74 lines
3.1 KiB
Plaintext
74 lines
3.1 KiB
Plaintext
|
Linux ACPI Custom Control Method How To
|
||
|
|
=======================================
|
||
|
|
|
||
|
|
Written by 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.
|
||
|
|
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).
|