CXL Bring-Up continues – No more infrastructure for Linux 5.14, “No more meat” for Linux 5.15


Intel’s open source engineers continue to work on implementing Compute Express Link (CXL) as a new open standard interconnect built on PCIe aimed at strengthening next-generation servers.

Earlier this year with Linux 5.12, initial support for Compute Express Link 2.0 was released with an initial focus on enabling support for VXL 2.0 Type-3 memory devices. This CXL core infrastructure work has continued ever since and is still led by Intel engineers.

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

Dan Williams of Intel summarized the current events of CXL Linux via the Linux Kernel mailing list:

This subsystem is still under construction, as the bulk of the update consists of enumeration improvements and device model expansion. In terms of new features, more mailbox commands have been added to the allowed list to support persistent memory provisioning support targeting v5.15. The enumeration-critical update is support for the CXL fixed memory window structure which tells Linux the decoded system physical address ranges for CXL host bridges in the system. This allows the driver to detect which address ranges have been mapped by the firmware and which address ranges are available for future hot plugging.

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 would also be supported by AMD EPYC 7004 “Genoa” processors.

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