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Documentation / acpi / initrd_table_override.txt

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Based on kernel version 4.7.2. Page generated on 2016-08-22 22:39 EST.

1	Upgrading ACPI tables via initrd
2	================================
4	1) Introduction (What is this about)
5	2) What is this for
6	3) How does it work
7	4) References (Where to retrieve userspace tools)
9	1) What is this about
10	---------------------
12	If the ACPI_TABLE_UPGRADE compile option is true, it is possible to
13	upgrade the ACPI execution environment that is defined by the ACPI tables
14	via upgrading the ACPI tables provided by the BIOS with an instrumented,
15	modified, more recent version one, or installing brand new ACPI tables.
17	For a full list of ACPI tables that can be upgraded/installed, take a look
18	at the char *table_sigs[MAX_ACPI_SIGNATURE]; definition in
19	drivers/acpi/tables.c.
20	All ACPI tables iasl (Intel's ACPI compiler and disassembler) knows should
21	be overridable, except:
22	   - ACPI_SIG_RSDP (has a signature of 6 bytes)
23	   - ACPI_SIG_FACS (does not have an ordinary ACPI table header)
24	Both could get implemented as well.
27	2) What is this for
28	-------------------
30	Complain to your platform/BIOS vendor if you find a bug which is so severe
31	that a workaround is not accepted in the Linux kernel. And this facility
32	allows you to upgrade the buggy tables before your platform/BIOS vendor
33	releases an upgraded BIOS binary.
35	This facility can be used by platform/BIOS vendors to provide a Linux
36	compatible environment without modifying the underlying platform firmware.
38	This facility also provides a powerful feature to easily debug and test
39	ACPI BIOS table compatibility with the Linux kernel by modifying old
40	platform provided ACPI tables or inserting new ACPI tables.
42	It can and should be enabled in any kernel because there is no functional
43	change with not instrumented initrds.
46	3) How does it work
47	-------------------
49	# Extract the machine's ACPI tables:
50	cd /tmp
51	acpidump >acpidump
52	acpixtract -a acpidump
53	# Disassemble, modify and recompile them:
54	iasl -d *.dat
55	# For example add this statement into a _PRT (PCI Routing Table) function
56	# of the DSDT:
57	Store("HELLO WORLD", debug)
58	# And increase the OEM Revision. For example, before modification:
59	DefinitionBlock ("DSDT.aml", "DSDT", 2, "INTEL ", "TEMPLATE", 0x00000000)
60	# After modification:
61	DefinitionBlock ("DSDT.aml", "DSDT", 2, "INTEL ", "TEMPLATE", 0x00000001)
62	iasl -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.
71	mkdir -p kernel/firmware/acpi
72	cp dsdt.aml kernel/firmware/acpi
73	# A maximum of "NR_ACPI_INITRD_TABLES (64)" tables are currently allowed
74	# (see osl.c):
75	iasl -sa facp.dsl
76	iasl -sa ssdt1.dsl
77	cp facp.aml kernel/firmware/acpi
78	cp 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:
83	find kernel | cpio -H newc --create > /boot/instrumented_initrd
84	cat /boot/initrd >>/boot/instrumented_initrd
85	# reboot with increased acpi debug level, e.g. boot params:
86	acpi.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"
91	iasl is able to disassemble and recompile quite a lot different,
92	also static ACPI tables.
95	4) Where to retrieve userspace tools
96	------------------------------------
98	iasl and acpixtract are part of Intel's ACPICA project:
99	http://acpica.org/
100	and should be packaged by distributions (for example in the acpica package
101	on SUSE).
103	acpidump can be found in Len Browns pmtools:
104	ftp://kernel.org/pub/linux/kernel/people/lenb/acpi/utils/pmtools/acpidump
105	This tool is also part of the acpica package on SUSE.
106	Alternatively, used ACPI tables can be retrieved via sysfs in latest kernels:
107	/sys/firmware/acpi/tables
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