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Diffstat (limited to 'Documentation/acpi/initrd_table_override.txt')
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diff --git a/Documentation/acpi/initrd_table_override.txt b/Documentation/acpi/initrd_table_override.txt new file mode 100644 index 000000000..eb651a6aa --- /dev/null +++ b/Documentation/acpi/initrd_table_override.txt @@ -0,0 +1,107 @@ +Upgrading ACPI tables via initrd +================================ + +1) Introduction (What is this about) +2) What is this for +3) How does it work +4) References (Where to retrieve userspace tools) + +1) 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. + + +2) 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. + + +3) 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. + + +4) 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 |