Comment 38 for bug 1412730

Christopher,

Vivid with fglrx: none off the reported issues exist. U2415 is detected every time, display resolution is right, also dpms powersaving works as expected. In ATI control Center all hardware is detected. Also no xrandr issues
Trusty with fglrx: same as with vivid, none of the issues.

The main reason I'm not using fglrx is because it's proprietary, but also because the opensource radeon gives much better perfomance.
With fglrx there is lag in windows moving and resizing, also in videos. Next to that there is a lot of tearing visible. Whem turning on tear-free in Catalyst Control Center the lag gets even worse.

So fglrx is a workaround, but not a pleasant one. The lag and tearing is visible too many times during daily work.
At the moment I prefer my own workaround as mentioned above with the radeon driver and drm helper kernel parameter.
This way the displays work great without lag, but when booting, switching users in Unity or just going in suspend/standby I have to put the screen off and on a couple of times to get it out of standby.

One thing I noticed with the radeon driver: switching back and forth between vt7 and and another vt gets the U2415 out of standby too (eventually).