Comment 0 for bug 993802

3D acceleration doesn't seem to work on the PAE kernel (which Ubuntu has made the default in my grub menu). The screen goes black (signal lost) after leaving grub, and only comes back with the login menu. If I use the non-PAE kernel, same version and everything, it seems to work. I've provided snippets of dmesg and xorg logs of both. Significant differences, I've noticed:

PAE Xorg.0.log:
[ 25.741] (II) RADEON(0): GPU accel disabled or not working, using shadowfb for KMS
[ 25.750] (II) RADEON(0): KMS Color Tiling: disabled

PAE: [ 25.741] (II) RADEON(0): GPU accel disabled or not working, using shadowfb for KMS
non-PAE: [ 22.066] (II) RADEON(0): mem size init: gart size :1fdff000 vram size: s:40000000 visible:3f7d7000
(an extra digit included?)

and PAE dmesg:
[ 2.046120] [drm] Loading RS690/RS740 Microcode
[ 2.057778] [drm] radeon: ring at 0x0000000060001000
[ 2.194499] [drm:r100_ring_test] *ERROR* radeon: ring test failed (scratch(0x15E4)=0xCAFEDEAD)
[ 2.194502] [drm:r100_cp_init] *ERROR* radeon: cp isn't working (-22).
[ 2.194506] radeon 0000:01:05.0: failed initializing CP (-22).
[ 2.194508] radeon 0000:01:05.0: Disabling GPU acceleration
[ 2.318118] [drm:r100_cp_fini] *ERROR* Wait for CP idle timeout, shutting down CP.
[ 2.440936] Failed to wait GUI idle while programming pipes. Bad things might happen.
[ 2.441053] [drm] radeon: cp finalized

$ lsb_release -rd

Description: Ubuntu 12.04 LTS
Release: 12.04

$ apt-cache policy linux-image-3.2.0-24-generic-pae:

linux-image-3.2.0-24-generic-pae:
  Installed: 3.2.0-24.38
  Candidate: 3.2.0-24.38
  Version table:
 *** 3.2.0-24.38 0
        500 http://archive.ubuntu.com/ubuntu/ precise-proposed/main i386 Packages
        100 /var/lib/dpkg/status
     3.2.0-24.37 0
        500 http://archive.ubuntu.com/ubuntu/ precise-updates/main i386 Packages