1Upgrading ACPI tables via initrd 2================================ 3 41) Introduction (What is this about) 52) What is this for 63) How does it work 74) References (Where to retrieve userspace tools) 8 91) What is this about 10--------------------- 11 12If the ACPI_TABLE_UPGRADE compile option is true, it is possible to 13upgrade the ACPI execution environment that is defined by the ACPI tables 14via upgrading the ACPI tables provided by the BIOS with an instrumented, 15modified, more recent version one, or installing brand new ACPI tables. 16 17For a full list of ACPI tables that can be upgraded/installed, take a look 18at the char *table_sigs[MAX_ACPI_SIGNATURE]; definition in 19drivers/acpi/tables.c. 20All ACPI tables iasl (Intel's ACPI compiler and disassembler) knows should 21be overridable, except: 22 - ACPI_SIG_RSDP (has a signature of 6 bytes) 23 - ACPI_SIG_FACS (does not have an ordinary ACPI table header) 24Both could get implemented as well. 25 26 272) What is this for 28------------------- 29 30Complain to your platform/BIOS vendor if you find a bug which is so severe 31that a workaround is not accepted in the Linux kernel. And this facility 32allows you to upgrade the buggy tables before your platform/BIOS vendor 33releases an upgraded BIOS binary. 34 35This facility can be used by platform/BIOS vendors to provide a Linux 36compatible environment without modifying the underlying platform firmware. 37 38This facility also provides a powerful feature to easily debug and test 39ACPI BIOS table compatibility with the Linux kernel by modifying old 40platform provided ACPI tables or inserting new ACPI tables. 41 42It can and should be enabled in any kernel because there is no functional 43change with not instrumented initrds. 44 45 463) How does it work 47------------------- 48 49# Extract the machine's ACPI tables: 50cd /tmp 51acpidump >acpidump 52acpixtract -a acpidump 53# Disassemble, modify and recompile them: 54iasl -d *.dat 55# For example add this statement into a _PRT (PCI Routing Table) function 56# of the DSDT: 57Store("HELLO WORLD", debug) 58# And increase the OEM Revision. For example, before modification: 59DefinitionBlock ("DSDT.aml", "DSDT", 2, "INTEL ", "TEMPLATE", 0x00000000) 60# After modification: 61DefinitionBlock ("DSDT.aml", "DSDT", 2, "INTEL ", "TEMPLATE", 0x00000001) 62iasl -sa dsdt.dsl 63# Add the raw ACPI tables to an uncompressed cpio archive. 64# They must be put into a /kernel/firmware/acpi directory inside the cpio 65# archive. Note that if the table put here matches a platform table 66# (similar Table Signature, and similar OEMID, and similar OEM Table ID) 67# with a more recent OEM Revision, the platform table will be upgraded by 68# this table. If the table put here doesn't match a platform table 69# (dissimilar Table Signature, or dissimilar OEMID, or dissimilar OEM Table 70# ID), this table will be appended. 71mkdir -p kernel/firmware/acpi 72cp dsdt.aml kernel/firmware/acpi 73# A maximum of "NR_ACPI_INITRD_TABLES (64)" tables are currently allowed 74# (see osl.c): 75iasl -sa facp.dsl 76iasl -sa ssdt1.dsl 77cp facp.aml kernel/firmware/acpi 78cp ssdt1.aml kernel/firmware/acpi 79# The uncompressed cpio archive must be the first. Other, typically 80# compressed cpio archives, must be concatenated on top of the uncompressed 81# one. Following command creates the uncompressed cpio archive and 82# concatenates the original initrd on top: 83find kernel | cpio -H newc --create > /boot/instrumented_initrd 84cat /boot/initrd >>/boot/instrumented_initrd 85# reboot with increased acpi debug level, e.g. boot params: 86acpi.debug_level=0x2 acpi.debug_layer=0xFFFFFFFF 87# and check your syslog: 88[ 1.268089] ACPI: PCI Interrupt Routing Table [\_SB_.PCI0._PRT] 89[ 1.272091] [ACPI Debug] String [0x0B] "HELLO WORLD" 90 91iasl is able to disassemble and recompile quite a lot different, 92also static ACPI tables. 93 94 954) Where to retrieve userspace tools 96------------------------------------ 97 98iasl and acpixtract are part of Intel's ACPICA project: 99http://acpica.org/ 100and should be packaged by distributions (for example in the acpica package 101on SUSE). 102 103acpidump can be found in Len Browns pmtools: 104ftp://kernel.org/pub/linux/kernel/people/lenb/acpi/utils/pmtools/acpidump 105This tool is also part of the acpica package on SUSE. 106Alternatively, used ACPI tables can be retrieved via sysfs in latest kernels: 107/sys/firmware/acpi/tables 108
