| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ================================ |
| Upgrading ACPI tables via initrd |
| ================================ |
| |
| 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. |
| |
| When building initrd with kernel in a single image, option |
| ACPI_TABLE_OVERRIDE_VIA_BUILTIN_INITRD should also be true for this |
| feature to work. |
| |
| 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: |
| https://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 |
