How to get debug information?

[Floris]

I'm testing the new Nvidia driver module with drm enabled. It is very  
experimental so I know there are bugs in it. I think I found a problem and  
I want to get more information about it from the log messages, but the  
whole system freezes. I can't ssh into the system or change to a tty.  
After a hard reboot the last lines in journalctl are:
        kernel: usb 2-1.7: current rate 0 is different from the runtime rate 
48000
        Failed to get journal fields
Not very useful
Is there a way to get more information?
Floris