After installing the fglrx driver everything is ok, but when I install blackbox (yeah I like blackbox it's simple) and I make a custom xsession and log into it, the resolution is ok but the displayed size of the desktop is smaller then the screen and the mouse cursor is just displayed as an X.
.xinitrc there are only 2 things, a chromium-browser autostart script and
exec blackbox, no extra configuration.
I don't see any relevant thing in the logs, no errors. The videocard is a Radeon HD 6430M. Thank you in advance!