CXL Bring-Up Continues - More Infrastructure For Linux 5.14, "More Meat" For Linux 5.15

Intel open-source engineers continue working on the bring-up around Compute Express Link (CXL) as the new open standard interconnect built off PCIe aiming to empower next-generation servers.

Earlier this year with Linux 5.12 the initial Compute Express Link 2.0 support was published with an initial focus on enabling VXL 2.0 Type-3 Memory Device support. That CXL kernel infrastructure work has continued since and still led by Intel engineers.

With Linux 5.14 is another batch of infrastructure work around Compute Express Link that is mostly about the fundamentals and not too exciting for end-users. However, with Linux 5.15 there should be "more meat" around the CXL device support landing.

Intel's Dan Williams summed up the current CXL Linux happenings via the Linux kernel mailing list:

This subsystem is still in the build-out phase as the bulk of the update is improvements to enumeration and fleshing out the device model. In terms of new features, more mailbox commands have been added to the allowed-list in support of persistent memory provisioning support targeting v5.15. The critical update from an enumeration perspective is support for the CXL Fixed Memory Window Structure that indicates to Linux which system physical address ranges decode to the CXL Host Bridges in the system. This allows the driver to detect which address ranges have been mapped by firmware and what address ranges are available for future hotplug.

So, again, mostly skeleton this round, with more meat targeting v5.15.

Compute Express Link support will be found with Intel's Xeon Scalable "Sapphire Rapids" processors and also rumored to be supported by AMD EPYC 7004 "Genoa" processors as well.