Comment # 6 on bug 45291 from p3we

This issue also occurs on Dell U2312MH monitor connected to ATI Mobility Radeon
540v (RV710) over DisplayPort. The driver properly detects plugged monitor and
discover all capabilities but there is no signal on DisplayPort. After short
time monitor goes to sleep mode.

I have tried all available modes with no success. VGA output works fine.

I have tested this configuration under Windows and DisplayPort works as
expected, so it is no a hardware problem.