AMD's Alex Deucher sent out a patch on Friday to disable Dynamic Power Management on the RV770 by default. The DPM for the RV770 was enabled by default with the Linux 3.13 kernel and it yields better/lower power consumption while idling, better performance if the video BIOS sets lower clock speeds at boot time, and with the lower power consumption can also come lower heat output. However, some users have reported issues with RV770 GPUs in using the Linux 3.13 kernel and newer. (In my personal testing of several different RV770 GPUs, I haven't encountered any issues with Linux 3.13+.)
Among the issues reported is the Linux 3.13 kernel and newer hanging the machine now that Radeon DPM is enabled, a fatal machine check when booting Linux 3.13 with an RV770 GPU, and other kernel hanging problems. With this simple patch, RV770 DPM is now disabled by default with the simple message of "There seem to be stability issues on a number of cards."
AMD's Christian König has added this patch already to his merge queue for the Linux 3.15 kernel. Hopefully AMD developers will soon be able to sort out the RV770 GPU DPM issues given that this hardware was once very popular with AMD Linux users and is still found out in many systems with the GPUs having launched just six years ago.