renz496 :
Kepler and maxwell V1 did not fully compliance with DX11.1 specification but Maxwell V2 are including the new 12_1 feature level. In regards to DX11.2 both amd and nvidia have partial support for it but honestly i will not going to say that nvidia hardware (kepler and maxwell v1) are incapable of DX 11.2. In fact MS were using nvidia hardware when they first showcase the feature of DX11.2. And back then AMD make public statement about why they were late with DX11.2 drivers because MS direction with DX11.2.
As for DX11 i don't think there was anything that 'blocking' AMD drivers from performing as it should. If anything it is AMD that refused to support stuff like DCL for DX11
To put things into perspective... Look at this Wikipedia page almost at the bottom:
https://en.wikipedia.org/wiki/Feature_levels_in_Direct3D
You'll notice that;
GCN 1.0, 1.1 and 1.2 all support Resource binding tier 3, while Maxwell 2 supports Tier 2. Advantage for AMD.
GCN 1.1 and 1.2 support tiled resources tier 2, Maxwell 2 supports tier 3. Advantage for nVidia.
GCN does not support conservative rasterization, Maxwell 2 does. (this is 12_1 FL) Advantage for nVidia.
GCN does not support rasterizer-ordered views, Maxwell 2 does (the other 12_1 feature). Advantage for nVidia.
GCN 1.0, 1.1 and 1.2 all support Stencil reference value from Pixel Shader, no nVidia GPUs support this. Advantage for AMD.
GCN 1.0, 1.1 and 1.2 all support UAV slots for all stages tier 3, Kepler, Maxwell and Maxwell 2 support tier 2. Advantage for AMD.
The rest are pretty much the same. In other words, nVidia's 12_1 'advantage' is not really an advantage. They happen to support it while AMD doesn't. AMD supports things that nVidia doesn't. But 12_1 sounds nice because it seems like it's the newest thing.
If you really want to look at it in a very simplified, slightly incorrect but still indicative, nVidia has feature level 11_0 + 12_1, and AMD has 11_1 + 12_0. Neither of them has ALL the feature levels. Developers will decide which features they want to use. If they decide to use 12_1 features, nVidia will have the advantage. If they decide to use 11_1 features, AMD will have the advantage.