firmware-guide/acpi/method-customizing.rst

1 .. SPDX-License-Identifier: GPL-2.0
4 Linux ACPI Custom Control Method How To
14 1. override an existing method which may not work correctly,
16 2. insert a completely new method in order to create a missing
17    method such as _OFF, _ON, _STA, _INI, etc.
20 control method rather than override the entire DSDT, because kernel
25   - Only ACPI METHOD can be overridden, any other object types like
29   - The same ACPI control method can be overridden for many times,
32   - To get the ACPI debug object output (Store (AAAA, Debug)),
38 1. override an existing method
42 b) disassemble the table by running "iasl -d dsdt.dat".
43 c) rewrite the ASL code of the method and save it in a new file,
45    Here is an example of a customized \_SB._AC._PSR method::
49          Method (\_SB_.AC._PSR, 0, NotSerialized)
56    Note that the full pathname of the method in ACPI namespace
58 e) assemble the file to generate the AML code of the method.
59    e.g. "iasl -vw 6084 psr.asl" (psr.aml is generated as a result)
60    If parameter "-vw 6084" is not supported by your iASL compiler,
62 f) mount debugfs by "mount -t debugfs none /sys/kernel/debug"
63 g) override the old method via the debugfs by running
66 2. insert a new method
68 This is easier than overriding an existing method.
69 We just need to create the ASL code of the method we want to
74 The "undo" operation is not supported for a new inserted method
75 right now, i.e. we can not remove a method currently.
76 For an overridden method, in order to undo your changes, please
77 save a copy of the method original ASL code in step c) section 1,
78 and redo step c) ~ g) to override the method with the original one.
81 .. note:: We can use a kernel with multiple custom ACPI method running,
83    method override. i.e. if we want to insert/override multiple
86 .. note:: Be aware that root can mis-use this driver to modify arbitrary
89    modules after boot).