what about boot time? Do you have a full screen then? And what if you switch to a console when xorg is still running? Also, did you try this: https://wiki.archlinux.org/index.php/Kernel_Mode_Setting#Forcing_modes_and_EDID
Thanks for your help. - I have full screen at boot time ; - When I switch to an other tty, it is fullscreen ; - I'm trying the link.