Not to be confused with the modern Compute Express Link (CXL) standard, but IBM’s Coherent Accelerator Interface “CXL” / Coherent Accelerator Processor Interface “CAPI” support was stripped away today from the mainline Linux kernel.
IBM’s CXL pre-dates the modern Compute Express Link multi-vendor effort as an effort that began more than one decade ago. IBM in 2022 in fact donated the OpenCAPI specifications to the CXL Consortium. The Coherent Accelerator Processor Interface was an early effort for helping external GPUs / ASICs / accelerators atop PCI Express for directly connecting to CPUs.
Last year I wrote about IBM deprecating the CXL coherent accelerator and CAPI flash drivers. As part of obsoleting/deprecating them, they became disabled by default and a warning printed to users in the event the drivers were built and loaded. IBM engineers aren’t aware of anyone still using CAPI devices in production and especially those that would be running an upstream mainline Linux kernel build.
With no objections to deprecating IBM CXL, Linux 6.15 is going ahead and stripping away the Coherent Accelerator Processor Interface code. This merge today removes the IBM CAPI driver code for Linux 6.15. Removing this seemingly unused code today from the modern kernel lightens the source tree by 14.3k lines of code.
This follows the IBM POWER pull request for Linux 6.15 last week that separately removed support for aging IBM Cell Blade servers. Looks to be some spring cleaning over at IBM.
