part of the unluckies who
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cannot find their hardware in this database, you can modify your DSDT by
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yourself. This process is less painful than it sounds. Download the Intel ASL
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compiler/decompiler at http://www.intel.com/technology/IAPC/acpi/downloads.htm .
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As root, you then have to dump your DSDT and decompile it. By using the
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compiler messages as well as the kernel ACPI debug messages and the reference
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book (available at the Intel website and also at http://www.acpi.info), it is
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quite easy to obtain a fully working table.
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Once your new DSDT is ready you'll have to add it to an initramfs so that the
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kernel can read the table at the very beginning of the boot. As the file has to
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be accessed very early during the boot process the initramfs has to be an
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initramfs. The file is contained into the initramfs under the name /DSDT.aml .
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To obtain such an initramfs, you might have to modify your initramfs script or
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you can add it later to the initramfs with the script appended to this
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document. The command will look like:
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initramfs-add-dsdt initramfs.img my-dsdt.aml
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In case you don't use any initramfs, the possibilities you have are to either
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start using one (try mkinitrd or yaird), or use the "Include Custom DSDT"
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configure option to directly include your DSDT inside the kernel.
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The message "Looking for DSDT in initramfs..." will tell you if the DSDT was
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found or not. If you need to update your DSDT, generate a new initramfs and
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perform the steps above. Don't forget that with Lilo, you'll have to re-run it.
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====================== Here starts initramfs-add-dsdt ==========================
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#!/bin/bash
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# Adds a DSDT file to the initrd (if it's an initramfs)
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# first argument is the name of archive
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# second argument is the name of the file to add
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# The file will be copied as /DSDT.aml
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# 20060126: fix "Premature end of file" with some old cpio (Roland Robic)
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# 20060205: this time it should really work
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# check the arguments
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if [ $# -ne 2 ]; then
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program_name=$(basename $0)
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echo "\
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$program_name: too few arguments
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Usage: $program_name initrd-name.img DSDT-to-add.aml
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Adds a DSDT file to an initrd (in initramfs format)
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initrd-name.img: filename of the initrd in initramfs format
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DSDT-to-add.aml: filename of the DSDT file to add
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" 1>&2
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exit 1
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fi
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# we should check it's an initramfs
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tempcpio=$(mktemp -d)
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# cleanup on exit, hangup, interrupt, quit, termination
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trap 'rm -rf $tempcpio' 0 1 2 3 15
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# extract the archive
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gunzip -c "$1" > "$tempcpio"/initramfs.cpio || exit 1
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# copy the DSDT file at the root of the directory so that we can call it "/DSDT.aml"
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cp -f "$2" "$tempcpio"/DSDT.aml
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# add the file
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cd "$tempcpio"
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(echo DSDT.aml | cpio --quiet -H newc -o -A -O "$tempcpio"/initramfs.cpio) || exit 1
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cd "$OLDPWD"
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# re-compress the archive
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gzip -c "$tempcpio"/initramfs.cpio > "$1"
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15
Documentation/acpi/dsdt-override.txt
Normal file
15
Documentation/acpi/dsdt-override.txt
Normal file
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Linux supports two methods of overriding the BIOS DSDT:
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CONFIG_ACPI_CUSTOM_DSDT builds the image into the kernel.
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CONFIG_ACPI_CUSTOM_DSDT_INITRD adds the image to the initrd.
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When to use these methods is described in detail on the
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Linux/ACPI home page:
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http://www.lesswatts.org/projects/acpi/overridingDSDT.php
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Note that if both options are used, the DSDT supplied
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by the INITRD method takes precedence.
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Documentation/initramfs-add-dsdt.sh is provided for convenience
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for use with the CONFIG_ACPI_CUSTOM_DSDT_INITRD method.
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43
Documentation/acpi/initramfs-add-dsdt.sh
Executable file
43
Documentation/acpi/initramfs-add-dsdt.sh
Executable file
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#!/bin/bash
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# Adds a DSDT file to the initrd (if it's an initramfs)
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# first argument is the name of archive
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# second argument is the name of the file to add
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# The file will be copied as /DSDT.aml
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# 20060126: fix "Premature end of file" with some old cpio (Roland Robic)
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# 20060205: this time it should really work
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# check the arguments
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if [ $# -ne 2 ]; then
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program_name=$(basename $0)
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echo "\
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$program_name: too few arguments
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Usage: $program_name initrd-name.img DSDT-to-add.aml
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Adds a DSDT file to an initrd (in initramfs format)
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initrd-name.img: filename of the initrd in initramfs format
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DSDT-to-add.aml: filename of the DSDT file to add
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" 1>&2
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exit 1
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fi
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# we should check it's an initramfs
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tempcpio=$(mktemp -d)
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# cleanup on exit, hangup, interrupt, quit, termination
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trap 'rm -rf $tempcpio' 0 1 2 3 15
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# extract the archive
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gunzip -c "$1" > "$tempcpio"/initramfs.cpio || exit 1
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# copy the DSDT file at the root of the directory so that we can call it "/DSDT.aml"
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cp -f "$2" "$tempcpio"/DSDT.aml
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# add the file
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cd "$tempcpio"
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(echo DSDT.aml | cpio --quiet -H newc -o -A -O "$tempcpio"/initramfs.cpio) || exit 1
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cd "$OLDPWD"
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# re-compress the archive
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gzip -c "$tempcpio"/initramfs.cpio > "$1"
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@ -263,8 +263,10 @@ config ACPI_CUSTOM_DSDT
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depends on !STANDALONE
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default n
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help
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This option is to load a custom ACPI DSDT
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If you don't know what that is, say N.
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This option supports a custom DSDT by linking it into the kernel.
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See Documentation/acpi/dsdt-override.txt
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If unsure, say N.
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config ACPI_CUSTOM_DSDT_FILE
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string "Custom DSDT Table file to include"
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@ -279,17 +281,11 @@ config ACPI_CUSTOM_DSDT_INITRD
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depends on BLK_DEV_INITRD
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default n
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help
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The DSDT (Differentiated System Description Table) often needs to be
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overridden because of broken BIOS implementations. If this feature is
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activated you will be able to provide a customized DSDT by adding it
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to your initramfs. If your mkinitrd tool does not support this feature
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a script is provided in the documentation. For more details see
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<file:Documentation/dsdt-initrd.txt> or <http://gaugusch.at/kernel.shtml>.
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If there is no table found, it will fall-back to the custom DSDT
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in-kernel (if activated) or to the DSDT from the BIOS.
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This option supports a custom DSDT by optionally loading it from initrd.
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See Documentation/acpi/dsdt-override.txt
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Even if you do not need a new one at the moment, you may want to use a
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better DSDT later. It is safe to say Y here.
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If you are not using this feature now, but may use it later,
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it is safe to say Y here.
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config ACPI_BLACKLIST_YEAR
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int "Disable ACPI for systems before Jan 1st this year" if X86_32
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