A patch referencing this bug report has been merged in Linux v3.7-rc5:

commit 860fe2f05fa2eacac84368e23547ec8cf3cc6652
Author: Alex Deucher <alexander.deucher@amd.com>
Date:   Thu Nov 8 10:08:04 2012 -0500

    drm/radeon/cayman: add some missing regs to the VM reg checker