Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
Operation regions are regions in some space that contain hardware registers for exclusive use by
ACPI control methods. In general, no hardware register (at least byte-granular) within the operation
region accessed by an ACPI control method can be shared with any accesses from any other source,
with the exception of using the Global Lock to share a region with the firmware. The entire
Operation Region can be allocated for exclusive use to the ACPI subsystem in the host OS.
Operation Regions that are defined within the scope of a method are the exception to this rule. These
Operation Regions are known as “Dynamic” since the OS has no idea that they exist or what
registers they use until the control method is executed. Using a Dynamic SystemIO or
SystemMemory Operation Region is not recommended since the OS cannot guarantee exclusive
access. All other types of Operation Regions may be Dynamic.
Operation Regions define the overall base address and length of a hardware region, but they cannot
be accessed directly by AML code. A Field object containing one or more FieldUnits is used to
overlay the Operation Region in order to access individual areas of the Region. An individual
FieldUnit within an Operation Region may be as small as one bit, or as large as the length of the
entire Region. FieldUnit values are normalized (shifted and masked to the proper length.) The data
type of a FieldUnit can be either a Buffer or an Integer, depending on the bit length of the
FieldUnit. If the FieldUnit is smaller than or equal to the size of an Integer (in bits), it will be treated
as an Integer. If the FieldUnit is larger than the size of an Integer, it will be treated as a Buffer. The
size of an Integer is indicated by the DSDT header’s Revision field. A revision less than 2 indicates
that the size of an Integer is 32 bits. A value greater than or equal to 2 signifies that the size of an
Integer is 64 bits. For more information about data types and FieldUnit type conversion rules, see
Section 19.3.5.7, “Data Type Conversion Rules”.
An Operation Region object implicitly supports Mutex synchronization. Updates to the object, or a
Field data object for the region, will automatically synchronize on the Operation Region object;
however, a control method may also explicitly synchronize to a region to prevent other accesses to
the region (from other control methods). Notice that according to the control method execution
model, control method execution is non-preemptive. Because of this, explicit synchronization to an
Operation Region needs to be done only in cases where a control method blocks or yields execution
and where the type of register usage requires such synchronization.
The predefined Operation Region types specified in ACPI are shown in the table below:
Table 19-371 Predefined Operation Region types
Name (RegionSpace Keyword)
Value
SystemMemory 0
SystemIO 1
PCI_Config 2
EmbeddedControl 3
SMBus 4
SystemCMOS 5
PCIBARTarget 6
IPMI 7
GeneralPurposeIO 8
GenericSerialbus 9
870 April, 2015 Version 6.0