Power-Saving PCI Express L1 PM Substate Support Coming To Linux 4.11

While hearing "ASPM" may still scare some of you from the Linux kernel power management woes of a few years ago, ASPM PCI-E L1 PM substate support is coming to Linux 4.11 to hopefully help with power savings for idle PCI Express devices.

For those unfamiliar with PCI Express L1 PM substate support, it's explained in full via this PCI SIG documentation. From there, "This ECR defines an optional mechanism, that establishes, depending on implementation, one or more substates of the L1 Link state, which allow for dramatically lower idle power, including near complete removal of power for high speed circuits...Current PCIe specifications do not provide mechanisms to enable very lower power consumption when a PCIe Link is idle. This limits the application of PCIe technologies in low-power and battery-based applications such as embedded, handheld and tablet computers. It also leads to excessive power waste in high-lane-count PCIe solutions such as desktops, servers, storage, and PCIe Switch-based solutions."

This L1 substate support can be enabled on supported hardware by building the kernel with the PCIEASPM_POWER_SUPERSAVE option. This work was done by Rajat Jain of Google.

This support is landing via the PCI pull request that also has a variety of other improvements too for Linux's PCI subsystem.