Comment # 3 on bug 106229 from Luke-Jr

It did work with the "radeon" driver on x86, and *mostly* works with "radeon"
on POWER9 as well (except that it limits itself to 32-bit DMA for some reason,
and eventually crashes when I bump up against the allocation limit; to
workaround that, I am currently using the fbdev Xorg driver with the radeon
kernel driver).