Clearing Out Linux's Old 32-bit ARM Platform Code Is Itself A Challenge

Longtime ARM Linux maintainer Arnd Bergmann over the past year has been working to clear out a number of old ARM platforms from the mainline kernel tree. With Linux 7.3 many older 32-bit ARM platforms were deprecated and in turn hundreds of kernel drivers orphaned. Now it's on to removing that actual code, which given the amount of entangled code, is itself a challenge. Among the code planning to be removed following the recent deprecation is for the SA1100, Footbridge, RISCPC, Orion / Dove / MV78xx0, OMAP24xx, i.MX31, i.MX targets without an MMU, LPC18xx, STM32f4/f7/h7 MCUs, Versatile MPS2, AT91 SAMV7, Axxia, and legacy PXA board files. Of that platform code specifically it's around 55k lines of code. But getting to the then-unused kernel drivers and the like becomes around ~247k lines of kernel code on the chopping block. Arnd Bergmann provided a status update on the undertaking this week. He noted that clearing out the deprecated platform code ended up being a larger effort than expected and is now up to around 300 patches. He wrote on the LKML: "In the 7.3 kernel, I marked a number of platforms and features as deprecated, with the plan to keep these around for the LTS kernel, but remove them in 7.4. Cleaning out the deprecated platform code has turned into a larger effort than I expected, currently standing at 300 patches, with a lot of them still in need of being split up into smaller ones. The first series here removes just the bits in arch/arm/mach-*/, plus the portions that directly depend on the removed Kconfig symbols where these are trivial to remove. The parts that are not included are those that remove architectural features and device drivers that become unused after this series. The RiscPC platform that was marked as deprecated is left in place for the moment, as there was still some discussion about reviving compiler support for it." Depending upon how the Linux 7.3 release schedule plays out, it's still possible that Linux 7.4 will be released in 2026 and could be declared this year's Long Term Support (LTS) version. In which case the actual removal likely wouldn't be until Linux 7.5, but we'll see how the LTS situation plays out with Greg Kroah-Hartman. In any case the effort is still ongoing for clearing out a lot of old, likely unused Arm platform code that is only getting the attraction these days of AI/LLM agents.