X won't start with radeon (AMD R9 270X)

[jurgenxiv at t-online.de]

Hi, 

I'm having a problem getting X11 to work with my graphics card. 
X crashes on a new freebsd installation at startup with radeon driver. vesa works fine, but performance is not tolerable.
Is this a known problem or am I using the wrong configuration?

Please find attached 
- the output of dmesg
- the output of pciconf -lvbce
- the output of devinfo -vr
- the output of pkg info
- the xorg.conf file 
- the Xorg.log
- /etc/make.conf

Best regards,
Jurgen
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