Mobile GPUs like Adrenos (built into the Qualcomm Snapdragon CPUs) and VideoCore (in Raspberry Pis, basically Broadcom CPUs) also are starting to be supported on modern open-source graphics stacks. It is a bit hard to install regular Linux distros on most mobile devices (not in a chroot, but rather natively), so it will not matter for a while, but what used to be a strictly proprietary ground is now worked on in open projects - that is, once they are ready, they will be supported for as long as they're humanly usable and someone bothers to keep them updated, not when their manufacturers slap “
EOL” on the package and call it a day. Ancient GPUs like Voodoo still work under modern distros (that's stretching the definition of “humanly usable”, but hey, it works).