Comment # 16 on bug 67276 from Alex Deucher

(In reply to comment #15)
> Do you have any idea, why this happens randomly on cold boots but not when
> restarting the pc? I think the whole initialization process should be the
> same everytime the system is booted, so that the ring initialization should
> fail every time.
> 
> On I side note: Earlier I had an interesting problem. When rebooting the pc
> after a drm-lockup I could see the last screen before the restart. This
> means that some memory buffers were not completely cleared during the
> reboots.

Memory is never explicitly cleared.

> 
> Maybe I have a similar problem here: The faulty register isn't rewritten on
> every reboot???

The only way to figure out what is going on is to bisect.  There are a lot of
things that could cause ring tests to fail.