Four Decades After Introduction, Linux's VMEbus Support To Return To Demoted State

Introduced in the early 80's for the Motorola 68000 series was Versa Module Eurocard "VMEbus" standard that continues to see industrial uses. While still seeing some reported use today, unfortunately the same cannot be said for the quality of the VMEbus Linux support. After the VME subsystem was promoted out of staging a decade ago, the VME hardware drivers failed to ever leave staging and the code has fallen into disrepair and no maintenance now for the past half-decade. So the VME subsystem support is preparing to depart back to the land of the kernel's staging area.

With a patch to remove the CA91CX42 Universe-II driver, Arnd Bergmann is preparing to move the entire VME subsystem back to the staging area. As for the driver being removed outright, Bergmann noted, "This is one of four remaining drivers using the ancient virt_to_bus() interface instead of the dma-mapping interface, making it incompatible with most modern machines. As nobody has cleaned this up, there is a high chance that this driver has no actual users. The chip was introduced in 1997 and only supports 32-bit legacy PCI. It was replaced by TSI148 in 2004, but that chip has since been discontinued, while a version of the older Universe II remains in production after 25 years. The vme_vmivme7805 board uses Universe-II, so this also gets removed in the process, but PCI add-on cards based on TSI148 can still work in theory."

As for moving the entire VME subsystem back to staging, the patch sums it up that maintenance of the drivers and subsystem itself effectively stopped in 2017, no hardware drivers remain in staging, and there is just the limited user-level access code that remains around.

A VMEbus presentation as part of this cern.ch school program.

Those interested in (re)learning more about the VME bus can see this CERN presentation.

Meanwhile the VME Linux web page hasn't been updated since 2003.

These patches demoting the VME code is currently in "staging-testing" and in turn should end up landing later this summer for Linux 5.20 into the mainline kernel. From there we'll see if anyone shows any signs of interest in the VMEbus support for the modern Linux kernel or if ultimately it will be removed in time.