radeon r100 GPU lockup *ERROR* radeon: ring test failed (scratch(0x15E8)=0xCAFEDEAD)

[rxrbln]

Apple G4 Cube ppc32:
kernel: radeon 0000:00:10.0: enabling device (0086 -> 0087)
kernel: [drm] initializing kernel modesetting (RV200 0x1002:0x5157 0x1002:0x5157 0x00).
kernel: [drm] Forcing AGP to PCI mode
kernel: radeon 0000:00:10.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xaa00
kernel: [drm] Not an x86 BIOS ROM, not using.
kernel: [drm] Using device-tree clock info
kernel: radeon 0000:00:10.0: VRAM: 128M 0x0000000098000000 - 0x000000009FFFFFFF (32M used)
kernel: radeon 0000:00:10.0: GTT: 512M 0x0000000078000000 - 0x0000000097FFFFFF
kernel: [drm] Detected VRAM RAM=128M, BAR=128M
kernel: [drm] RAM width 128bits DDR
kernel: [drm] radeon: 32M of VRAM memory ready
kernel: [drm] radeon: 512M of GTT memory ready.
kernel: [drm] GART: num cpu pages 131072, num gpu pages 131072
kernel: [drm] PCI GART of 512M enabled (table at 0x0000000004100000).
kernel: radeon 0000:00:10.0: WB disabled
kernel: radeon 0000:00:10.0: fence driver on ring 0 uses gpu addr 0x0000000078000000
kernel: [drm] radeon: irq initialized.
kernel: [drm] Loading R100 Microcode
kernel: [drm] radeon: ring at 0x0000000078001000
kernel: [drm] ring test succeeded in 0 usecs
kernel: [drm] ib test succeeded in 0 usecs
...
kernel: radeon 0000:00:10.0: ring 0 stalled for more than 10134msec
kernel: radeon 0000:00:10.0: GPU lockup (current fence id 0x00000000000003aa last fence id 0x00000000000003ab on ring 0)
kernel: radeon 0000:00:10.0: Saved 27 dwords of commands on ring 0.
kernel: radeon 0000:00:10.0: GPU reset succeeded, trying to resume
kernel: [drm] PCI GART of 512M enabled (table at 0x0000000003700000).
kernel: radeon 0000:00:10.0: WB disabled
kernel: radeon 0000:00:10.0: fence driver on ring 0 uses gpu addr 0x0000000078000000
kernel: [drm] radeon: ring at 0x0000000078001000
kernel: [drm:r100_ring_test [radeon]] ERROR radeon: ring test failed (scratch(0x15E8)=0xCAFEDEAD)
kernel: [drm:r100_cp_init [radeon]] ERROR radeon: cp isn't working (-22).

HP C9000 hppa64:
kernel: [drm] radeon: irq initialized.
kernel: [drm] Loading R400 Microcode
kernel: [drm] radeon: ring at 0xFFFFFFFFA8001000
kernel: [drm:r100_ring_test [radeon]] ERROR radeon: ring test failed (scratch(0x15E4)=0xCAFEDEAD)
kernel: [drm:r100_cp_init [radeon]] ERROR radeon: cp isn't working (-22).
kernel: radeon 0000:80:00.0: failed initializing CP (-22).
kernel: radeon 0000:80:00.0: Disabling GPU acceleration
kernel: [drm:r100_cp_fini [radeon]] ERROR Wait for CP idle timeout, shutting down CP.