15:12

0h

RO

Reserved

11

0x0

RW

Link Autonomous Bandwidth Interrupt Enable (LABIE)

Link Autonomous Bandwidth Interrupt Enable - When Set, this bit enables the generation of an interrupt to indicate that the Link Autonomous Bandwidth Status bit has been Set.

10

0x0

RW

Link Bandwidth Management Interrupt Enable (LBMIE)

When Set, this bit enables the generation of an interrupt to indicate that the Link Bandwidth Management Status bit has been Set.
This bit is not applicable and is reserved for Endpoints, PCI Express-to-PCI/PCI-X bridges, and Upstream Ports of Switches.
Functions that do not implement the Link Bandwidth Notification Capability must hardwire this bit to 0b.
Default value of this bit is 0b.

9

0x0

RW

Hardware Autonomous Width Disable (HAWD)

When Set, this bit disables hardware from changing the Link width for reasons other than attempting to correct unreliable Link operation by reducing Link width.
Note: When operating as PCI Express, this bit defines the value of the Link Upconfigure Capability in TS2 Ordered Sets.
Default value of this bit is 0b.

8

0x0

RO

Enable Clock Power Management (ECPM)

Not supported on Root Ports.

7

0x0

RW

Extended Synch (ES)

Extended Sync

6

0x0

RW

Common Clock Configuration (CCC)

When set, indicates that the Root Port and device are operating with a distributed common reference clock.

5

0x0

WO

Retrain Link (RL)

When set, the root port will train its downstream link. This bit always returns 0 when read. Software uses LSTS.LT and LSTS.LTE to check the status of training.
It is permitted to write 1b to this bit while simultaneously writing modified values to other fields in this register. If the LTSSM is not already in Recovery or Configuration, the resulting Link training must use the modified values. If the LTSSM is already in Recovery or Configuration, the modified values are not required to affect the Link training that's already in progress.

4

0x0

RW

Link Disable (LD)

When set, the root port will disable the link by directing the LTSSM to the Disabled state.

3

0x0

RW/O

Read Completion Boundary Control (RCBC)

Indicates the read completion boundary is 64 bytes.

2

0h

RO

Reserved

1:0

0x0

RW

Active State Link PM Control (ASPM)

Indicates whether the root port should enter L0s or L1 or both.
Bits Definition
0: Disabled
1: L0s Entry Enabled
2: L1 Entry Enabled
3: L0s and L1 Entry Enabled
The value of this register is used unless the Root Port ASPM Control Override Enable register is set, in which case the Root Port ASPM Control Override value is used.
Note: If STRPFUSECFG.ASPMDIS is 1, hardware will always see 00 as an output from this register. BIOS reading this register should always return the correct value.