I found out that libdrm may be relevant too:
http://packages.debian.org/changelogs/pool/main/libd/libdrm/libdrm_2.4.18-3/changelog#versionversion2.4.18-1
libdrm (2.4.17-1) unstable; urgency=low
[...]
* Enable libdrm_radeon, interface to kernel graphics memory management on
radeon (closes: #558786).
[...]
-- Brice Goglin <bgoglin@debian.org> Sun, 31 Jan 2010 20:12:38 +0100
I'll try to revert this package as well.