First let me clarify that I did not (yet) have the knowledge or even verified information, that this could be possible. But please bear with me and consider the information - maybe someone can spot the differences and help others improve the GPU performance.
So, in recent AMD materials for APU Carizzo was pictured a GPU Tonga, witch is present in Radeon R9 285 and feature 1792 stream processors, 32 ROP units and 256bit wide memory bus:
AMD GPU Tonga
However the catch is, that the die size of Tonga is 359 mm², witch is only slightly smaller that his predecesor, GPU Tahiti with it's 365 mm².
How does that matter? Well, there is very likely to be plenty of deactivated parts, giving the die size. Some people claimed, that AMD confirmed for them, that physicaly Tonga boast 2048 stream processors, not only 1792 active ones.
But there is something even more serious: from the picture is clear, that there is 2048 stream processors (32 CU) - and that there is, in fact, SIX 64bit memory bus controllers, witch means 6x64bit = 384bit wide memory bus is possible!
Now it is unclear, how many ROP units are actually on the chip: it could be 32 as in Tahiti, but it could be also 48 to simplify the memory interface - ROP units and memory controllers could be wired directly, as it is done with other chips.
So all in all it means, that GPU Tonga have the possibility of same power, as GPU Tahiti PLUS it have faster tesselation and delta compression. If there is 48 ROP units, then at same clocks as GPU Tahiti, this fully unlocked GPU Tonga could give about +20% of speed...!
If the number of ROP units remain at the Tahiti levels, it will give about 10% speed increase over Tahiti - eg. R9 290X card.
The fully active GPU Tonga will probably get marketed as R9 380X and the release data is unknown, but there is another thing that is possible: unlocking the chip DIY hacking.
Yes, we cannot change the memory bus interface (making memory bus wider is practically equivalent to creating a own card from scratch) on current R9 285 cards, but since these stream processors are deactivated likely by bios or some switch component(s) on the GPU itself, we can - theoretically - unlock the 2048 stream processors, witch could provide still a significant boost in the performance
It will be different to have a 1792 or 2048 stream processors - even the number of (at least active) ROP units remain at "low" 32...
Inspired by: http://www.pcgameshardware.de/AMD-Ra...2-CUs-1160632/