question about radeon

[Onat I.]

I have Radeon HD 6520G card. I can only use it with vesa.
I don't care about acceleration but vesa doesn't support 16:9 aspect.
Everything looks fat. It's annoying. So I added appropriate lines to
/usr/src/sys/dev/pci/drm/radeon_drv.c and compiled the kernel.
When I rebooted, kernel recognized radeondrm. But Xorg still selects
vesa. If I create an /etc/X11/xorg.conf file. Screen freezes on running
startx. What other files do I need to edit? Or is it about the xorg driver?