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ACPICA commit 47f5607c204719d9239a12b889df725225098c8f
Module-level code refers to executable ASL code that runs during
table load. This is typically used in ASL to declare named objects
based on a condition evaluated during table load like so:
definition_block(...)
{
opreation_region (OPR1, system_memory, ...)
Field (OPR1)
{
FLD1, 8 /* Assume that FLD1's value is 0x1 */
}
/* The if statement below is referred to as module-level code */
If (FLD1)
{
/* Declare DEV1 conditionally */
Device (DEV1) {...}
}
Device (DEV2)
{
...
}
}
In legacy module-level code, the execution of the If statement
was deferred after other modules were loaded. The order of
code execution for the table above is the following:
1.) Load OPR1 to the ACPI Namespace
2.) Load FLD1 to the ACPI Namespace (not intended for drivers)
3.) Load DEV2 to the ACPI Namespace
4.) Execute If (FLD1) and load DEV1 if the condition is true
This legacy approach can be problematic for tables that look like the
following:
definition_block(...)
{
opreation_region (OPR1, system_memory, ...)
Field (OPR1)
{
FLD1, 8 /* Assume that FLD1's value is 0x1 */
}
/* The if statement below is referred to as module-level code */
If (FLD1)
{
/* Declare DEV1 conditionally */
Device (DEV1) {...}
}
Scope (DEV1)
{
/* Add objects DEV1's scope */
Name (OBJ1, 0x1234)
}
}
When loading this in the legacy approach, Scope DEV1 gets evaluated
before the If statement. The following is the order of execution:
1.) Load OPR1 to the ACPI Namespace
2.) Load FLD1 to the ACPI Namespace (not intended for drivers)
3.) Add OBJ1 under DEV1's scope -- ERROR. DEV1 does not exist
4.) Execute If (FLD1) and load DEV1 if the condition is true
The legacy approach can never succeed for tables like this due to the
deferral of the module-level code. Due to this limitation, a new
module-level code was developed. This new approach exeutes if
statements in the order that they appear in the definition block.
With this approach, the order of execution for the above defintion
block is as follows:
1.) Load OPR1 to the ACPI Namespace
2.) Load FLD1 to the ACPI Namespace (not intended for drivers)
3.) Execute If (FLD1) and load DEV1 because the condition is true
4.) Add OBJ1 under DEV1's scope.
Since DEV1 is loaded in the namespace in step 3, step 4 executes
successfully.
This change removes support for the legacy module-level code
execution. From this point onward, the new module-level code
execution will be the official approach.
Link: https://github.com/acpica/acpica/commit/47f5607c
Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.