acpi suspend debugging techniques?

I would appreciate any pointers at how to debug an ACPI suspend problem that I have.

What I have so far.  The system hangs when I try to suspend it and it gets reset
by a watchdog.  Setting debug.acpi.suspend_bounce=1 does not make any
difference, so the hang happens before the final sleep code is executed.  I
think that the device suspend stage is executed, because disks get spun down and
video signals gets cut off.

I could enable / add some debug printfs, but I suppose that their output would
get lost due to the above.  RAM content unfortunately does not survive across
the resets.

-- 
Andriy Gapon