diff options
Diffstat (limited to 'Documentation/acpi/initrd_table_override.txt')
| -rw-r--r-- | Documentation/acpi/initrd_table_override.txt | 65 |
1 files changed, 39 insertions, 26 deletions
diff --git a/Documentation/acpi/initrd_table_override.txt b/Documentation/acpi/initrd_table_override.txt index 35c3f5415476..eb651a6aa285 100644 --- a/Documentation/acpi/initrd_table_override.txt +++ b/Documentation/acpi/initrd_table_override.txt @@ -1,5 +1,5 @@ -Overriding ACPI tables via initrd -================================= +Upgrading ACPI tables via initrd +================================ 1) Introduction (What is this about) 2) What is this for @@ -9,12 +9,14 @@ Overriding ACPI tables via initrd 1) What is this about --------------------- -If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible to -override nearly any ACPI table provided by the BIOS with an instrumented, -modified one. +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 overridden, take a look at -the char *table_sigs[MAX_ACPI_SIGNATURE]; definition in drivers/acpi/osl.c +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) @@ -25,17 +27,20 @@ Both could get implemented as well. 2) What is this for ------------------- -Please keep in mind that this is a debug option. -ACPI tables should not get overridden for productive use. -If BIOS ACPI tables are overridden the kernel will get tainted with the -TAINT_OVERRIDDEN_ACPI_TABLE flag. -Complain to your platform/BIOS vendor if you find a bug which is so sever -that a workaround is not accepted in the Linux kernel. +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. -Still, it can and should be enabled in any kernel, because: - - There is no functional change with not instrumented initrds - - It provides a powerful feature to easily debug and test ACPI BIOS table - compatibility with the Linux kernel. +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 @@ -50,23 +55,31 @@ 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. -# The uncompressed cpio archive must be the first. -# Other, typically compressed cpio archives, must be -# concatenated on top of the uncompressed one. +# 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: #define ACPI_OVERRIDE_TABLES 10 -# tables are currently allowed (see osl.c): +# 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 -# Create the uncompressed cpio archive and concatenate the original initrd -# on top: +# 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: |