Allow custom DSDT overrides in grub per default

[Egon A. Rath]

For some PC models it's necessary to use a custom ACPI DSDT Table for the correct working of Fans and other system stuff. To load such a table you could either compile a new kernel with this custom table in it, or provide it via grub.

It would be a huge benefit for Ubuntu to provide this functionality out of the box.

Current steps necessary:
=====================

1.) Build a new DSDT and place it under /boot/dsdt.aml
2.) Place the following content under /etc/grub.d/01_acpi:

--------------------CUT--------------------
#! /bin/sh -e

# Uncomment to load custom ACPI table
GRUB_CUSTOM_ACPI="/boot/dsdt.aml"

# DON'T MODIFY ANYTHING BELOW THIS LINE!

prefix=/usr
exec_prefix=${prefix}
libdir=${exec_prefix}/lib

. ${libdir}/grub/grub-mkconfig_lib

# Load custom ACPI table
if [ x${GRUB_CUSTOM_ACPI} != x ] && [ -f ${GRUB_CUSTOM_ACPI} ] \
        && is_path_readable_by_grub ${GRUB_CUSTOM_ACPI}; then
    echo "Found custom ACPI table: ${GRUB_CUSTOM_ACPI}" >&2
    prepare_grub_to_access_device `${grub_probe} --target=device ${GRUB_CUSTOM_ACPI}` | sed -e "s/^/ /"
    cat << EOF
acpi (\$root)`make_system_path_relative_to_its_root ${GRUB_CUSTOM_ACPI}`
EOF
fi
--------------------CUT--------------------
3.) update-grub

Desired steps necessary:
=====================

1.) Ship the above (or a similar) script fragment per default
2.) Place the GRUB_CUSTOM_ACPU in /etc/default/grub for centralised access

Additional information
==================

Ubuntu-release:
    Description: Ubuntu 12.04.1 LTS
    Release: 12.04

grub-packages:
grub2:
  Installed: (none)
  Candidate: 1.99-21ubuntu3.1
  Version table:
     1.99-21ubuntu3.1 0
        500 http://susrtumi1/ubuntu/ubuntu/ precise-updates/universe i386 Packages
     1.99-21ubuntu3 0
        500 http://susrtumi1/ubuntu/ubuntu/ precise/universe i386 Packages
test@test01:/etc/default$ dpkg --list | grep grub
ii grub-common 1.99-21ubuntu3.1 GRand Unified Bootloader (common files)
ii grub-gfxpayload-lists 0.6 GRUB gfxpayload blacklist
ii grub-pc 1.99-21ubuntu3.1 GRand Unified Bootloader, version 2 (PC/BIOS version)
ii grub-pc-bin 1.99-21ubuntu3.1 GRand Unified Bootloader, version 2 (PC/BIOS binaries)
ii grub2-common 1.99-21ubuntu3.1 GRand Unified Bootloader (common files for version 2)

[Peter Meiser (meiser79)]

Looking at the current initramfs-tools package, you can put a DSDT.aml into /etc/initramfs-tools/ so that it gets used.

[Phillip Susi (psusi)]

Support for loading a DSDT from the initramfs was removed from the kernel some time ago. It has to be passed by the boot loader now.

[Peter Meiser (meiser79)]

Ok, thanks. I'm just trying it with my old Samsung P35. How do I know that the DSDT was loaded successfully? I can't see any hints in dmesg.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Ryan C. Underwood (nemesis-icequake)]

GRUB also accepts an 'acpi' command:
https://www.gnu.org/software/grub/manual/html_node/acpi.html

Perhaps we could just make it easier for that command to be generated as a part of boot entry blocks in grub.cfg.

[jacobS (jacsalomon)]

This is not for grub only, they need to re-compile kernel with config flag enabled:

# CONFIG_ACPI_CUSTOM_DSDT is not set

+ CONFIG_ACPI_CUSTOM_DSDT = y

Is recommend to enabled this in all generic-kernel versions, otherwise they do not override DSDT bogus tables

[Ryan C. Underwood (nemesis-icequake)]

No @jacsalomon, that's not true. If you override via grub, there's no need for the kernel override.
That is, this scheme works with Ubuntu's kernel configuration:
CONFIG_ACPI_CUSTOM_DSDT_FILE=""
# CONFIG_ACPI_CUSTOM_DSDT is not set