The PowerPC pull request for the Linux 3.17 merge window reveals that support for pre-POWER4 hardware is being eliminated. Among the affected hardware is POWER3 and IBM RS64 processors, which are from the late 90's. POWER3 was used in IBM RS/6000 servers at the time and clocked at only a few hundred megahertz. Support for the old POWER hardware is being dropped since its Linux usage is minimal these days and the support was already regressed for some kernel releases.
Benjamin Herrenschmidt wrote in the pull request, "The biggest bit is Michael [Ellerman] removing all of pre-POWER4 processor support from the 64-bit kernel. POWER3 and rs64. This gets rid of a ton of old cruft that has been bitrotting in a long while. It was broken for quite a few versions already and nobody noticed. Nobody uses those machines anymore. While at it, he cleaned up a bunch of old dusty cabinets, getting rid of a skeletton or two."
Added for newer PowerPC hardware with Linux 3.17 is basic VFIO support for KVM to allow assigning PCI devices to KVM guests and other features and changes also made it for this merge window.