From 849369d6c66d3054688672f97d31fceb8e8230fb Mon Sep 17 00:00:00 2001 From: root Date: Fri, 25 Dec 2015 04:40:36 +0000 Subject: initial_commit --- Documentation/acpi/method-customizing.txt | 73 +++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 Documentation/acpi/method-customizing.txt (limited to 'Documentation/acpi/method-customizing.txt') diff --git a/Documentation/acpi/method-customizing.txt b/Documentation/acpi/method-customizing.txt new file mode 100644 index 00000000..5f55373d --- /dev/null +++ b/Documentation/acpi/method-customizing.txt @@ -0,0 +1,73 @@ +Linux ACPI Custom Control Method How To +======================================= + +Written by Zhang Rui + + +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. +Note: The same ACPI control method can be overridden for many times, + and it's always the latest one that used by Linux/kernel. +Note: 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) + { + External (ACON) + + 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. + And remember to use "External" to declare external objects. + e) assemble the file to generate the AML code of the method. + e.g. "iasl psr.asl" (psr.aml is generated as a result) + 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 overrided 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). -- cgit v1.2.3