Comment 42 for bug 703553

If I'm correct, this is the patch that broke it:

commit 6f15f605120331a44aeacb4fca5550e2dfb92204
Author: Alex Deucher <email address hidden>
Date: Mon Oct 25 19:44:00 2010 -0400

    drm/radeon/kms: MC vram map needs to be >= pci aperture size

    BugLink: http://bugs.launchpad.net/bugs/690730

    commit b7d8cce5b558e0c0aa6898c9865356481598b46d upstream.

    The vram map in the radeon memory controller needs to be
    >= the pci aperture size. Fixes:
    https://bugs.freedesktop.org/show_bug.cgi?id=28402

    The problematic cards in the above bug have 64 MB of vram,
    but the pci aperture is 128 MB and the MC vram map was only
    64 MB. This can lead to hangs.

    Signed-off-by: Alex Deucher <email address hidden>
    Signed-off-by: Dave Airlie <email address hidden>
    Signed-off-by: Greg Kroah-Hartman <email address hidden>
    Signed-off-by: Andi Kleen <email address hidden>
    Signed-off-by: Brad Figg <email address hidden>

diff --git a/drivers/gpu/drm/radeon/r100.c b/drivers/gpu/drm/radeon/r100.c
index a89a15a..5c37c48 100644
--- a/drivers/gpu/drm/radeon/r100.c
+++ b/drivers/gpu/drm/radeon/r100.c
@@ -2321,6 +2321,9 @@ void r100_vram_init_sizes(struct radeon_device *rdev)
                /* Fix for RN50, M6, M7 with 8/16/32(??) MBs of VRAM -
                 * Novell bug 204882 + along with lots of ubuntu ones
                 */
+ if (rdev->mc.aper_size > config_aper_size)
+ config_aper_size = rdev->mc.aper_size;
+
                if (config_aper_size > rdev->mc.real_vram_size)
                        rdev->mc.mc_vram_size = config_aper_size;
                else