Upgrading ACPI tables via initrd
Introduction (What is this about)
What is this for
How does it work
References (Where to retrieve userspace tools)
What is this about
If the ACPI_TABLE_UPGRADE compile option is true, it is possible to
upgrade the ACPI execution environment that is defined by the ACPI tables
via upgrading the ACPI tables provided by the BIOS with an instrumented,
modified, more recent version one, or installing brand new ACPI tables.
For a full list of ACPI tables that can be upgraded/installed, take a look
at the char *table_sigs[MAX_ACPI_SIGNATURE]; definition in
drivers/acpi/tables.c.
All ACPI tables iasl (Intel’s ACPI compiler and disassembler) knows should
be overridable, except:
- ACPI_SIG_RSDP (has a signature of 6 bytes)
- ACPI_SIG_FACS (does not have an ordinary ACPI table header)
Both could get implemented as well.
- What is this for
Complain to your platform/BIOS vendor if you find a bug which is so severe
that a workaround is not accepted in the Linux kernel. And this facility
allows you to upgrade the buggy tables before your platform/BIOS vendor
releases an upgraded BIOS binary.
This facility can be used by platform/BIOS vendors to provide a Linux
compatible environment without modifying the underlying platform firmware.
This facility also provides a powerful feature to easily debug and test
ACPI BIOS table compatibility with the Linux kernel by modifying old
platform provided ACPI tables or inserting new ACPI tables.
It can and should be enabled in any kernel because there is no functional
change with not instrumented initrds.
- How does it work
Extract the machine’s ACPI tables:
cd /tmp
acpidump >acpidump
acpixtract -a acpidump
Disassemble, modify and recompile them:
iasl -d *.dat
For example add this statement into a _PRT (PCI Routing Table) function
of the DSDT:
Store(“HELLO WORLD”, debug)
And increase the OEM Revision. For example, before modification:
DefinitionBlock (“DSDT.aml”, “DSDT”, 2, “INTEL “, “TEMPLATE”, 0x00000000)
After modification:
DefinitionBlock (“DSDT.aml”, “DSDT”, 2, “INTEL “, “TEMPLATE”, 0x00000001)
iasl -sa dsdt.dsl
Add the raw ACPI tables to an uncompressed cpio archive.
They must be put into a /kernel/firmware/acpi directory inside the cpio
archive. Note that if the table put here matches a platform table
(similar Table Signature, and similar OEMID, and similar OEM Table ID)
with a more recent OEM Revision, the platform table will be upgraded by
this table. If the table put here doesn’t match a platform table
(dissimilar Table Signature, or dissimilar OEMID, or dissimilar OEM Table
ID), this table will be appended.
mkdir -p kernel/firmware/acpi
cp dsdt.aml kernel/firmware/acpi
A maximum of “NR_ACPI_INITRD_TABLES (64)” tables are currently allowed
(see osl.c):
iasl -sa facp.dsl
iasl -sa ssdt1.dsl
cp facp.aml kernel/firmware/acpi
cp ssdt1.aml kernel/firmware/acpi
The uncompressed cpio archive must be the first. Other, typically
compressed cpio archives, must be concatenated on top of the uncompressed
one. Following command creates the uncompressed cpio archive and
concatenates the original initrd on top:
find kernel | cpio -H newc –create > /boot/instrumented_initrd
cat /boot/initrd >>/boot/instrumented_initrd
reboot with increased acpi debug level, e.g. boot params:
acpi.debug_level=0x2 acpi.debug_layer=0xFFFFFFFF
and check your syslog:
[ 1.268089] ACPI: PCI Interrupt Routing Table [_SB_.PCI0._PRT]
[ 1.272091] [ACPI Debug] String [0x0B] “HELLO WORLD”
iasl is able to disassemble and recompile quite a lot different,
also static ACPI tables.
- Where to retrieve userspace tools
iasl and acpixtract are part of Intel’s ACPICA project:
http://acpica.org/
and should be packaged by distributions (for example in the acpica package
on SUSE).
acpidump can be found in Len Browns pmtools:
ftp://kernel.org/pub/linux/kernel/people/lenb/acpi/utils/pmtools/acpidump
This tool is also part of the acpica package on SUSE.
Alternatively, used ACPI tables can be retrieved via sysfs in latest kernels:
/sys/firmware/acpi/tables
