Zhang Rui | a1a541d | 2009-12-02 13:31:00 +0800 | [diff] [blame] | 1 | Linux ACPI Custom Control Method How To |
| 2 | ======================================= |
| 3 | |
| 4 | Written by Zhang Rui <rui.zhang@intel.com> |
| 5 | |
| 6 | |
| 7 | Linux supports customizing ACPI control methods at runtime. |
| 8 | |
| 9 | Users can use this to |
| 10 | 1. override an existing method which may not work correctly, |
| 11 | or just for debugging purposes. |
| 12 | 2. insert a completely new method in order to create a missing |
| 13 | method such as _OFF, _ON, _STA, _INI, etc. |
| 14 | For these cases, it is far simpler to dynamically install a single |
| 15 | control method rather than override the entire DSDT, because kernel |
| 16 | rebuild/reboot is not needed and test result can be got in minutes. |
| 17 | |
| 18 | Note: Only ACPI METHOD can be overridden, any other object types like |
| 19 | "Device", "OperationRegion", are not recognized. |
| 20 | Note: The same ACPI control method can be overridden for many times, |
| 21 | and it's always the latest one that used by Linux/kernel. |
Zhang Rui | c637e48 | 2010-07-15 10:46:17 +0800 | [diff] [blame] | 22 | Note: To get the ACPI debug object output (Store (AAAA, Debug)), |
| 23 | please run "echo 1 > /sys/module/acpi/parameters/aml_debug_output". |
Zhang Rui | a1a541d | 2009-12-02 13:31:00 +0800 | [diff] [blame] | 24 | |
| 25 | 1. override an existing method |
| 26 | a) get the ACPI table via ACPI sysfs I/F. e.g. to get the DSDT, |
| 27 | just run "cat /sys/firmware/acpi/tables/DSDT > /tmp/dsdt.dat" |
| 28 | b) disassemble the table by running "iasl -d dsdt.dat". |
| 29 | c) rewrite the ASL code of the method and save it in a new file, |
| 30 | d) package the new file (psr.asl) to an ACPI table format. |
| 31 | Here is an example of a customized \_SB._AC._PSR method, |
| 32 | |
| 33 | DefinitionBlock ("", "SSDT", 1, "", "", 0x20080715) |
| 34 | { |
| 35 | External (ACON) |
| 36 | |
| 37 | Method (\_SB_.AC._PSR, 0, NotSerialized) |
| 38 | { |
| 39 | Store ("In AC _PSR", Debug) |
| 40 | Return (ACON) |
| 41 | } |
| 42 | } |
| 43 | Note that the full pathname of the method in ACPI namespace |
| 44 | should be used. |
| 45 | And remember to use "External" to declare external objects. |
| 46 | e) assemble the file to generate the AML code of the method. |
| 47 | e.g. "iasl psr.asl" (psr.aml is generated as a result) |
| 48 | f) mount debugfs by "mount -t debugfs none /sys/kernel/debug" |
| 49 | g) override the old method via the debugfs by running |
| 50 | "cat /tmp/psr.aml > /sys/kernel/debug/acpi/custom_method" |
| 51 | |
| 52 | 2. insert a new method |
| 53 | This is easier than overriding an existing method. |
| 54 | We just need to create the ASL code of the method we want to |
| 55 | insert and then follow the step c) ~ g) in section 1. |
| 56 | |
| 57 | 3. undo your changes |
| 58 | The "undo" operation is not supported for a new inserted method |
| 59 | right now, i.e. we can not remove a method currently. |
Masahiro Yamada | 0367105 | 2017-02-27 14:29:28 -0800 | [diff] [blame] | 60 | For an overridden method, in order to undo your changes, please |
Zhang Rui | a1a541d | 2009-12-02 13:31:00 +0800 | [diff] [blame] | 61 | save a copy of the method original ASL code in step c) section 1, |
| 62 | and redo step c) ~ g) to override the method with the original one. |
| 63 | |
| 64 | |
| 65 | Note: We can use a kernel with multiple custom ACPI method running, |
| 66 | But each individual write to debugfs can implement a SINGLE |
| 67 | method override. i.e. if we want to insert/override multiple |
| 68 | ACPI methods, we need to redo step c) ~ g) for multiple times. |
Thomas Renninger | 526b4af | 2011-05-26 12:26:24 +0200 | [diff] [blame] | 69 | |
| 70 | Note: Be aware that root can mis-use this driver to modify arbitrary |
| 71 | memory and gain additional rights, if root's privileges got |
| 72 | restricted (for example if root is not allowed to load additional |
| 73 | modules after boot). |