I have the same board AMD a6-3400m with a Radeon ATI hd 6520. (Its on a HP notebook I got at a very good price...).
I'm still trying to make it work with the open source driver without success (x11-drivers/xf86-video-ati).
I'm on Funtoo (based on gentoo) with the 3.1.0-rc4-git2 kernel, and masked versions of Xorg and video drivers, libdrm, libkms, mesa, ...).
I had the same problem but I was able to connect to the machine with ssh from my other machine. You have to install & config sshd before in a chrooted shell on your machine.
I have enable the following kernel options for frame buffer :
CONFIG_FB=y
CONFIG_FB_CFB_FILLRECT=m
CONFIG_FB_CFB_COPYAREA=m
CONFIG_FB_CFB_IMAGEBLIT=m
CONFIG_FB_MODE_HELPERS=y
and for radeon:
CONFIG_DRM_RADEON=m
CONFIG_DRM_RADEON_KMS=y
# CONFIG_FB_RADEON is not set
But I think You should set "CONFIG_DRM_RADEON_KMS=n" instead.
Take a look at
http://xorg.freedesktop.org/wiki/radeonBuildHowTo
in case of trouble (black screen), if you use grub to start, try to edit the grub command and add "vga=711" kernel options or (radeon.modeset=0). I can't confirm now. But I think the AMD ATI Radeon HD 6520 is only usable with the proprietary drivers from ATI. This card is too recent right now (mid april 2011). May be in a few months it will be ready.
Regards,
Bernard
