instant reboot with new drm

Ever since the new DRM was imported I have been unable to use DRI with 
my R128-based card.  When loading X, the machine reboots.  Removing DRI 
from the X config makes everything work.  The last message logged by X 
when DRI is enabled:
(II) R128(0): [drm] installed DRM signal handler
(II) R128(0): [DRI] installation complete
(II) R128(0): [drm] Added 128 16384 byte vertex/indirect buffers
(II) R128(0): [drm] Mapped 128 vertex/indirect buffers
(II) R128(0): [drm] dma control initialized, using IRQ 5
(II) R128(0): Direct rendering enabled
(==) RandR enabled
(**) Option "BaudRate" "1200"
(**) Option "StopBits" "2"
(**) Option "DataBits" "8"
(**) Option "Parity" "None"
(**) Option "Vmin" "1"
(**) Option "Vtime" "0"
(**) Option "FlowControl" "None"

The card is detected as follows:
drm0: <ATI Rage 128 Mobility LF (AGP)> port 0x9000-0x90ff mem 
0xf8000000-0xfbffffff,0xf0200000-0xf0203fff irq 5 at device 0.0 on pci1
info: [drm] AGP at 0xf4000000 64MB
info: [drm] Initialized r128 2.5.0 20030725 on minor 0

Note that IRQ5 is shared with the sound card (snd_solo(4)) and that I am 
using APIC and ACPI.  Here's the pciconf:
drm0_at_pci1:0:0:  class=0x030000 card=0xb11b0e11 chip=0x4c461002 rev=0x02 
hdr=0x00    vendor   = 'ATI Technologies Inc'
     device   = 'Rage Mobility M3 AGP 2x'
     class    = display
     subclass = VGA

DRM is compiled into kernel, although I originally was using modules:
# Direct Rendering modules for 3D acceleration.
device          drm             # DRM core module required by DRM drivers
device          r128drm         # ATI Rage 128

How can I debug this?
Jon