Debugging hang on resume from STR?

[Jani Monoses]

Hello,

I am having a regression on Ubuntu 10.10 vs 10.04.
In a dual monitor setup on a laptop with the card

01:00.0 VGA compatible controller: ATI Technologies Inc M24 1P [Radeon 
Mobility X600]
( 01:00.0 0300: 1002:3150 )

on resuming from suspend to RAM the machine locks up, no pings, no 
caps-lock toggling, blank screen.

It works fine if I quit X by killing GDM and run pm-suspend in VT mode.
It also works fine in X if I unplug the external monitor and use a 
single screen only.
And finally and luckily it works in X with both monitors if I set radeon 
modeset=0 in radeon-kms.conf

Still I'd like to help debug this issue so it works without changes to 
the system, any pointers?

Jani