Eric Anholt on Tuesday published the latest patches for runtime PM and GPU reset. While this is new functionality, Eric is hoping he will be able to sneak this code in as -fixes, which would allow the material to still land for Linux 4.5 if approved by DRM subsystem maintainer David Airlie and then in turn Linus Torvalds. The Broadcom developer's reasoning for trying to get it into -fixes right away is to help users, "My preference would be to get this in -fixes, since without GPU reset we can end up with a totally wedged desktop (and we do still have some known GPU hangs). If not, I'm fine with the first patch to -fixes and the other two to -next."
The GPU reset capability depends upon runtime power management for being able to turn off the GPU as part of the reset process. The VC4 driver previously had GPU reset support but it was disabled during a previous code refactoring process when dealing with a regression. With the runtime power management support, the VC4 DRM driver can turnoff the GPU in between rendering tasks, which is a feature not present in the closed-source Raspberry Pi graphics driver.
More details on the VC4 power management and GPU reset support can be found via this dri-devel patch series while waiting to see if it will still land in Linux 4.5.