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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/firmware-guide/acpi/method-customizing.rst | |
parent | Initial commit. (diff) | |
download | linux-430c2fc249ea5c0536abd21c23382884005c9093.tar.xz linux-430c2fc249ea5c0536abd21c23382884005c9093.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/firmware-guide/acpi/method-customizing.rst')
-rw-r--r-- | Documentation/firmware-guide/acpi/method-customizing.rst | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/Documentation/firmware-guide/acpi/method-customizing.rst b/Documentation/firmware-guide/acpi/method-customizing.rst new file mode 100644 index 000000000..de3ebcaed --- /dev/null +++ b/Documentation/firmware-guide/acpi/method-customizing.rst @@ -0,0 +1,89 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================================= +Linux ACPI Custom Control Method How To +======================================= + +:Author: Zhang Rui <rui.zhang@intel.com> + + +Linux supports customizing ACPI control methods at runtime. + +Users can use this to: + +1. override an existing method which may not work correctly, + or just for debugging purposes. +2. insert a completely new method in order to create a missing + method such as _OFF, _ON, _STA, _INI, etc. + +For these cases, it is far simpler to dynamically install a single +control method rather than override the entire DSDT, because kernel +rebuild/reboot is not needed and test result can be got in minutes. + +.. note:: + + - Only ACPI METHOD can be overridden, any other object types like + "Device", "OperationRegion", are not recognized. Methods + declared inside scope operators are also not supported. + + - The same ACPI control method can be overridden for many times, + and it's always the latest one that used by Linux/kernel. + + - To get the ACPI debug object output (Store (AAAA, Debug)), + please run:: + + echo 1 > /sys/module/acpi/parameters/aml_debug_output + + +1. override an existing method +============================== +a) get the ACPI table via ACPI sysfs I/F. e.g. to get the DSDT, + just run "cat /sys/firmware/acpi/tables/DSDT > /tmp/dsdt.dat" +b) disassemble the table by running "iasl -d dsdt.dat". +c) rewrite the ASL code of the method and save it in a new file, +d) package the new file (psr.asl) to an ACPI table format. + Here is an example of a customized \_SB._AC._PSR method:: + + DefinitionBlock ("", "SSDT", 1, "", "", 0x20080715) + { + Method (\_SB_.AC._PSR, 0, NotSerialized) + { + Store ("In AC _PSR", Debug) + Return (ACON) + } + } + + Note that the full pathname of the method in ACPI namespace + should be used. +e) assemble the file to generate the AML code of the method. + e.g. "iasl -vw 6084 psr.asl" (psr.aml is generated as a result) + If parameter "-vw 6084" is not supported by your iASL compiler, + please try a newer version. +f) mount debugfs by "mount -t debugfs none /sys/kernel/debug" +g) override the old method via the debugfs by running + "cat /tmp/psr.aml > /sys/kernel/debug/acpi/custom_method" + +2. insert a new method +====================== +This is easier than overriding an existing method. +We just need to create the ASL code of the method we want to +insert and then follow the step c) ~ g) in section 1. + +3. undo your changes +==================== +The "undo" operation is not supported for a new inserted method +right now, i.e. we can not remove a method currently. +For an overridden method, in order to undo your changes, please +save a copy of the method original ASL code in step c) section 1, +and redo step c) ~ g) to override the method with the original one. + + +.. note:: We can use a kernel with multiple custom ACPI method running, + But each individual write to debugfs can implement a SINGLE + method override. i.e. if we want to insert/override multiple + ACPI methods, we need to redo step c) ~ g) for multiple times. + +.. note:: Be aware that root can mis-use this driver to modify arbitrary + memory and gain additional rights, if root's privileges got + restricted (for example if root is not allowed to load additional + modules after boot). |