You're using the Xorg modesetting driver, not the xf86-video-ati radeon driver. Does the problem also occur with the latter? If yes, please attach the corresponding Xorg log file and output of dmesg.
You're using the Xorg modesetting driver, not the xf86-video-ati radeon driver. Does the problem also occur with the latter? If yes, please attach the corresponding Xorg log file and output of dmesg.