Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
optimizations / control policy and the performance impact of the platform's energy efficiency-related
optimizations / control policy.
Writes to this register only have meaning when Autonomous Selection is enabled.
8.4.7.1.8 OSPM Control Policy
8.4.7.1.8.1 In-Band Thermal Control
A processor using performance controls may be listed in a thermal zone’s _PSL list. If it is and the
thermal zone engages passive cooling as a result of passing the _PSV threshold, OSPM will apply
the ∆P[%] to modify the value in the desired performance register. Any time that passive cooling is
engaged, OSPM must also set the maximum performance register equal to the desired performance
register, to enforce the platform does not exceed the desired performance opportunistically.
Note: In System-on-Chip-based platforms where the SoC is comprised of multiple device components in
addition to the processor, OSPM’s use of the Desired and Maximum registers for thermal control
may not produce an optimal result because of SoC device interaction. The use of proprietary
package level thermal controls (if they exist) may produce more optimal results.
8.4.7.1.9 Using PCC Registers
If the PCC register space is used, all PCC registers must be defined to be in the same subspace.
OSPM will write registers by filling in the register value and issuing a PCC write command (see
Table 8-252). It may read static registers, counters, and the performance limited register by issuing a
read command (see Table 8-252). To amortize the cost of PCC transactions, OSPM should read or
write all PCC registers via a single read or write command when possible.
Table 8-252 PCC Commands Codes used by Collaborative Processor Performance Control
Command Description
0x00
0x01
0x02-0xFF
Read registers. Executed to request the platform update all registers for all enabled
processors with their current value.
Write registers. Executed to notify the platform one or more read/write registers for an
enabled processor has been updated.
All other values are reserved.
8.4.7.1.10 Relationship to other ACPI-defined Objects and Notifications
If _CPC is present, its use supersedes the use of the following existing ACPI objects:
• The P_BLK P_CNT register
• _PTC
• _TSS
• _TPC
• _TSD
• _TDL
• _PCT
• _PSS
490 April, 2015 Version 6.0