From 71fc47a9adf8ee89e5c96a47222915c5485ac437 Mon Sep 17 00:00:00 2001 From: Markus Gaugusch Date: Tue, 5 Feb 2008 00:04:06 +0100 Subject: ACPI: basic initramfs DSDT override support The basics of DSDT from initramfs. In case this option is selected, populate_rootfs() is called a bit earlier to have the initramfs content available during ACPI initialization. This is a very similar path to the one available at http://gaugusch.at/kernel.shtml but with some update in the documentation, default set to No and the change of populate_rootfs() the "Jeff Mahony way" (which avoids reading the initramfs twice). Signed-off-by: Thomas Renninger Signed-off-by: Eric Piel Signed-off-by: Len Brown --- Documentation/acpi/dsdt-initrd.txt | 99 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 99 insertions(+) create mode 100644 Documentation/acpi/dsdt-initrd.txt (limited to 'Documentation/acpi') diff --git a/Documentation/acpi/dsdt-initrd.txt b/Documentation/acpi/dsdt-initrd.txt new file mode 100644 index 00000000000..736043359df --- /dev/null +++ b/Documentation/acpi/dsdt-initrd.txt @@ -0,0 +1,99 @@ +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" -- cgit v1.2.3