ACP is the Audo Co-Processor support found in new AMD APUs/SoCs. AMD developers had been working on the support for several months while the audio and power management related ACP code landed during the Linux 4.5 merge window. With that code now mainlined, AMD's Alex Deucher is looking to land the ACP driver support into the AMDGPU DRM driver.
It's new feature work that's landing late because of the sound/PM dependencies, but Alex is hoping it will still be accepted for Linux 4.5. He explained, "Chances of regressions are low since this just adds support for a new hw block. It does not modify any existing functionality. This enables audio on CZ asics which use i2s audio rather than azalia audio."
So the good news is that this AMDGPU ACP hook-up will yield working audio for AMD Carrizo systems utilizing i2s audio. Details via this pull request that was submitted today. He submitted the 600+ lines of new code to DRM subsystem maintainer David Airlie that will then need to get Linus Torvalds to accept this work still for Linux 4.5. Given that there will only be more Carrizo systems out there in time that utilize the ACP block, hopefully the feature is accepted for this kernel cycle.